DSpace Repository :: Browsing by Author "Bahaji, Abdellatif"

Browsing by Author "Bahaji, Abdellatif"

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Open Access
Arabidopsis responds to Alternaria alternata volatiles by triggering pPG-independent mechanisms
(American Society of Plant Biologists, 2016) Sánchez López, Ángela María; Bahaji, Abdellatif; Diego, Nuria de; Baslam, Marouane; Li, Jun; Muñoz Pérez, Francisco José; Almagro Zabalza, Goizeder; García Gómez, Pablo; Ameztoy del Amo, Kinia; Ricarte Bermejo, Adriana; Novák, Ondrej; Humplik, Jan F.; Spíchal, Lukás; Dolezal, Karel; Ciordia, Sergio; Mena, María Carmen; Navajas, Rosana; Baroja Fernández, Edurne; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Gobierno de Navarra / Nafarroako Gobernua (IIM010491.RI1); Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Volatile compounds (VCs) emitted by phylogenetically diverse microorganisms (including plant pathogens and microbes that do not normally interact mutualistically with plants) promote photosynthesis, growth, and the accumulation of high levels of starch in leaves through cytokinin (CK)-regulated processes. In Arabidopsis (Arabidopsis thaliana) plants not exposed to VCs, plastidic phosphoglucose isomerase (pPGI) acts as an important determinant of photosynthesis and growth, likely as a consequence of its involvement in the synthesis of plastidic CKs in roots. Moreover, this enzyme plays an important role in connecting the Calvin- Benson cycle with the starch biosynthetic pathway in leaves. To elucidate the mechanisms involved in the responses of plants to microbial VCs and to investigate the extent of pPGI involvement, we characterized pPGI-null pgi1-2 Arabidopsis plants cultured in the presence or absence of VCs emitted by Alternaria alternata. We found that volatile emissions from this fungal phytopathogen promote growth, photosynthesis, and the accumulation of plastidic CKs in pgi1-2 leaves. Notably, the mesophyll cells of pgi1-2 leaves accumulated exceptionally high levels of starch following VC exposure. Proteomic analyses revealed that VCs promote global changes in the expression of proteins involved in photosynthesis, starch metabolism, and growth that can account for the observed responses in pgi1-2 plants. The overall data show that Arabidopsis plants can respond to VCs emitted by phytopathogenic microorganisms by triggering pPGI-independent mechanisms.
Open Access
Cell-free microbial culture filtrates as candidate biostimulants to enhance plant growth and yield and activate soil- and plant-associated beneficial microbiota
(Frontiers Media, 2022) León Morcillo, Rafael Jorge; Baroja Fernández, Edurne; López-Serrano, Lidia; Leal-López, Jesús; Muñoz Pérez, Francisco José; Bahaji, Abdellatif; Férez-Gómez, Alberto; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
In this work we compiled information on current and emerging microbial-based fertilization practices, especially the use of cell-free microbial culture filtrates (CFs), to promote plant growth, yield and stress tolerance, and their effects on plant-associated beneficial microbiota. In addition, we identified limitations to bring microbial CFs to the market as biostimulants. In nature, plants act as metaorganisms, hosting microorganisms that communicate with the plants by exchanging semiochemicals through the phytosphere. Such symbiotic interactions are of high importance not only for plant yield and quality, but also for functioning of the soil microbiota. One environmentally sustainable practice to increasing crop productivity and/or protecting plants from (a)biotic stresses while reducing the excessive and inappropriate application of agrochemicals is based on the use of inoculants of beneficial microorganisms. However, this technology has a number of limitations, including inconsistencies in the field, specific growth requirements and host compatibility. Beneficial microorganisms release diffusible substances that promote plant growth and enhance yield and stress tolerance. Recently, evidence has been provided that this capacity also extends to phytopathogens. Consistently, soil application of microbial cell-free culture filtrates (CFs) has been found to promote growth and enhance the yield of horticultural crops. Recent studies have shown that the response of plants to soil application of microbial CFs is associated with strong proliferation of the resident beneficial soil microbiota. Therefore, the use of microbial CFs to enhance both crop yield and stress tolerance, and to activate beneficial soil microbiota could be a safe, efficient and environmentally friendly approach to minimize shortfalls related to the technology of microbial inoculation. In this review, we compile information on microbial CFs and the main constituents (especially volatile compounds) that promote plant growth, yield and stress tolerance, and their effects on plant-associated beneficial microbiota. In addition, we identify challenges and limitations for their use as biostimulants to bring them to the market and we propose remedial actions and give suggestions for future work.
Open Access
Células del mesófilo de plantas de arabidopsis que no poseen fosfoglucoisomerasa plastidial acumulan almidón
(2014) Ricarte Bermejo, Adriana; Muñoz Pérez, Francisco José; Bahaji, Abdellatif; Escuela Técnica Superior de Ingenieros Agrónomos; Nekazaritza Ingeniarien Goi Mailako Eskola Teknikoa
Está generalmente admitido que todo el proceso de biosíntesis del almidón que tiene lugar en las células del mesófilo de la hoja reside exclusivamente en el cloroplasto. Según esta interpretación el almidón transitorio es el producto final de una ruta metabólica en la que participan las enzimas fosfoglucomutasa plastidial (pPGM), ADPglucosa pirofosforilasa (AGP) y almidón sintasa (SS) que estaría conectada con el ciclo de Calvin-Benson a través de de la fosfoglucosa isomerasa plastidial (pPGI). Sin embargo, estudios llevados a cabo en el grupo “Metabolismo de Carbohidratos” del Instituto de Agrobiotecnología de Navarra han demostrado que hojas del mutante pgi1-2 sin actividad pPGI (a) acumulan en las células del mesófilo un 10% del almidón que poseen las hojas de una planta salvaje (WT), (b) poseen niveles WT de la molécula precursora del almidón, el ADP-glucosa, y (c) poseen una reducida capacidad fotosintética y una elevada actividad degradadora de almidón. En este trabajo nos planteamos producir y caracterizar un doble mutante pgi1-2/sex1 incapaz de degradar almidón. El rationale de esta aproximación experimental es que si el mutante pgi1-2 es capaz de acumular almidón en las células del mesófilo, las hojas del doble mutante pgi1-2/sex1 deberían acumular más almidón que las hojas pgi1-2, dado que el alelo sex1 impide que se degrade el almidón. Los resultados obtenidos en este trabajo (a) apoyan aún más la idea de que las células del mesófilo del mutante pgi1-2 acumulan almidón, y (b) soportan la existencia de importantes vía(s) alternativa(s) de síntesis de almidón diferentes a la vía clásica.
Open Access
Characterization of multiple SPS knockout mutants reveals redundant functions of the four Arabidopsis sucrose phosphate synthase isoforms in plant viability, and strongly indicates that enhanced respiration and accelerated starch turnover can alleviate the blockage of sucrose biosynthesis
(Elsevier, 2015) Bahaji, Abdellatif; Baroja Fernández, Edurne; Ricarte Bermejo, Adriana; Sánchez López, Ángela María; Muñoz Pérez, Francisco José; Baslam, Marouane; Almagro Zabalza, Goizeder; Sesma Pascual, María Teresa; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
We characterized multiple knock-out mutants of the four Arabidopsis sucrose phosphate synthase (SPSA1, SPSA2, SPSB and SPSC) isoforms. Despite their reduced SPS activity, spsa1/spsa2, spsa1/spsb, spsa2/spsb, spsa2/spsc, spsb/spsc, spsa1/spsa2/spsb and spsa2/spsb/spsc mutants displayed wild type (WT) vegetative and reproductive morphology, and showed WT photosynthetic capacity and respiration. In contrast, growth of rosettes, flowers and siliques of the spsa1/spsc and spsa1/spsa2/spsc mutants was reduced compared with WT plants. Furthermore, these plants displayed a high dark respiration phenotype. spsa1/spsb/spsc and spsa1/spsa2/spsb/spsc seeds poorly germinated and produced aberrant and sterile plants. Leaves of all viable sps mutants, except spsa1/spsc and spsa1/spsa2/spsc, accumulated WT levels of nonstructural carbohydrates. spsa1/spsc leaves possessed high levels of metabolic intermediates and activities of enzymes of the glycolytic and tricarboxylic acid cycle pathways, and accumulated high levels of metabolic intermediates of the nocturnal starch-to-sucrose conversion process, even under continuous light conditions. Results presented in this work show that SPS is essential for plant viability, reveal redundant functions of the four SPS isoforms in processes that are important for plant growth and nonstructural carbohydrate metabolism, and strongly indicate that accelerated starch turnover and enhanced respiration can alleviate the blockage of sucrose biosynthesis in spsa1/spsc leaves.
Open Access
Comparative genomic and phylogenetic analyses of gammaproteobacterial glg genes traced the origin of the Escherichia coli glycogen glgBXCAP operon to the last common ancestor of the sister orders enterobacteriales and pasteurellales
(Public Library of Science, 2015) Almagro Zabalza, Goizeder; Viale Bailone, Alejandro M.; Montero Macarro, Manuel; Rahimpour, Mehdi; Muñoz Pérez, Francisco José; Baroja Fernández, Edurne; Bahaji, Abdellatif; Zúñiga, Manuel; González Candelas, Fernando; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
Production of branched α-glucan, glycogen-like polymers is widely spread in the Bacteria domain. The glycogen pathway of synthesis and degradation has been fairly well characterized in the model enterobacterial species Escherichia coli (order Enterobacteriales, class Gammaproteobacteria), in which the cognate genes (branching enzyme glgB, debranching enzyme glgX, ADP-glucose pyrophosphorylase glgC, glycogen synthase glgA, and glycogen phosphorylase glgP) are clustered in a glgBXCAP operon arrangement. However, the evolutionary origin of this particular arrangement and of its constituent genes is unknown. Here, by using 265 complete gammaproteobacterial genomes we have carried out a comparative analysis of the presence, copy number and arrangement of glg genes in all lineages of the Gammaproteobacteria. These analyses revealed large variations in glg gene presence, copy number and arrangements among different gammaproteobacterial lineages. However, the glgBXCAP arrangement was remarkably conserved in all glg-possessing species of the orders Enterobacteriales and Pasteurellales (the E/P group). Subsequent phylogenetic analyses of glg genes present in the Gammaproteobacteria and in other main bacterial groups indicated that glg genes have undergone a complex evolutionary history in which horizontal gene transfer may have played an important role. These analyses also revealed that the E/P glgBXCAP genes (a) share a common evolutionary origin, (b) were vertically transmitted within the E/P group, and (c) are closely related to glg genes of some phylogenetically distant betaproteobacterial species. The overall data allowed tracing the origin of the E. coli glgBXCAP operon to the last common ancestor of the E/P group, and also to uncover a likely glgBXCAP transfer event from the E/P group to particular lineages of the Betaproteobacteria.
Open Access
Early development of the root-knot nematode Meloidogyne incognita
(BioMed Central, 2016) Calderón Urrea, Alejandro; Vanholme, Bartel; Vangestel, Sandra; Kane, Saben M.; Bahaji, Abdellatif; Pha, Khavong; García Solano, Miguel; Snider, Alyssa; Gheysen, Godelieve; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
Background: Detailed descriptions of the early development of parasitic nematodes are seldom available. The embryonic development of the plant-parasitic nematode Meloidogyne incognita was studied, focusing on the early events. Results: A fixed pattern of repeated cell cleavages was observed, resulting in the appearance of the six founder cells 3 days after the first cell division. Gastrulation, characterized by the translocation of cells from the ventral side to the center of the embryo, was seen 1 day later. Approximately 10 days after the first cell division a rapidly elongating two-fold stage was reached. The fully developed second stage juvenile hatched approximately 21 days after the first cell division. Conclusions: When compared to the development of the free-living nematode Caenorhabditis elegans, the development of M. incognita occurs approximately 35 times more slowly. Furthermore, M. incognita differs from C. elegans in the order of cell divisions, and the early cleavage patterns of the germ line cells. However, cytoplasmic ruffling and nuclear migration prior to the first cell division as well as the localization of microtubules are similar between C. elegans and M. incognita.
Open Access
Enhanced yield of pepper plants promoted by soil application of volatiles from cell-free fungal culture filtrates is associated with activation of the beneficial soil microbiota
(Frontiers Media, 2021) Baroja Fernández, Edurne; Almagro Zabalza, Goizeder; Sánchez López, Ángela María; Bahaji, Abdellatif; Gámez Arcas, Samuel; Diego, Nuria de; Dolezal, Karel; Muñoz Pérez, Francisco José; Climent Sanz, Eric; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Gobierno de Navarra / Nafarroako Gobernua
Plants communicate with microorganisms by exchanging chemical signals throughout the phytosphere. Such interactions are important not only for plant productivity and fitness, but also for terrestrial ecosystem functioning. It is known that beneficial microorganisms emit diffusible substances including volatile organic compounds (VOCs) that promote growth. Consistently, soil application of cell-free culture filtrates (CF) of beneficial soil and plant-associated microorganisms enhances plant growth and yield. However, how this treatment acts in plants and whether it alters the resident soil microbiota, are largely unknown. In this work we characterized the responses of pepper (Capsicum annuum L.) plants cultured under both greenhouse and open field conditions and of soil microbiota to soil application of CFs of beneficial and phytopathogenic fungi. To evaluate the contribution of VOCs occurring in the CFs to these responses, we characterized the responses of plants and of soil microbiota to application of distillates (DE) of the fungal CFs. CFs and their respective DEs contained the same potentially biogenic VOCs, and application of these extracts enhanced root growth and fruit yield, and altered the nutritional characteristics of fruits. High-throughput amplicon sequencing of bacterial 16S and fungal ITS rRNA genes of the soil microbiota revealed that the CF and DE treatments altered the microbial community compositions, and led to strong enrichment of the populations of the same beneficial bacterial and fungal taxa. Our findings show that CFs of both beneficial and phytopathogenic fungi can be used as biostimulants, and provide evidence that VOCs occurring in the fungal CFs act as mediators of the plants’ responses to soil application of fungal CFs through stimulation of the beneficial soil microbiota.
Open Access
Enhancing the expression of starch synthase class IV results in increased levels of both transitory and long-term storage starch
(Wiley, 2011) Gámez-Arjona, Francisco M.; Li, Jun; Raynaud, Sandy; Baroja Fernández, Edurne; Muñoz Pérez, Francisco José; Ovecka, Miroslav; Ragel, Paula; Bahaji, Abdellatif; Pozueta Romero, Javier; Mérida, Ángel; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
Starch is an important renewable raw material with an increasing number of applications. Several attempts have been made to obtain plants that produce modified versions of starch or higher starch yield. Most of the approaches designed to increase the levels of starch have focused on the increment of the amount of ADP‐glucose or ATP available for starch biosynthesis. In this work, we show that the overexpression of starch synthase class IV (SSIV) increases the levels of starch accumulated in the leaves of Arabidopsis by 30%–40%. In addition, SSIV‐overexpressing lines display a higher rate of growth. The increase in starch content as a consequence of enhanced SSIV expression is also observed in long‐term storage starch organs such as potato tubers. Overexpression of SSIV in potato leads to increased tuber starch content on a dry weight basis and to increased yield of starch production in terms of tons of starch/hectare. These results identify SSIV as one of the regulatory steps involved in the control of the amount of starch accumulated in plastids.
Open Access
Genetic and isotope ratio mass spectrometric evidence for the occurrence of starch degradation and cycling in illuminated Arabidopsis leaves
(Public Library of Science, 2017) Baslam, Marouane; Baroja Fernández, Edurne; Ricarte Bermejo, Adriana; Sánchez López, Ángela María; Aranjuelo Michelena, Iker; Bahaji, Abdellatif; Muñoz Pérez, Francisco José; Almagro Zabalza, Goizeder; Pujol, Pablo; Galarza, Regina; Teixidor, Pilar; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
Although there is a great wealth of data supporting the occurrence of simultaneous synthesis and breakdown of storage carbohydrate in many organisms, previous 13CO2 pulse-chase based studies indicated that starch degradation does not operate in illuminated Arabidopsis leaves. Here we show that leaves of gwd, sex4, bam4, bam1/bam3 and amy3/isa3/lda starch breakdown mutants accumulate higher levels of starch than wild type (WT) leaves when cultured under continuous light (CL) conditions. We also show that leaves of CL grown dpe1 plants impaired in the plastidic disproportionating enzyme accumulate higher levels of maltotriose than WT leaves, the overall data providing evidence for the occurrence of extensive starch degradation in illuminated leaves. Moreover, we show that leaves of CL grown mex1/ pglct plants impaired in the chloroplastic maltose and glucose transporters display a severe dwarf phenotype and accumulate high levels of maltose, strongly indicating that the MEX1 and pGlcT transporters are involved in the export of starch breakdown products to the cytosol to support growth during illumination. To investigate whether starch breakdown products can be recycled back to starch during illumination through a mechanism involving ADP-glucose pyrophosphorylase (AGP) we conducted kinetic analyses of the stable isotope carbon composition (δ13C) in starch of leaves of 13CO2 pulsed-chased WT and AGP lacking aps1 plants. Notably, the rate of increase of δ13C in starch of aps1 leaves during the pulse was exceedingly higher than that of WT leaves. Furthermore, δ13C decline in starch of aps1 leaves during the chase was much faster than that of WT leaves, which provides strong evidence for the occurrence of AGP-mediated cycling of starch breakdown products in illuminated Arabidopsis leaves.
Open Access
Glucose-6-P/phosphate translocator2 mediates the phosphoglucose-isomerase1-independent response to microbial volatiles
(Oxford University Press, 2022) Gámez Arcas, Samuel; Muñoz, Francisco José; Ricarte Bermejo, Adriana; Sánchez López, Ángela María; Baslam, Marouane; Baroja Fernández, Edurne; Bahaji, Abdellatif; Almagro Zabalza, Goizeder; Diego, Nuria de; Dolezal, Karel; Novák, Ondrej; Leal-López, Jesús; León Morcillo, Rafael Jorge; Castillo, Araceli G.; Pozueta Romero, Javier; Agronomía, Biotecnología y Alimentación; Agronomia, Bioteknologia eta Elikadura
In Arabidopsis (Arabidopsis thaliana), the plastidial isoform of phosphoglucose isomerase (PGI1) mediates photosynthesis, metabolism, and development, probably due to its involvement in the synthesis of isoprenoid-derived signals in vascular tissues. Microbial volatile compounds (VCs) with molecular masses of 545 Da promote photosynthesis, growth, and starch overaccumulation in leaves through PGI1-independent mechanisms. Exposure to these compounds in leaves enhances the levels of GLUCOSE-6-PHOSPHATE/PHOSPHATE TRANSLOCATOR2 (GPT2) transcripts. We hypothesized that the PGI1-independent response to microbial volatile emissions involves GPT2 action. To test this hypothesis, we characterized the responses of wild-type (WT), GPT2-null gpt2-1, PGI1-null pgi1-2, and pgi1-2gpt2-1 plants to small fungal VCs. In addition, we characterized the responses of pgi1-2gpt2-1 plants expressing GPT2 under the control of a vascular tissue- and root tip-specific promoter to small fungal VCs. Fungal VCs promoted increases in growth, starch content, and photosynthesis in WT and gpt2-1 plants. These changes were substantially weaker in VC-exposed pgi1-2gpt2-1 plants but reverted to WT levels with vascular and root tip-specific GPT2 expression. Proteomic analyses did not detect enhanced levels of GPT2 protein in VC-exposed leaves and showed that knocking out GPT2 reduced the expression of photosynthesis-related proteins in pgi1-2 plants. Histochemical analyses of GUS activity in plants expressing GPT2-GUS under the control of the GPT2 promoter showed that GPT2 is mainly expressed in root tips and vascular tissues around hydathodes. Overall, the data indicated that the PGI1-independent response to microbial VCs involves resetting of the photosynthesis-related proteome in leaves through long-distance GPT2 action.
Open Access
HPLC-MS/MS analyses show that the near-starchless aps1 and pgm leaves accumulate wild type levels of ADPglucose: further evidence for the occurrence of important ADPglucose biosynthetic pathway(s) alternative to the pPGI-pPGM-AGP pathway
(Public Library of Science, 2014) Bahaji, Abdellatif; Baroja Fernández, Edurne; Sánchez López, Ángela María; Muñoz Pérez, Francisco José; Li, Jun; Almagro Zabalza, Goizeder; Montero Macarro, Manuel; Pujol, Pablo; Galarza, Regina; Kaneko, Kentaro; Oikawa, Kazusato; Wada, Kaede; Mitsui, Toshiaki; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Gobierno de Navarra / Nafarroako Gobernua, IIM010491.RI1
In leaves, it is widely assumed that starch is the end-product of a metabolic pathway exclusively taking place in the chloroplast that (a) involves plastidic phosphoglucomutase (pPGM), ADPglucose (ADPG) pyrophosphorylase (AGP) and starch synthase (SS), and (b) is linked to the Calvin-Benson cycle by means of the plastidic phosphoglucose isomerase (pPGI). This view also implies that AGP is the sole enzyme producing the starch precursor molecule, ADPG. However, mounting evidence has been compiled pointing to the occurrence of important sources, other than the pPGI-pPGM-AGP pathway, of ADPG. To further explore this possibility, in this work two independent laboratories have carried out HPLC-MS/ MS analyses of ADPG content in leaves of the near-starchless pgm and aps1 mutants impaired in pPGM and AGP, respectively, and in leaves of double aps1/pgm mutants grown under two different culture conditions. We also measured the ADPG content in wild type (WT) and aps1 leaves expressing in the plastid two different ADPG cleaving enzymes, and in aps1 leaves expressing in the plastid GlgC, a bacterial AGP. Furthermore, we measured the ADPG content in ss3/ss4/aps1 mutants impaired in starch granule initiation and chloroplastic ADPG synthesis. We found that, irrespective of their starch contents, pgm and aps1 leaves, WT and aps1 leaves expressing in the plastid ADPG cleaving enzymes, and aps1 leaves expressing in the plastid GlgC accumulate WT ADPG content. In clear contrast, ss3/ss4/aps1 leaves accumulated ca. 300 foldmore ADPG than WT leaves. The overall data showed that, in Arabidopsis leaves, (a) there are important ADPG biosynthetic pathways, other than the pPGI-pPGM-AGP pathway, (b) pPGM and AGP are not major determinants of intracellular ADPG content, and (c) the contribution of the chloroplastic ADPG pool to the total ADPG pool is low.
Open Access
Plastidial phosphoglucose isomerase is an important determinant of seed yield through its involvement in gibberellin-mediated reproductive development and storage reserve biosynthesis in arabidopsis
(American Society of Plant Biologists, 2018) Bahaji, Abdellatif; Almagro Zabalza, Goizeder; Ezquer, Ignacio; Gámez Arcas, Samuel; Sánchez López, Ángela María; Muñoz Pérez, Francisco José; Barrio, Ramón José; Sampedro, M. Carmen; Diego, Nuria de; Spíchal, Lukás; Dolezal, Karel; Tarkowská, Danuse; Caporali, Elisabetta; Mendes, Marta Adelina; Baroja Fernández, Edurne; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Gobierno de Navarra / Nafarroako Gobernua, ref. P1004 PROMEBIO
The plastid-localized phosphoglucose isomerase isoform PGI1 is an important determinant of growth in Arabidopsis thaliana, likely due to its involvement in the biosynthesis of plastidial isoprenoid-derived hormones. Here, we investigated whether PGI1 also influences seed yields. PGI1 is strongly expressed in maturing seed embryos and vascular tissues. PGI1-null pgi1-2 plants had ∼60% lower seed yields than wild-type plants, with reduced numbers of inflorescences and thus fewer siliques and seeds per plant. These traits were associated with low bioactive gibberellin (GA) contents. Accordingly, wild-type phe-notypes were restored by exogenous GA application. pgi1-2 seeds were lighter and accumulated ∼50% less fatty acids (FAs) and ∼35% less protein than wild-type seeds. Seeds of cytokinin-deficient plants overexpressing CYTOKININ OXIDASE/DE-HYDROGENASE1 (35S:AtCKX1) and GA-deficient ga20ox1 ga20ox2 mutants did not accumulate low levels of FAs, and exogenous application of the cytokinin 6-benzylaminopurine and GAs did not rescue the reduced weight and FA content of pgi1-2 seeds. Seeds from reciprocal crosses between pgi1-2 and wild-type plants accumulated wild-type levels of FAs and proteins. Therefore, PGI1 is an important determinant of Arabidopsis seed yield due to its involvement in two processes: GA-mediated reproductive development and the metabolic conversion of plastidial glucose-6-phosphate to storage reserves in the embryo.
Open Access
Plastidic phosphoglucose isomerase is an important determinant of starch accumulation in mesophyll cells, growth, photosynthetic capacity, and biosynthesis of plastidic cytokinins in Arabidopsis
(Public Library of Science, 2015) Bahaji, Abdellatif; Sánchez López, Ángela María; Diego, Nuria de; Muñoz Pérez, Francisco José; Baroja Fernández, Edurne; Li, Jun; Ricarte Bermejo, Adriana; Baslam, Marouane; Aranjuelo Michelena, Iker; Almagro Zabalza, Goizeder; Humplik, Jan F.; Novák, Ondrej; Spíchal, Lukás; Dolezal, Karel; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Gobierno de Navarra / Nafarroako Gobernua, IIM010491.RI2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Phosphoglucose isomerase (PGI) catalyzes the reversible isomerization of glucose-6-phosphate and fructose-6-phosphate. It is involved in glycolysis and in the regeneration of glucose-6-P molecules in the oxidative pentose phosphate pathway (OPPP). In chloroplasts of illuminated mesophyll cells PGI also connects the Calvin-Benson cycle with the starch biosynthetic pathway. In this work we isolated pgi1-3, a mutant totally lacking pPGI activity as a consequence of aberrant intron splicing of the pPGI encoding gene, PGI1. Starch content in pgi1-3 source leaves was ca. 10-15% of that of wild type (WT) leaves, which was similar to that of leaves of pgi1-2, a T-DNA insertion pPGI null mutant. Starch deficiency of pgi1 leaves could be reverted by the introduction of a sex1 null mutation impeding β-amylolytic starch breakdown. Although previous studies showed that starch granules of pgi1-2 leaves are restricted to both bundle sheath cells adjacent to the mesophyll and stomata guard cells, microscopy analyses carried out in this work revealed the presence of starch granules in the chloroplasts of pgi1-2 and pgi1-3 mesophyll cells. RT-PCR analyses showed high expression levels of plastidic and extra-plastidic β-amylase encoding genes in pgi1 leaves, which was accompanied by increased β-amylase activity. Both pgi1-2 and pgi1-3 mutants displayed slow growth and reduced photosynthetic capacity phenotypes even under continuous light conditions. Metabolic analyses revealed that the adenylate energy charge and the NAD(P)H/NAD(P) ratios in pgi1 leaves were lower than those of WT leaves. These analyses also revealed that the content of plastidic 2-C-methyl-D-erythritol 4-phosphate (MEP)-pathway derived cytokinins (CKs) in pgi1 leaves were exceedingly lower than in WT leaves. Noteworthy, exogenous application of CKs largely reverted the low starch content phenotype of pgi1 leaves. The overall data show that pPGI is an important determinant of photosynthesis, energy status, growth and starch accumulation in mesophyll cells likely as a consequence of its involvement in the production of OPPP/glycolysis intermediates necessary for the synthesis of plastidic MEP-pathway derived hormones such as CKs.
Open Access
Regulation of the response of plants to volatile compounds emitted by fungal phytopathogens
(2020) García Gómez, Pablo; Pozueta Romero, Javier; Bahaji, Abdellatif; Farrán Blanch, Inmaculada; Agronomía, Biotecnología y Alimentación; Agronomia, Bioteknologia eta Elikadura
El crecimiento y el desarrollo de las plantas están afectados por microorganismos presentes en la filosfera, la rizosfera y/o la endosfera. En la fase de precolonización, antes de que se establezca un contacto físico con la planta, bacterias y hongos beneficiosos sintetizan una gran cantidad de sustancias que fomentan el crecimiento de la planta. Tales sustancias fomentan además la formación de raíces laterales y el crecimiento de pelos radiculares, mejorando así la capacidad exploratoria de las raíces para obtener agua y minerales del suelo y aumentando la superficie de la raíz y, por tanto, su predisposición para ser colonizada e infectada. Estos microorganismos también emiten un gran número de compuestos volátiles (VCs), con masa molecular inferior a 300 Da y alta presión de vapor, que promueven el crecimiento de la planta y la fotosíntesis y modulan la arquitectura de la raíz. Recientemente, el grupo de investigación en el que he realizado mis investigaciones demostró que esta capacidad no está restringida a microorganismos beneficiosos, sino que también se extiende a patógenos. Esta tesis doctoral se ha llevado a cabo con la doble intención de identificar la naturaleza de los VCs microbianos con propiedades bioestimulantes y profundizar en el conocimiento de los mecanismos implicados en la respuesta de las raíces a los VCs emitidos por microorganismos patógenos.
Open Access
Reply to Smith et al.: No evidence to challenge the current paradigm on starch and cellulose biosynthesis involving sucrose synthase activity
(National Academy of Sciences, 2012) Baroja Fernández, Edurne; Muñoz Pérez, Francisco José; Bahaji, Abdellatif; Almagro Zabalza, Goizeder; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
In our opinion, no pressing biological evidence has been presented by Barratt et al. to challenge the current paradigm on cellulose and starch metabolism involving SUS activity. In this context, we must emphasize that Angeles-Núñez and Tiessen have shown that SUS2 and SUS3 are required for channeling carbon toward ADP-glucose and starch in Arabidopsis seeds.
Open Access
The role of plastidic phosphoglucose isomerase in the response of Arabidopsis thaliana to volatile compounds emitted by pathogenic microorganisms
(2016) Sánchez López, Ángela María; Pozueta Romero, Javier; Bahaji, Abdellatif; Producción Agraria; Nekazaritza Ekoizpena
El almidón es un homopolímero ramificado de residuos de glucosa unidos covalentemente a través de enlaces de tipo α-1,4 y α-1,6. Sintetizado en el plastidio, este polisacárido de reserva constituye la forma principal de almacenamiento de carbohidratos en plantas superiores y un determinante importante tanto del crecimiento de la planta como de su relación con el entorno. Está ampliamente aceptado que el proceso de biosíntesis del almidón en hojas tiene lugar exclusivamente en el cloroplasto. Según esta interpretación, el almidón es el producto fi nal de una ruta metabólica conectada con el ciclo de Calvin- Benson (CBC) a través de la fosfoglucosa isomerasa plastidial (pPGI). Esta enzima cataliza la conversión de moléculas de fructosa-6-fosfato del CBC en moléculas de glucosa-6-fosfato, las cuales son metabolizadas en almidón a través de la acción combinada de la fosfoglucomutasa, la ADP-glucosa pirofosforilasa y la almidón sintasa. Las plantas perciben estímulos bióticos mediante el reconocimiento de una gran cantidad de compuestos procedentes de los organismos con los que interactúan. En este sentido cabe destacar que los microorganismos de la rizosfera sintetizan una gran cantidad de sustancias que regulan el desarrollo y el crecimiento de la planta. Además, estos microorganismos emiten una amplia gama de compuestos volátiles (VCs) que actúan como “infoquímicos” en la comunicación entre la planta y el microorganismo. Estudios llevados a cabo por el grupo de investigación en el que he desarrollado este trabajo de tesis doctoral demostraron que los VCs emitidos por una amplia gama de microorganismos (incluyendo patógenos y especies que normalmente no interactúan con la planta) fomentan la acumulación de cantidades excepcionalmente elevadas almidón en la planta. Dada la falta de conocimiento sobre los mecanismos implicados en este fenómeno y teniendo en cuenta a su vez el papel importante que juega el almidón en la interacción de la planta con su entorno, en este trabajo de tesis doctoral investigué las bases moleculares implicadas en la respuesta de la planta a los VCs microbianos, prestando especial atención al papel que juega la pPGI en esta respuesta. El primer capítulo de este trabajo describe la caracterización de dos mutantes (pgi1-2 y pgi1-3) carentes de actividad pPGI. Ambos acumulan en sus hojas un 10- 15% del almidón existente en hojas de plantas salvaje (WT). Contrariamente a lo que pudiera esperarse al tener en cuenta la interpretación clásica de la biosíntesis de almidón, análisis por microscopía revelaron la presencia de gránulos de almidón en cloroplastos de las células del mesófi lo de estos mutantes. Tanto pgi1-2 como pgi1-3 mostraron un crecimiento lento, una reducida capacidad fotosintética y un bajo balance NAD(P)H/NAD(P) con respecto a plantas WT. Estudios hormonómicos mostraron que el contenido de citoquininas (CKs) plastidiales en hojas pgi1 es muy reducido con respecto al existente en hojas WT. Además la aplicación exógena de CKs revirtió el fenotipo de defi ciencia de almidón de hojas de plantas pgi1. Los datos presentados en este trabajo indican que pPGI es un importante determinante de la fotosíntesis, el estado redox de la célula, el crecimiento y la acumulación de almidón en células del mesófi lo como consecuencia de su implicación en la producción de intermediarios de la vía oxidativa de las pentosas fosfato/glicólisis necesarios para la síntesis CKs plastidiales y poder reductor. El capítulo 2 muestra que VCs emitidos por microorganismos fi logenéticamente distantes (incluyendo bacterias y hongos benefi ciosos y patógenos) promueven el crecimiento, la acumulación de niveles excepcionalmente elevados de almidón y la fl oración en varias especies de plantas, incluidos cultivos de interés agronómico. Además, plantas de Arabidopsis expuestas a VCs emitidos por el fi topatógeno Alternaria alternata experimentaron un incremento en la fotosíntesis y un aumento del contenido de CKs. La magnitud de este fenómeno fue reducida en el mutante 35S:AtCKX1 defi ciente en CKs y en el mutante ahk2/3 de señalización de CKs, proporcionando así evidencia de que este tipo de hormonas juega un papel importante en la respuesta de las plantas a VCs microbianos. El análisis transcriptómico de hojas de Arabidopsis expuestas a VCs de A. alternata reveló cambios en la expresión de genes regulados por luz y CKs implicados en la fotosíntesis, la fl oración, el crecimiento y el metabolismo del almidón. Sorprendentemente, una gran cantidad de genes diferencialmente expresados en plantas tratadas con VCs de A. alternata son genes cuya expresión se ve alterada también en plantas expuestas a VCs emitidos por la bacteria benefi ciosa Bacillus subtilis GB03, sugiriendo que las plantas han desarrollado la capacidad de reaccionar a VCs emitidos por diferentes microorganismos a través de la activación o estimulación de mecanismos altamente conservados. Para entender mejor los mecanismos implicados en las respuestas de las plantas a los VCs emitidos por microorganismos e investigar en qué medida pPGI está implicada en este fenómeno, en el trabajo presentado en el capítulo 3 se caracterizó la respuesta del mutante pgi1-2 a los VCs emitidos por A. alternata. VCs emitidos por este hongo fi topatógeno promovieron el crecimiento, la fotosíntesis y la acumulación de CKs plastidiales en hojas pgi1-2. Contra todo pronóstico, VCs emitidos por A. alternata promovieron la acumulación de niveles excepcionalmente elevados de almidón en hojas pgi1-2. Análisis proteómicos revelaron que los VCs microbianos promueven cambios en la acumulación de proteínas involucradas en la fotosíntesis, el metabolismo del almidón y el crecimiento que pueden explicar las respuestas observadas en plantas pgi1-2. Los datos presentados en este capítulo muestran que las plantas de Arabidopsis son capaces de responder a VCs microbianos mediante la activación o la estimulación de mecanismos independientes de pPGI.
Open Access
Sucrose synthase activity in the sus1/sus2/sus3/sus4 Arabidopsis mutant is sufficient to support normal cellulose and starch production
(National Academy of Sciences, 2011) Baroja Fernández, Edurne; Muñoz Pérez, Francisco José; Li, Jun; Bahaji, Abdellatif; Almagro Zabalza, Goizeder; Montero Macarro, Manuel; Etxeberria, Ed; Hidalgo Cruz, Maite; Sesma Pascual, María Teresa; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Sucrose synthase (SUS) catalyzes the reversible conversion of sucrose and a nucleoside diphosphate into the corresponding nucleoside diphosphate-glucose and fructose. In Arabidopsis, a multigene family encodes six SUS (SUS1-6) isoforms. The involvement of SUS in the synthesis of UDP-glucose and ADP-glucose linked to Arabidopsis cellulose and starch biosynthesis, respectively, has been questioned by Barratt et al. [(2009) Proc Natl Acad Sci USA 106:13124–13129], who showed that (i) SUS activity in wild type (WT) leaves is too low to account for normal rate of starch accumulation in Arabidopsis, and (ii) different organs of the sus1/sus2/sus3/sus4 SUS mutant impaired in SUS activity accumulate WT levels of ADP-glucose, UDP-glucose, cellulose and starch. However, these authors assayed SUS activity under unfavorable pH conditions for the reaction. By using favorable pH conditions for assaying SUS activity, in this work we show that SUS activity in the cleavage direction is sufficient to support normal rate of starch accumulation in WT leaves. We also demonstrate that sus1/sus2/sus3/sus4 leaves display WT SUS5 and SUS6 expression levels, whereas leaves of the sus5/sus6 mutant display WT SUS1–4 expression levels. Furthermore, we show that SUS activity in leaves and stems of the sus1/sus2/sus3/sus4 and sus5/sus6 plants is ~85% of that of WT leaves, which can support normal cellulose and starch biosynthesis. The overall data disprove Barratt et al. (2009) claims, and are consistent with the possible involvement of SUS in cellulose and starch biosynthesis in Arabidopsis.
Open Access
Systematic production of inactivating and non-inactivating suppressor mutations at the relA locus that compensate the detrimental effects of complete spoT loss and affect glycogen content in Escherichia coli
(Public Library of Science, 2014) Montero Macarro, Manuel; Rahimpour, Mehdi; Viale Bailone, Alejandro M.; Almagro Zabalza, Goizeder; Eydallin, Gustavo; Sevilla, Ángel; Cánovas, Manuel; Bernal, Cristina; Lozano, Ana Belén; Muñoz Pérez, Francisco José; Baroja Fernández, Edurne; Bahaji, Abdellatif; Mori, Hirotada; Codoñer, Francisco M.; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In Escherichia coli, ppGpp is a major determinant of growth and glycogen accumulation. Levels of this signaling nucleotide are controlled by the balanced activities of the ppGpp RelA synthetase and the dual-function hydrolase/synthetase SpoT. Here we report the construction of spoT null (DspoT) mutants obtained by transducing a DspoT allele from DrelADspoT double mutants into relA+ cells. Iodine staining of randomly selected transductants cultured on a rich complex medium revealed differences in glycogen content among them. Sequence and biochemical analyses of 8 DspoT clones displaying glycogen-deficient phenotypes revealed different inactivating mutations in relA and no detectable ppGpp when cells were cultured on a rich complex medium. Remarkably, although the co-existence of DspoT with relA proficient alleles has generally been considered synthetically lethal, we found that 11 DspoT clones displaying high glycogen phenotypes possessed relA mutant alleles with non-inactivating mutations that encoded stable RelA proteins and ppGpp contents reaching 45–85% of those of wild type cells. None of the DspoT clones, however, could grow on M9-glucose minimal medium. Both Sanger sequencing of specific genes and high-throughput genome sequencing of the DspoT clones revealed that suppressor mutations were restricted to the relA locus. The overall results (a) defined in around 4 nmoles ppGpp/g dry weight the threshold cellular levels that suffice to trigger net glycogen accumulation, (b) showed that mutations in relA, but not necessarily inactivating mutations, can be selected to compensate total SpoT function(s) loss, and (c) provided useful tools for studies of the in vivo regulation of E. coli RelA ppGpp synthetase.
Open Access
Transformación genética de cebada con At-SSIV y análisis de su efecto en el metabolismo del almidón y biomasa
(2011) Moleres Apilluelo, Javier; Bahaji, Abdellatif; Baroja Fernández, Edurne; Escuela Técnica Superior de Ingenieros Agrónomos; Nekazaritza Ingeniarien Goi Mailako Eskola Teknikoa
El almidón es el principal carbohidrato de reserva en plantas. Este metabolito es empleado por la planta para su crecimiento y desarrollo durante la ausencia de luz. Este valioso polisacárido es acumulado en órganos heterotróficos, tales como semillas de cereales, raíces de cassava y tubérculos de patata. El almidón representa la fuente más importante de carbohidratos en la dieta humana y posee muchas aplicaciones tanto comerciales como industriales (Delcour et al., 2010). Se han llevado a cabo muchas investigaciones a través de la ingeniería genética con el fin de mejorar el rendimiento y calidad de almidón, respondiendo a la demanda del sector industrial. Estudios recientes han demostrado que la almidón sintasa clase IV (starch synthase class IV, SSIV) de Arabidopsis Thaliana está envuelta en la iniciación de gránulos de almidón en hojas ya que el doble mutante en los genes SSIII y SSIV mostró un menor contenido de almidón las mismas (Szydlowski et al., 2009). Más significativo resulta el hecho de que la sobreexpresión de At-SSIV en Arabidopsis induce la acumulación de almidón en hojas y aumenta el contenido de almidón en tubérculos de patata (Gámez-Arjona et al., 2011). Con el objeto de caracterizar el papel de SSIV en la producción de biomasa y almidón tanto en órganos autótrofos como en heterótrofos, se generarán líneas de cebada (Golden Promise c.v.) que sobre-expresan SSIV y SSIV fusionada a la proteína verde fluorescente (SSIV-GFP). La transformación genética de la cebada fue llevada a cabo siguiendo el método descrito por Hansel et al. (2004) mediante la cepa de Agrobacterium Tumefaciens AGL1, utilizando los vectores binarios, PBract214-AtSSIV y PBract214-AtSSIV-GFP. Primeramente se seleccionarán líneas transgénicas de cebada mediante germinación en medio selectivo y análisis por PCR. Seguidamente se realizarán análisis por western blot para comprobar la expresión de SSIV y SSIV-GFP. Por último, se cuantificará el contenido en almidón y la biomasa en semillas y hojas de las líneas transgénicas de cebada seleccionadas.
Open Access
Volatile compounds emitted by diverse phytopathogenic microorganisms promote plant growth and flowering through cytokinin action
(John Wiley & Sons, 2016) Sánchez López, Ángela María; Baslam, Marouane; Muñoz Pérez, Francisco José; Bahaji, Abdellatif; Almagro Zabalza, Goizeder; Ricarte Bermejo, Adriana; García Gómez, Pablo; Baroja Fernández, Edurne; Pozueta Romero, Javier; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Gobierno de Navarra / Nafarroako Gobernua (IIM010491.RI1); Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
It is known that volatile emissions from some beneﬁcial rhizosphere microorganisms promote plant growth. Here we show that volatile compounds (VCs) emitted by phylogenetically diverse rhizosphere and non-rhizhosphere bacteria and fungi (including plant pathogens and microbes that do not normally interact mutualistically with plants) promote growth and ﬂowering of various plant species, including crops. In Arabidopsis plants exposed to VCs emitted by the phytopathogen Alternaria alternata, changes included enhancement of photosynthesis and accumulation of high levels of cytokinins (CKs) and sugars. Evidence obtained using transgenic Arabidopsis plants with altered CK status show that CKs play essential roles in this phenomenon, because growth and ﬂowering responses to the VCs were reduced in mutants with CK-deﬁciency (35S:AtCKX1) or low receptor sensitivity (ahk2/3). Further, we demonstrate that the plant responses to fungal VCs are light-dependent. Transcriptomic analyses of Arabidopsis leaves exposed to A. alternata VCs revealed changes in the expression of light- and CK-responsive genes involved in photosynthesis, growth and ﬂowering. Notably, many genes differentially expressed in plants treated with fungal VCs were also differentially expressed in plants exposed to VCs emitted by the plant growth promoting rhizobacterium Bacillus subtilis GB03, suggesting that plants react to microbial VCs through highly conserved regulatory mechanisms.