Person: Li, Jun
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Li
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Jun
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Instituto de Agrobiotecnología (IdAB)
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Publication 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 InstitutuaStarch 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.Publication 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 PublikoaPhosphoglucose 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.Publication 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 PublikoaVolatile 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.