Open Access
Physiological performance of transplastomic tobacco plants overexpressing aquaporin AQP1 in chloroplast membranes
(Oxford University Press, 2018) Fernández San Millán, Alicia; Aranjuelo Michelena, Iker; Ancín Rípodas, María; Larraya Reta, Luis María; Farrán Blanch, Inmaculada; Veramendi Charola, Jon; Agronomia, Bioteknologia eta Elikadura; Agronomía, Biotecnología y Alimentación; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
The leaf mesophyll CO2 conductance and the concentration of CO2 within the chloroplast are major factors affecting photosynthetic performance. Previous studies have shown that the aquaporin NtAQP1 (which localizes to the plasma membrane and chloroplast inner envelope membrane) is involved in CO2 permeability in the chloroplast. Levels of NtAQP1 in plants genetically engineered to overexpress the protein correlated positively with leaf mesophyll CO2 conductance and photosynthetic rate. In these studies, the nuclear transformation method used led to changes in NtAQP1 levels in the plasma membrane and the chloroplast inner envelope membrane. In the present work, NtAQP1 levels were increased up to 16-fold in the chloroplast membranes alone by the overexpression of NtAQP1 from the plastid genome. Despite the high NtAQP1 levels achieved, transplastomic plants showed lower photosynthetic rates than wild-type plants. This result was associated with lower Rubisco maximum carboxylation rate and ribulose 1,5-bisphosphate regeneration. Transplastomic plants showed reduced mesophyll CO2 conductance but no changes in chloroplast CO2 concentration. The absence of differences in chloroplast CO2 concentration was associated with the lower CO2 fixation activity of the transplastomic plants. These findings suggest that non-functional pores of recombinant NtAQP1 may be produced in the chloroplast inner envelope membrane.
Open Access
Overexpression of thioredoxin m in tobacco chloroplasts inhibits the protein kinase STN7 and alters photosynthetic performance
(Oxford University Press, 2019) Ancín Rípodas, María; Fernández San Millán, Alicia; Larraya Reta, Luis María; Morales Iribas, Fermín; Veramendi Charola, Jon; Aranjuelo Michelena, Iker; Farrán Blanch, Inmaculada; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
The activity of the protein kinase STN7, involved in phosphorylation of the light-harvesting complex II (LHCII) proteins, has been reported as being co-operatively regulated by the redox state of the plastoquinone pool and the ferredoxin–thioredoxin (Trx) system. The present study aims to investigate the role of plastid Trxs in STN7 regulation and their impact on photosynthesis. For this purpose, tobacco plants overexpressing Trx f or m from the plastid genome were characterized, demonstrating that only Trx m overexpression was associated with a complete loss of LHCII phosphorylation that did not correlate with decreased STN7 levels. The absence of phosphorylation in Trx m-overexpressing plants impeded migration of LHCII from PSII to PSI, with the concomitant loss of PSI–LHCII complex formation. Consequently, the thylakoid ultrastructure was altered, showing reduced grana stacking. Moreover, the electron transport rate was negatively affected, showing an impact on energy-demanding processes such as the Rubisco maximum carboxylation capacity and ribulose 1,5-bisphosphate regeneration rate values, which caused a strong depletion in net photosynthetic rates. Finally, tobacco plants overexpressing a Trx m mutant lacking the reactive redox site showed equivalent physiological performance to the wild type, indicating that the overexpressed Trx m deactivates STN7 in a redox-dependent way.
Open Access
Elevated CO2 has concurrent effects on leaf and grain metabolism but minimal effects on yield in wheat
(Oxford University Press, 2020) Tcherkez, Guillaume; Ben Mariem, Sinda; Larraya Reta, Luis María; García Mina, José M.; Zamarreño, Ángel M.; Paradela, Alberto; Cui, Jing; Badeck, Franz-Werner; Meza, Diego; Rizza, Fulvia; Bunce, James; Han, Xue; Tausz-Posch, Sabine; Cattivelli, Luigi; Fangmeier, Andreas; Aranjuelo Michelena, Iker; Agronomía, Biotecnología y Alimentación; Agronomia, Bioteknologia eta Elikadura; Gobierno de Navarra / Nafarroako Gobernua, PI040 TRIGOCLIM
While the general effect of CO2 enrichment on photosynthesis, stomatal conductance, N content, and yield has been documented, there is still some uncertainty as to whether there are interactive effects between CO2 enrichment and other factors, such as temperature, geographical location, water availability, and cultivar. In addition, the metabolic coordination between leaves and grains, which is crucial for crop responsiveness to elevated CO2, has never been examined closely. Here, we address these two aspects by multi-level analyses of data from several free-air CO2 enrichment experiments conducted in five different countries. There was little effect of elevated CO2 on yield (except in the USA), likely due to photosynthetic capacity acclimation, as reflected by protein profiles. In addition, there was a significant decrease in leaf amino acids (threonine) and macroelements (e.g. K) at elevated CO2, while other elements, such as Mg or S, increased. Despite the non-significant effect of CO2 enrichment on yield, grains appeared to be significantly depleted in N (as expected), but also in threonine, the S-containing amino acid methionine, and Mg. Overall, our results suggest a strong detrimental effect of CO2 enrichment on nutrient availability and remobilization from leaves to grains.
Open Access
Overexpression of thioredoxin m in chloroplasts alters carbon and nitrogen partitioning in tobacco
(Oxford University Press, 2021) Ancín Rípodas, María; Larraya Reta, Luis María; Florez-Sarasa, Igor; Bénard, Camille; Fernández San Millán, Alicia; Veramendi Charola, Jon; Gibon, Yves; Fernie, Alisdair R.; Aranjuelo Michelena, Iker; Farrán Blanch, Inmaculada; Agronomia, Bioteknologia eta Elikadura; Institute for Multidisciplinary Research in Applied Biology - IMAB; Agronomía, Biotecnología y Alimentación
In plants, there is a complex interaction between carbon (C) and nitrogen (N) metabolism, and its coordination is fundamental for plant growth and development. Here, we studied the influence of thioredoxin (Trx) m on C and N partitioning using tobacco plants overexpressing Trx m from the chloroplast genome. The transgenic plants showed altered metabolism of C (lower leaf starch and soluble sugar accumulation) and N (with higher amounts of amino acids and soluble protein), which pointed to an activation of N metabolism at the expense of carbohydrates. To further delineate the effect of Trx m overexpression, metabolomic and enzymatic analyses were performed on these plants. These results showed an up-regulation of the glutamine synthetase-glutamate synthase pathway; specifically tobacco plants overexpressing Trx m displayed increased activity and stability of glutamine synthetase. Moreover, higher photorespiration and nitrate accumulation were observed in these plants relative to untransformed control plants, indicating that overexpression of Trx m favors the photorespiratory N cycle rather than primary nitrate assimilation. Taken together, our results reveal the importance of Trx m as a molecular mediator of N metabolism in plant chloroplasts.
Open Access
Assessing the evolution of wheat grain traits during the last 166 years using archived samples
(Nature Research, 2020) Mariem, S.B.; Gámez Guzmán, Angie Lorena; Larraya Reta, Luis María; Fuertes Mendizabal, Teresa; Cañameras, Nuria; Araus, José Luis; Aranjuelo Michelena, Iker; McGrath, Steve P.; Hawkesford, Malcolm J.; González Murua, Carmen; Gaudeul, Myriam; Medina, Leopoldo; Paton, Alan; Cattivelli, Luigi; Fangmeier, Andreas; Bunce, James; Tausz-Posch, Sabine; Macdonald, Andy J.; Agronomia, Bioteknologia eta Elikadura; Institute for Multidisciplinary Research in Applied Biology - IMAB; Agronomía, Biotecnología y Alimentación
The current study focuses on yield and nutritional quality changes of wheat grain over the last 166 years. It is based on wheat grain quality analyses carried out on samples collected between 1850 and 2016. Samples were obtained from the Broadbalk Continuous Wheat Experiment (UK) and from herbaria from 16 different countries around the world. Our study showed that, together with an increase in carbohydrate content, an impoverishment of mineral composition and protein content occurred. The imbalance in carbohydrate/protein content was specially marked after the 1960’s, coinciding with strong increases in ambient [CO2] and temperature and the introduction of progressively shorter straw varieties. The implications of altered crop physiology are discussed.