Overexpression of plastidial thioredoxin f leads to enhanced starch accumulation in tobacco leaves

[EN] Starch, the most abundant storage carbohydrate in plants, has been a major feedstock for first generation biofuels. Growing fuel demands require, however, that the starch yields of energy crops be improved. Leaf starch is synthesised during the day and degraded at night to power nonphotosynthetic metabolism. Redox regulation has been associated with the coordination of the enzymes involved in starch metabolism, but neither the signals nor mechanisms that regulate this metabolism are entirely clear. In this work, the thioredoxin (Trx) f and m genes, which code for key enzymes in plastid redox regulation, were overexpressed from the plastid genome. Tobacco plants overexpressing Trx f, but not Trx m, showed an increase of up to 700% in leaf starch accumulation, accompanied by an increase in leaf sugars, specific leaf weight (SLW), and leaf biomass yield. To test the potential of these plants as a nonfood energy crop, tobacco leaves overexpressing Trx f were subjected to enzymatic hydrolysis, and around a 500% increase in the release of fermentable sugars was recorded. The results show that Trx f is a more effective regulator of photosynthetic carbon metabolism in planta than Trx m. The overexpression of Trx f might therefore provide a means of increasing the carbohydrate content of plants destined for use in biofuel production. It might also provide a means of improving the nutritional properties of staple food crops.The authors are grateful to M. Saenz, M. Duran, O. Asiain and especially Ma.J. Villafranca for their excellent plant care and cultivation and to J. Carballeda, L. Villanueva, and O. Martinez for their technical assistance. We thank the staff at the Electron Microscopy Service of UPV (Valencia) for their excellent technical help. We gratefully acknowledge CENER for its help with the enzymatic hydrolysis assays. This work was supported by grants from Gobierno de Navarra (IIM10865.RI1) and Ministerio de Ciencia e Innovacion (AGL2010-15107). R.S.-B. and P.M.-C. were supported by predoctoral fellowships from CSIC and G. Valenciana (Spain), respectively.Sanz-Barrio, R.; Corral Martínez, P.; Ancin, M.; Seguí-Simarro, JM.; Farran, I. (2013). Overexpression of plastidial thioredoxin f leads to enhanced starch accumulation in tobacco leaves. Plant Biotechnology Journal. 11(5):618-627. https://doi.org/10.1111/pbi.12052S61862711