Increasing agricultural productivity is one of the most important aims of modern biotechnology. One way to enhance the productivity of crop species is to enhance the efficiency of photosynthesis. In C3 plants the oxygenase activity of Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) limits the photosynthetic efficiency. The green microalgae Chlamydomonas reinhardtii has evolved a CO2 concentration mechanism (CCM) by increasing the CO2 concentration in the chloroplast stroma where RuBisCO is located. Four independent transgenic tobacco genotypes (LA, LB, C1 and C3) were generated producing the low CO2-inducible protein A and B (LCIA and LCIB) or the carbonic anhydrases I and III (CAH1 and CAH3) from C. reinhardtii CCM in the envelope, stroma, intermembrane space or thylakoid lumen of tobacco chloroplasts, respectively. All four recombinant proteins were active in planta, which had a substantial impact on carbon and nitrogen metabolism. Increasing the CO2 concentration near RuBisCO resulted in an enhanced rate of photosynthesis (by up to 15%), efficiency of photosystem II (by up to 18%) and chlorophyll content (by up to 19%). Although to differing extents, all four transgenic genotypes grew faster than wild-type plants, produced more shoot biomass (up to 45% more fresh weight or 38% more dry weight in the LA lines) and accumulated more photosynthetic end products, reflecting the higher rate of photosynthetic CO2 fixation. The proteome analysis revealed that the proteins changed in the transgenic genotypes compared to the wild-type plants were primarily associated with the regulation of the Calvin cycle and the amino acid biosynthesis. Metabolic analysis of the transgenic LA, LB and C3 plants revealed an increase in the levels of carbohydrates and also of most amino acids. Furthermore, transgenic LA and LB plants could maintain the enhanced biomass under low nitrogen conditions, where similarly-treated wild-type plants grew more slowly. The data generated in the present study confirmed that even single Chlamydomonas CCM components can be integrated into C3 plants to increase biomass, suggesting that transgenic lines combining multiple components or even a complete CCM could further increase the productivity and yield of C3 crops.

RWTH Aachen University, Diss., 2017; Aachen, 1 Online-Ressource (151 Seiten) : Illustrationen, Diagramme(2017). = RWTH Aachen University, Diss., 2017

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