Title: Towards C4 rice; Overexpression of C4 genes in Arabidopsis thaliana and Oryza sativa Enhances Photosynthesis, Plant Productivity and Water Use Efficiency

B C Tripathy

School of Life Sciences, JNU, India


Professor Baishnab C Tripathy studied Botany for his master’s degree.  Subsequently, he joined PhD program in Jawaharlal Nehru University, New Delhi and did his PhD on Primary Processes of Photosynthesis in 1981.  Subsequently, he did his post-doctoral research on chlorophyll biosynthesis and membrane bioenergetics in Ohio State University, Columbus, Ohio and University of Illinois, Urbana, USA from 1981-87.  After returning to India, he joined Jawaharlal Nehru University, New Delhi as Assistant Professor  in 1987 and promoted to full professor in 2001.  He has contributed a lot to Photosynthesis Research and has more than 100 research publications.


Plants with C4 photosynthesis are not only efficient in carbon assimilation, but they also have an advantage under unusual growth conditions. In C4 photosynthesis, the primary CO2 fixation is catalyzed by phosphoenolpyruvate carboxylase (PEPC). It is shown that overexpression of, both PEP Carboxylase and PEP Carboxykinase in Arabidopsis thaliana to have increased CO2 concentration in the vicinity of Rubisco. resulted in higher electron transport, carbon assimilation, increased biomass coupled with better water use efficiency.  Carbonic anhydrase (CA) catalyzes the inter-conversion of CO2 and bicarbonate used by the primary carboxylating enzymes of C3 and C4 plants respectively. Overexpression of cytosolic carbonic anhydrase (b-CA3) of the C4 dicot Flaveria bidentis in C3 Arabidopsis thaliana increased the photosynthetic efficiency of the transgenics. Due to a higher concentration of HCO3- in CA overexpressors, their PEPC activity increased generating more oxaloacetic acid and amino acids. Consequently, their total protein content increased resulting in higher Chl synthesis. The electron transport rate, CO2 assimilation rate, starch content, plant fresh weight and dry weight increased by 10-20% in CA overexpressors. Transgenic plants had lower stomatal conductance, reduced transpiration rate, and higher water use efficiency. Like C4 plants all the transgenics were tolerant to abiotic salt stress.  Transgenics had higher electron transport rate, better performance index and reduced generation of reduced generation of reactive oxygen species in the stress environment.  These approaches are being replicated in rice (Oryza sativa) to have increased photosynthesis, plant productivity, and grain yield.