Abstract - Photosynthetic improvement has become a major focus for researchers seeking to increase yields of crop plants. The C4 Rice Project aims to introduce C₄ photosynthesis into C₃ plant rice with the goal of increasing rice production in developing countries. C₄ photosynthetic pathway is a biochemical carbon concentrating mechanism (CCM) that operates across two cell types to build up high CO₂ partial pressure in bundle sheath (BS) cells and allow Rubisco, confined in the BS, to operate at maximum capacity. However, running C₄ photosynthesis comes at higher energy cost as it requires at least two more ATP molecules per CO₂ fixed, compared to C₃ pathway. Studying C₄ thylakoid electron transport, that converts light energy into chemical energy of ATP, is therefore of primary importance for improving C₄ photosynthesis and introducing this pathway into C₃ plants. To get the extra ATP, BS cells of C₄ plants are proposed to run active cyclic electron flow (CEF). The NAD(P)H dehydrogenase (NDH) thylakoid protein complex, known to mediate one of the CEF routes in C₃ plants, is highly upregulated in the BS. To investigate the function of the complex, we knocked-out NDH in Setaria viridis, a model C₄ plant closely related to maize, sorghum and sugarcane. We show that NDH plays a central role in energetics of C₄ photosynthesis as its function goes far beyond the proposed role in CEF. These results are instrumental for understanding what modifications of electron transport in C₃ plants are required to cover the extra energy cost of C₄ photosynthesis or any other CCM.

Biography - Dr. Maria Ermakova’s research focuses on engineering photosynthesis to improve plant productivity. Dr. Ermakova is a Research Fellow in the C4 Rice Project and the ARC Centre of Excellence for Translational Photosynthesis at the Australian National University (ANU), working in the groups of Bob Furbank and Susanne von Caemmerer. Maria received her PhD from University of Turku (Finland) where she worked in Eva-Mari Aro’s group and discovered novel photoprotective pathways in cyanobacteria. At ANU, Maria studies biochemistry and energetics of C₄ plants, which have evolved a biochemical CO₂ concentrating mechanism allowing them to be more productive, but at higher energy cost. Genetic engineering to increase light-use efficiency of C₄ plants could further enhance their productivity and advance our understanding of C₄ photosynthesis. The latter is crucial for introducing C₄ pathway into C₃ plants, which is projected to boost productivity of crops by up to 50%.