PS Seminar Series - Paying the energy cost of C4 photosynthesis

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%.