Progress on C4 Rice Project -- Vein Spacing and Beyond

The demand for food of the growing population continues to increase over the years. Rice being the staple food of most Asian countries has not reached its full potential being a C3 crop. C4 plants on the other hand have a higher photosynthetic capacity and are more efficient in utilizing water and nutrients. Our research is a part of a large multinational consortium tasked with introducing C4 characteristics into rice.  This seminar provides an overview of the many approaches employed by the C4 Rice Consortium: namely, metabolic C4 engineering and identification of determinants of leaf anatomy by mutant screens. The aim of the metabolic C4 engineering approach is to generate a two-celled C4 shuttle in rice by expressing the classical enzymes of the NADP-ME C4 cycle in a cell-appropriate manner. The aim is also to restrict RuBisCO and glycine decarboxylase expression to the bundle sheath (BS) cells of rice in a C4-like fashion by specifically down-regulating their expression in rice mesophyll (M) cells. In addition to the changes in biochemistry, two-celled C4 species show a convergence in leaf anatomy that include increased vein density and reduced numbers of M cells between veins. By screening rice activation-tagged lines and loss-of-function sorghum mutants we endeavour to identify genes controlling these key traits. In this presentation, we outline the strategy being adopted by the C4 rice consortium to engineer a more efficient photosynthetic pathway into rice. We also summarize related research in this area.