Strategies for engineering a two-celled C 4 photosynthetic pathway into rice

Abstract

Every day almost one billion people suffer from chronic hunger, and the situation is expected to deteriorate with a projected population growth to 9 billion worldwide by 2050. In order to provide adequate nutrition into the future, rice yields in Asia need to increase by 60%, a change that may be achieved by introduction of the C 4 photosynthetic cycle into rice. The international C 4 Rice Consortium was founded in order to test the feasibility of installing the C 4 engine into rice. This review provides an update on two of the many approaches employed by the C 4 Rice Consortium: namely, metabolic C 4 engineering and identification of determinants of leaf anatomy by mutant screens. The aim of the metabolic C 4 engineering approach is to generate a two-celled C 4 shuttle in rice by expressing the classical enzymes of the NADP-ME C 4 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 C 4-like fashion by specifically down-regulating their expression in rice mesophyll (M) cells. In addition to the changes in biochemistry, two-celled C 4 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. © 2011 The Author.