Regulatory gateways for cell-specific gene expression in C4 leaves with Kranz anatomy

Abstract

C4 photosynthesis is a carbon-concentrating mechanism that increases delivery of carbon dioxide to RuBisCO and as a consequence reduces photorespiration. The C4 pathway is therefore beneficial in environments that promote high photorespiration. This pathway has evolved many times, and involves restricting gene expression to either mesophyll or bundle sheath cells. Here we review the regulatory mechanisms that control cell-preferential expression of genes in the C4 cycle. From this analysis, it is clear that the C4 pathway has a complex regulatory framework, with control operating at epigenetic, transcriptional, post-transcriptional, translational, and post-translational levels. Some genes of the C4 pathway are regulated at multiple levels, and we propose that this ensures robust expression in each cell type. Accumulating evidence suggests that multiple genes of the C4 pathway may share the same regulatory mechanism. The control systems for C4 photosynthesis gene expression appear to operate in C3 plants, and so it appears that pre-existing mechanisms form the basis of C4 photosynthesis gene expression.