The Regulation of Gene Expression Required for C4 Photosynthesis

C4 photosynthesis is normally associated with the compartmentation of photosynthesis between mesophyll (M) and bundle sheath (BS) cells. The mechanisms regulating the differential accumulation of photosynthesis proteins in these specialized cells are fundamental to our understanding of how C4 photosynthesis operates. Cell-specific accumulation of proteins in M or BS can be mediated by posttranscriptional processes and translational efficiency as well as by differences in transcription. Individual genes are likely regulated at multiple levels. Although cis-elements have been associated with cell-specific expression in C4 leaves, there has been little progress in identifying trans-factors. When C4 photosynthesis genes from C4 species are placed in closely related C3 species, they are often expressed in a manner faithful to the C4 cycle. Next-generation sequencing and comprehensive analysis of the extent to which genes from C4 species are expressed in M or BS cells of C3 plants should provide insight into how the C4 pathway is regulated and evolved.