Regulatory mechanisms underlying C-4 photosynthesis

C-4 photosynthesis is an adaptation that evolved to alleviate the detrimental effects of photorespiration as a result of the gradual decline in atmospheric carbon dioxide levels. In most C-4 plants, two cell types, bundle sheath and mesophyll, cooperate in carbon fixation, and, in so doing, are able to alleviate photorespiratory losses. Although much of the biochemistry is well characterized, little is known about the genetic mechanisms underlying the cell-type specificity driving C-4. However, several studies have shown that regulation acts at multiple levels, including transcriptional, post-transcriptional, post-translational and epigenetic. One example of such a regulatory mechanism is the cell-specific accumulation of major photorespiratory transcripts/proteins in bundle sheath cells, where ribulose-1,5-bisphosphate carboxylase/oxygenase is localized. Although many of the genes are expressed in the bundle sheath, some are expressed in both cell types, implicating post-transcriptional control mechanisms. Recently, ultra-high-throughput sequencing techniques and sophisticated mass spectrometry instrumentation have provided new opportunities to further our understanding of C-4 regulation. Computational pipelines are being developed to accommodate the mass of data associated with these techniques. Finally, we discuss a readily transformable C-4 grass -Setaria viridis- that has great potential to serve as a model for the genetic dissection of C-4 photosynthesis in the grasses.