Regulatory mechanisms underlying C4 photosynthesis


Author for correspondence:
Thomas P. Brutnell
Tel: +01 607 254 8656



 Summary 9
II.Regulation of C4 differentiation11
III.The photorespiratory pathway: a case study for transcriptional and post-transcriptional controls14
IV.Future perspectives of C4 research – an introduction to a C4 model16


C4 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 C4 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 C4. 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 C4 regulation. Computational pipelines are being developed to accommodate the mass of data associated with these techniques. Finally, we discuss a readily transformable C4 grass –Setaria viridis– that has great potential to serve as a model for the genetic dissection of C4 photosynthesis in the grasses.