Cell-type-specific differentiation of chloroplasts in C4 plants.

In leaves of C4 grasses such as maize, photosynthetic activities are partitioned between bundle-sheath and mesophyll cells, leading to increased photosynthetic yield, particularly under stress conditions. As we discuss here, recent comparative chloroplast proteome analyses in maize have shown specific adaptation to C4-cell-specific differentiation of the photosynthetic apparatus, primary and secondary metabolism and metabolite transporters, as well as the chloroplast protein homeostasis machinery. Furthermore, a novel bundle-sheath-enriched 1000-kDa NADPH dehydrogenase 'supercomplex' has been identified, and we discuss its possible role in inorganic carbon concentration. These breakthroughs provide new opportunities to further unravel C4 pathways and to increase crop productivity through metabolic engineering of C4 pathways into C3 plants, such as rice.