Review: Integration of sulfate assimilation with C and N metabolism in transition from C3 to C4 photosynthesis (J Exp Bot)

“Cysteine (HO₂CCH(NH₂)CH₂SH) synthesis is the converging point of the three major pathways of primary metabolism: carbon, nitrate, and sulfate assimilation.” It’s hard enough to coordinate two pathways, let alone three; but these metabolic connections are revealed in that a deficiency in one nutrient affects assimilation rates of the others. As yet, the connections between pathways are still being discovered, but in plants, the cysteine precursor O-acetylserine (OAS) and sulfide seem to be sensed. The coordination between C, N and S is rendered more complex in C4 plants, in which aspects of their assimilation is distributed between mesophyll and bundle sheath cells. In this review, Jobe et al. summarize the knowns and unknowns about how these three pathways are coordinated. They observe that efforts to engineer more-efficient C4 photosynthesis into C3 plants (like rice) will require a greater understanding of how C4 metabolism affects N and S assimilation.  (Summary by Mary Williams) J. Exp. Bot. 10.1093/jxb/erz250