Novel roles of sulfur metabolism in stress-controlled stomata aperture regulation.

Stomatal closure allows plants to conserve water by reducing transpiration during drought. Surprisingly, the assimilation of the macronutrient sulfur is intimately connected to the drought stress response. This Tansley insight will only briefly touch on the general impact of sulfate assimilation on the production of drought-response metabolites. Instead, the emphasis will be on the unexpected role of cysteine in triggering guard cell-autonomous abscisic acid biosynthesis in response to diverse drought-associated stresses. A particular focus will be on identifying the chloroplast-localized cysteine synthase complex as a sensor hub that integrates long-distance soil-drying signals and local high-light signals to mediate stress-induced stomatal closure. Furthermore, we will discuss the emerging role of cysteine-derived sulfide as a signal in stomatal closure.