Sulfur Partitioning between Glutathione and Protein Synthesis Determines Plant Growth.

Photoautotrophic organisms must efficiently allocate their resources between stress-response pathways and growth-promoting pathways to be successful in a constantly changing environment. In this study, we addressed the coordination of sulfur flux between the biosynthesis of the reactive oxygen species scavenger glutathione (GSH) and protein translation as one example of a central resource allocation switch. We crossed the Arabidopsis () GSH synthesis-depleted cadmium-sensitive mutant, which lacks glutamate cysteine (Cys) ligase, into the sulfite reductase mutant, which suffers from a significantly decreased flux of sulfur into Cys and, consequently, is retarded in growth. Surprisingly, depletion of GSH synthesis promoted the growth of the double mutant () when compared with Determination of GSH levels and in vivo live-cell imaging of the reduction-oxidation-sensitive green fluorescent protein sensor demonstrated significant oxidation of the plastidic GSH redox potential in and This oxidized GSH redox potential aligned with significant activation of plastid-localized sulfate reduction and a significantly higher flux of sulfur into proteins. The specific activation of the serine/threonine sensor kinase Target of Rapamycin (TOR) in and was the trigger for reallocation of Cys from GSH biosynthesis into protein translation. Activation of TOR in enhanced ribosome abundance and partially rescued the decreased meristematic activity observed in mutants. Therefore, we found that the coordination of sulfur flux between GSH biosynthesis and protein translation determines growth via the regulation of TOR.