Sulfur partitioning between glutathione and protein synthesis determines plant growth (Plant Physiol.)

Sulfur is incorporated into the amino acid cysteine (Cys) and also the reactive-oxygen scavenger glutathione (GSH). Speiser et al. investigated the effect of restricting both Cys and glutathione production through a double-mutant analysis in Arabidopsis; sir1-1 is a slow-growing sulfite-reductase deficient mutant with limited production of Cys production, and cad2-1 is cadmium sensitive due to a restriction in glutathione production. Interestingly, the sir1-1 cad2-1 double mutant is significantly larger than the sir1-1 single mutant. Further analysis indicated that there is an increased flux through the assimilatory sulfate reduction pathway in the double mutant. Furthermore, TOR (Target of Rapamycin) activity is induced in the cad2-1 mutant; TOR is a metabolic sensor kinase and a regulator of protein synthesis and growth in all eukaryotes. This study provides new evidence for the role of TOR in regulating plant growth. (Summary by Mary Williams) Plant Physiol. 10.1104/pp.18.00421