Apoplastic gamma-glutamyl transferase activity encoded by GGT1 and GGT2 is important for vegetative and generative development

Gamma-glutamyl transferase (GGT; EC 2.3.2.2) is the only enzyme capable of degrading glutathione (GSH) in extra-cytosolic spaces. In plant cells, the GGT1 and GGT2 isoforms are located in the apoplast, bound respectively to the cell wall and the plasma membrane. GGT1 is expressed throughout plants, mainly in the leaves and vascular system, while GGT2 is more specifically expressed in seeds and trichomes, and weakly in roots. Their role in plant physiology remains to be clarified, however. Obtaining the ggt1/ggt2 double mutant can offer more clues than the corresponding single mutants, and to prevent any compensatory expression between the two isoforms. In this work, ggt1/ggt2 RNAi (RNA interference) lines were generated and characterized in the tissues where both isoforms are expressed. The seed yield was lower in the ggt1/ggt2 RNAi plants due to the siliques being fewer in number and shorter in length, with no changes in thiols and sulfur compounds. Proline accumulation and delayed seed germination were seen in one line. There were also fewer trichomes (which contain high levels of GSH) in the RNAi lines than in the wild type, and the root elongation rate was slower. In conclusion, apoplastic GGT silencing induces a decrease in the number of organs with a high GSH demand (seeds and trichomes) as a result of resource reallocation to preserve integrity and composition

Systems analysis of metabolism and the transcriptome in Arabidopsis thaliana roots reveals differential co-regulation upon iron, sulfur and potassium deficiency

Deprivation of mineral nutrients causes significant retardation of plant growth. This retardation is associated with nutrient specific and general stress-induced transcriptional responses. In this study we adjusted the external supply of iron, potassium and sulfur to cause the same retardation of shoot growth. Nevertheless, limitation by individual nutrients resulted in specific morphological adaptations and distinct shifts within the root metabolite fingerprint. The metabolic shifts affected key metabolites of primary metabolism and the stress-related phytohormones, jasmonic-, salicylic- and abscisic acid. These phytohormone signatures contributed to specific nutrient deficiency-induced transcriptional regulation. Limitation by the micronutrient iron caused the strongest regulation and affected 18 % of the root transcriptome. Only 130 genes were regulated by all nutrients. Specific co-regulation between the iron and sulfur metabolic routes upon iron or sulfur deficiency was observed. Interestingly, iron deficiency caused regulation of a different set of genes of the sulfur assimilation pathway compared to sulfur deficiency itself, which demonstrates the presence of specific signal-transduction systems for the cross-regulation of the pathways. Combined iron and sulfur starvation experiments demonstrated that a requirement for a specific nutrient can overrule this cross-regulation. The comparative metabolomics and transcriptomics approach used dissected general-stress from nutrient-specific regulation in roots of Arabidopsis

Sulfur availability regulates plant growth via glucose-TOR signaling

Plants lack the amino acid sensors that regulate TOR in metazoans. Here Dong et al. show that Arabidopsis GCN2 senses carbon and nitrogen availability for cysteine synthesis while sulfur limitation activates TOR via glucose metabolism, providing a mechanism whereby plants control growth according to nutrient availability