Professor University of Massachusetts Amherst, Massachusetts
Body of Abstract: Glutathione (GSH) is a key antioxidant molecule that protects cells from oxidative stress and scavenges ROS. GSH homeostasis in plants is maintained via γ-glutamyl cycle i.e., synthesis, degradation, and recycling of its component amino acids. GSH biosynthesis pathways are well characterized in plants, however the steps for the degradation are not well known. Recently, we identified a small gene family encoding γ-glutamyl cyclotransferases, GGCTs, in Arabidopsis, which are involved in the γ-glutamyl cycle required for maintaining GSH homeostasis via recycling glutamate (Glu), a key nitrogen-storing amino acid. Manipulation of GGCT2;1 gene in Arabidopsis showed enhanced tolerance to toxic metals including arsenic, cadmium, mercury, and other abiotic stressors such as ABA and mannitol and produced higher levels of oxoproline (5-OP), a Glu precursor. Our studies suggest that by efficient recycling of Glu as part of the γ-glutamyl cycle, GGCT2;1 decreased the de novo synthesis of Glu, thereby increasing the nitrogen use efficiency. Further, AtGGCT2;1 overexpression lines accumulated significantly higher of 5-OP, acting as a bottleneck in glutamate recycling. For further conversion of 5-OP to Glu, we overexpressed oxoprolinase (OXP1) gene which further increased the plants tolerance to arsenic and mercury. To translate the research from the model plants Arabidopsis to field crops, we overexpressed a GCCT2;1 homologous gene from Camelina sativa (CsGGCT2;1) into Camelina. Transgenic Camelina lines also showed strong tolerance to toxic metals and caused more than 60% reduction of arsenic accumulation in roots and shoot tissues. Our results showed that these genes associated with GSH degradation in the γ-glutamyl cycle are ideal for developing climate resilient crops with enhanced tolerance to multiple abiotic stresses as well as reducing toxic metals accumulation for food safety via maintaining GSH homeostasis.