Engineering Crops for Enhanced Tolerance to Multiple Abiotic Stresses and Improved N Use Efficiency Via Manipulating Novel-Stress Associated Proteins.

Environmental stresses adversely affect the growth and productivity of crop plants and thus are serious threats to agriculture. In order to increase crop productivity to meet the current global food demand, it is imperative to understand the underlying molecular and biochemical mechanisms for developing crops resistant to multiple abiotic stresses. Recently, members of Stress-Associated Proteins (SAP) gene family have been suggested to play significant roles in multiple abiotic stress responses in rice, however, their exact functions/molecular mechanisms are not known. In Arabidopsis and rice genomes, 14 and 18 genes, respectively, coding for SAP related proteins have been identified. These proteins contain either A20 or AN1 or both A20/AN1 zinc finger domains at the N- or C-terminal. Some SAP proteins also contain extra Cys2-His2 RING motifs at the C-terminus. We have manipulated the expression of several SAP genes in Arabidopsis and rice. Overexpression of AtSAP13 provided strong tolerance to multiple abiotic stresses such as salt, drought, and various toxic metals including zinc, cadmium, and arsenic, without causing a significant difference in metals accumulation. These plants attained significantly higher biomass and longer roots as compared to wild type plants under the stress condition. Whereas, the overexpression of AtSAP10 provided strong tolerance to heat, salt, zinc, nickel, and manganese. Further, as compared to wild type plants, AtSAP10 plants accumulated two-fold more Ni and Mn in roots and shoot tissues. In-silico analysis of the promoter sequences upstream of ATG start codon of AtSAPs using PLACE database predicted the presence of various abiotic stress related cis regulatory elements. We hypothesized that the expression of SAP genes might be regulated via the interaction of cis-elements present in the SAP promoters with abiotic stress related trans factors via protein-DNA interactions under different abiotic stresses. Through yeast one hybrid assay, we have proved this hypothesis and identified several transcription factors such as DREB, ERE, ZIP, HSE etc. that are interacting with the SAP promoters. Additionally, we have identified and overexpressed gamma-glutamyl cyclotransferase (GGCT), a gene from another stress related gene family, involved in GSH homeostasis. Overexpression of GGCT not only provided strong tolerance to oxidative stresses but also improved N use efficiency in plants under stress conditions. The knowledge and information gained here will not only be applied to engineering crops that will be better able to withstand such abiotic stresses and still produce sustainable yield but will also help to grow crops for food and biomass production on non-arable lands. Therefore, the proposed research could have a significant impact on global food security, biofuel production, and human and environment health enhancement.