Regulated amino acid accumulation under drought stress in Arabidopsis and tomato

Amino acids produced under drought-stress serve as osmolytes to protect plant cells against dehydration. Abscisic acid (ABA) regulates many osmotic stress responses, including production of many osmolytes. We have used mutants of tomato and Arabidopsis defective in ABA biosynthesis, to study drought-induced amino acid accumulation. In tomato mutants defective in ABA biosynthesis, we found that the accumulation of branched chain amino acids in drought-stressed leaves was significantly reduced compared to wild-type. However, these effects were rescued in ‘sit’ mutants by exogenous ABA supplementation, suggesting a direct role of ABA in amino acid biosynthesis. Analogous results were obtained in Arabidopsis ABA-defective mutants that also produced reduced amino acids under stress, in reproductive tissues. To understand the transcriptional regulation of drought-induced amino acid synthesis, we identified and used mutants of transcription factors that are strongly induced under drought-stress. Three transcription factor mutants accumulated significantly reduced amino acid content under stress, implying their function in regulating amino acid biosynthetic genes.