Induction of Branched-Chain Amino Acid Aminotransferase Genes (GmBCATs) and ATG8 Homolog Genes in Response to Drought Stress in Soybean [Glycine max (L.) Merr.].

Severe drought stress causes crucial yield loss in soybean production and irreversible damage in soybean [Glycine max (L.) Merr.]. Recent studies in Arabidopsis, barley, and wheat have revealed that mitochondrial branched-chain amino acid aminotransferases (BCAT) in those plants are involved in the degradation of a branched-chain amino acid (BCAA) under water deficiency and/or shading treatment. It was examined whether autophagy and nutrient starvation signaling via cessation of photosynthesis are involved in the irreversible damage in soybean under drought stress. Leaf chlorophyll contents and photosystem II activity significantly decreased under drought stress condition. Drought stress on soybean up-regulated the expression levels of mitochondrial GmBCATs (mtGmBCAT), GmBCAT2 (Glyma.04g049200.1) and GmBCAT06g050100(Glyma.06g050100.1), and GmDREB2, a homologous gene of DREB (dehydration responsive element binding protein), but not GmBCAT01g(Glyma.01g196300.1), GmBCAT11g (Glyma.11g045300.1), GmBCAT08g063200, BCAT08g063300, GmBCAT07g. Furthermore, drought stress on soybean up-regulated the expression of GmATG8c, significantly, suggesting induction of autophagy in leaf. A line of evidence indicated that environmental stresses accelerate the degradation of chloroplast proteins by autophagy. Autophagy appeared to be regulated by the nutrient starvation signals of sugar and BCAA via SnRK1 and mTOR, respectively. Based on the present data, it is suggested that a combination of photosynthesis cessation and BCAA degradation in soybean under drought stress causes autophagy induction, leading to the irreversible damage of photosynthesis by autophagy-mediated protein degradation. [ABSTRACT FROM AUTHOR]