Autophagy functions in bulk degradation of proteins and organelles for nutrient recycling. Recent evidence suggests that a set of autophagy-related (ATG) genes are induced under starvation, senescence and various abiotic stresses. To understand how these genes function in plants, expression profiles of soybean ATG homologs, GmATG8s, GmATG4, GmATG9, GmATG12 and GmATG18a, were examined using seedlings of Glycine max (L.) Merr. cv. Fukuyutaka) subjected to various nutrient conditions. Among them, GmATG8i mRNA was induced at higher level than any other ATGs under starvation. Immuoblot with a specific antibody raised against GmAtg8i indicated that endogenous GmAtg8i associates to microsomes of soybean seedling extracts. In the presence of vacuolar protease inhibitors, significant accumulation of anti-GmAtg8i was observed and mRNA level of GmATG8i increased in higher level than in the absence of the inhibitors. These results suggest that in soybean gene expression of ATG8i is regulated by both environmental nutrient conditions and intracellular nutrient recycling via proteolysis in vacuole.
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