Coordination of auxin and ethylene biosynthesis by the aminotransferase VAS1

The VAS1 aminotransferase regulates the shade avoidance response in Arabidopsis thaliana by shunting metabolic flux away from auxin and ethylene, two growth regulatory plant hormones. We identify an Arabidopsis pyridoxal-phosphate–dependent aminotransferase, VAS1, whose loss-of-function simultaneously increases amounts of the phytohormone auxin and the ethylene precursor 1-aminocyclopropane-1-carboxylate. VAS1 uses the ethylene biosynthetic intermediate methionine as an amino donor and the auxin biosynthetic intermediate indole-3-pyruvic acid as an amino acceptor to produce L-tryptophan and 2-oxo-4-methylthiobutyric acid. Our data indicate that VAS1 serves key roles in coordinating the amounts of these two vital hormones.