Chemical inhibition of the auxin inactivation pathway uncovers the roles of metabolic turnover in auxin homeostasis

The phytohormone auxin, indole-3-acetic acid (IAA), plays a prominent role in plant development. Auxin homeostasis is coordinately regulated by auxin synthesis, transport, and inactivation; however, the physiological contribution of auxin inactivation to auxin homeostasis has not been determined. The GH3 IAA-amino acid conjugating enzymes play a central role in auxin inactivation. Chemical inhibition of GH3 proteins in planta is challenging because the inhibition of these enzymes leads to IAA overaccumulation that rapidly induces GH3 expression. Here, we report the characterization of a potent GH3 inhibitor, kakeimide, that selectively targets IAA-conjugating GH3 proteins. Chemical knockdown of the auxin inactivation pathway demonstrates that auxin turnover is very rapid (about 10 min) and indicates that both auxin biosynthesis and inactivation dynamically regulate auxin homeostasis.

Automated summary

The phytohormone auxin, indole-3-acetic acid (IAA), plays a significant role in plant development. The research characterizes a potent GH3 inhibitor called kakeimide that selectively targets IAA-conjugating GH3 proteins. Chemical knockdown experiments demonstrate that auxin turnover is rapid, suggesting that both auxin biosynthesis and inactivation dynamically regulate auxin homeostasis.