Broadening the roles of UDP-glycosyltransferases in auxin homeostasis and plant development

The levels of the important plant growth regulator indole-3-acetic acid (IAA) are tightly controlled within plant tissues to spatiotemporally orchestrate concentration gradients that drive plant growth and development. Metabolic inactivation of bioactive IAA is known to participate in the modulation of IAA maxima and minima. IAA can be irreversibly inactivated by oxidation and conjugation to aspartate and glutamate. Usually overlooked because of its reversible nature, the most abundant inactive IAA form is the IAA-glucose (IAA-glc) conjugate. Glycosylation of IAA in Arabidopsis thaliana is reported to be carried out by UDP-glycosyltransferase 84B1 (UGT84B1), while UGT74D1 has been implicated in the glycosylation of the irreversibly formed IAA catabolite oxIAA. Here we demonstrated that both UGT84B1 and UGT74D1 modulate IAA levels throughout plant development by dual IAA and oxIAA glycosylation. Moreover, we identified a novel UGT subfamily whose members redundantly mediate the glycosylation of oxIAA and modulate skotomorphogenic growth.

Automated summary

The levels of the important plant growth regulator IAA are tightly controlled within plant tissues through metabolic inactivation, modulation of concentration gradients, and glycosylation processes; UGT84B1 and UGT74D1 have been identified as key enzymes in the glycosylation of IAA and oxIAA, which play crucial roles in regulating plant growth and development. Additionally, a novel UGT subfamily has been discovered to redundantly mediate the glycosylation of oxIAA and modulate skotomorphogenic growth.