Abstract
The formation and degradation of IAA-amino acid conjugates (IAA-aa) play an important role in auxin homeostasis. GH3s, early auxin-inducible genes, belong to the acyl-activating enzyme superfamily and encode IAA-aa synthetases. We designed and synthesized N-sulfamolyadenosine (SA) derivatives of auxins as intermediate analog inhibitors of IAA-aa synthetase on the basis of its catalytic mechanism. We previously showed that the SA derivatives are the potent inhibitors of GH3 in an in vitro enzyme assay. In this study, we examined their in vivo activities. In the excised Arabidopsis leaves treated with the exogenous IAA, the endogenous levels of IAA-aa (IAA-Asp, IAA-Glu, and IAA-Gln) greatly increased. When the SA derivatives were applied together with IAA, the increase was significantly repressed. Thus, the chemical approach inhibits all the GH3s involved in IAA-aa synthesis, and the inhibitors are expected to serve as a highly effective tool to study auxin homeostasis.
