Variation in auxin sensing guides AUX/IAA transcriptional repressor ubiquitylation and destruction

Nat Commun. 2017 Jun 7;8:15706. doi: 10.1038/ncomms15706.

Abstract

Auxin is a small molecule morphogen that bridges SCFTIR1/AFB-AUX/IAA co-receptor interactions leading to ubiquitylation and proteasome-dependent degradation of AUX/IAA transcriptional repressors. Here, we systematically dissect auxin sensing by SCFTIR1-IAA6 and SCFTIR1-IAA19 co-receptor complexes, and assess IAA6/IAA19 ubiquitylation in vitro and IAA6/IAA19 degradation in vivo. We show that TIR1-IAA19 and TIR1-IAA6 have distinct auxin affinities that correlate with ubiquitylation and turnover dynamics of the AUX/IAA. We establish a system to track AUX/IAA ubiquitylation in IAA6 and IAA19 in vitro and show that it occurs in flexible hotspots in degron-flanking regions adorned with specific Lys residues. We propose that this signature is exploited during auxin-mediated SCFTIR1-AUX/IAA interactions. We present evidence for an evolving AUX/IAA repertoire, typified by the IAA6/IAA19 ohnologues, that discriminates the range of auxin concentrations found in plants. We postulate that the intrinsic flexibility of AUX/IAAs might bias their ubiquitylation and destruction kinetics enabling specific auxin responses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / metabolism
  • Arabidopsis Proteins / metabolism
  • Brassicaceae
  • F-Box Proteins / genetics
  • Gene Expression Profiling
  • Gene Expression Regulation, Plant*
  • Indoleacetic Acids / metabolism*
  • Kinetics
  • Nuclear Proteins / metabolism
  • Phylogeny
  • Plants, Genetically Modified / metabolism
  • Protein Binding
  • Protein Conformation
  • Receptors, Cell Surface / metabolism
  • Signal Transduction
  • Transcription, Genetic*
  • Ubiquitin / metabolism*
  • Ubiquitination*

Substances

  • Arabidopsis Proteins
  • F-Box Proteins
  • Indoleacetic Acids
  • Nuclear Proteins
  • Receptors, Cell Surface
  • Ubiquitin