The 5'-3' Exoribonuclease XRN4 Regulates Auxin Response via the Degradation of Auxin Receptor Transcripts.

David Windels,Etienne Bucher

doi:10.3390/genes9120638

David Windels, Etienne Bucher

Open Access

https://doi.org/10.3390/genes9120638

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Abstract

Auxin is a major hormone which plays crucial roles in instructing virtually all developmental programs of plants. Its signaling depends primarily on its perception by four partially redundant receptors of the TIR1/AFB2 clade (TAARs), which subsequently mediate the specific degradation of AUX/IAA transcriptional repressors to modulate the expression of primary auxin-responsive genes. Auxin homeostasis depends on complex regulations at the level of synthesis, conjugation, and transport. However, the mechanisms and principles involved in the homeostasis of its signaling are just starting to emerge. We report that xrn4 mutants exhibit pleiotropic developmental defects and strong auxin hypersensitivity phenotypes. We provide compelling evidences that these phenotypes are directly caused by improper regulation of TAAR transcript degradation. We show that the cytoplasmic 5′-3′ exoribonuclease XRN4 is required for auxin response. Thus, our work identifies new targets of XRN4 and a new level of regulation for TAAR transcripts important for auxin response and for plant development.

Highlights

Plant growth, organogenesis, and diverse responses to environmental changes are control by auxins plant hormones [1,2]
We show that xrn4 mutants are unable to properly regulate the turn-over of TRANSPORT INHIBITOR RESPONSE 1 (TIR1)/AUXIN SIGNALLING F-BOX PROTEIN2 (AFB2) auxin receptor (TAAR) transcripts and that chemical suppression of TAAR functions leads to suppression of certain developmental defects observed in xrn4 plants
We have shown here that the 50 -30 exoribonuclease XRN4 is a component of the auxin signaling pathway and that this function is achieved through a mechanism involving controlled degradation of TAAR transcripts

Summary

Introduction

Organogenesis, and diverse responses to environmental changes are control by auxins plant hormones [1,2]. There are four TAARs genes which have partially-redundant functions [3,4,5]. TAAR proteins belong to SKIP/CULLIN/F-BOX (SCF)-ubiquitin ligase complexes and in presence of auxins can form a complex with AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) transcriptional repressors [6,7,8]. These AUX/IAA proteins are ubiquitinated and degraded by the 26S proteasome [6]. The degradation of AUX/IAA induces the release of AUXIN RESPONSE FACTOR (ARF) transcription factors. ARFs leads to the activation (5 ARFs) or to the repression (18 ARFs) of primary auxin-responsive genes [1,9,10]

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