AtMYB93 is a novel negative regulator of lateral root development in Arabidopsis.

Daniel J Gibbs,Susan A Harding,Anushree Choudhary,Kamal Swarup,Candida Nibau,George W Bassel,Jessica Fannon,Susan J Bradshaw,Dov J Stekel,Erika Yamada,Ute Voß,Malcolm J Bennett,Laura A Moody,Juliet C Coates,Julien Lavenus

doi:10.1111/nph.12879

Abstract

Plant root system plasticity is critical for survival in changing environmental conditions. One important aspect of root architecture is lateral root development, a complex process regulated by hormone, environmental and protein signalling pathways.Here we show, using molecular genetic approaches, that the MYB transcription factor AtMYB93 is a novel negative regulator of lateral root development in Arabidopsis.We identify AtMYB93 as an interaction partner of the lateral-root-promoting ARABIDILLO proteins. Atmyb93 mutants have faster lateral root developmental progression and enhanced lateral root densities, while AtMYB93-overexpressing lines display the opposite phenotype. AtMYB93 is expressed strongly, specifically and transiently in the endodermal cells overlying early lateral root primordia and is additionally induced by auxin in the basal meristem of the primary root. Furthermore, Atmyb93 mutant lateral root development is insensitive to auxin, indicating that AtMYB93 is required for normal auxin responses during lateral root development.We propose that AtMYB93 is part of a novel auxin-induced negative feedback loop stimulated in a select few endodermal cells early during lateral root development, ensuring that lateral roots only develop when absolutely required. Putative AtMYB93 homologues are detected throughout flowering plants and represent promising targets for manipulating root systems in diverse crop species.

Highlights

Plant rooting systems are fundamental for absorbing nutrients and water, anchoring the plant to its substrate, and responding to internal and external signals
One important aspect of root architecture is lateral root development, a complex process regulated by hormone, environmental and protein signalling pathways
Atmyb93 mutant lateral root development is insensitive to auxin, indicating that AtMYB93 is required for normal auxin responses during lateral root development

Summary

Introduction

Plant rooting systems are fundamental for absorbing nutrients and water, anchoring the plant to its substrate, and responding to internal and external signals. The root systems of most vascular plants are formed by branching of lateral roots (LRs) from a primary root (PR) that first develops during embryogenesis. This process has been studied in great detail in several flowering plants, Arabidopsis (Osmont et al, 2007; Nibau et al, 2008; De Smet, 2012). The endodermis, the cell layer immediately overlying the pericycle, has recently been identified as a key regulator of LR developmental progression (Duan et al, 2013; Marhavy et al, 2013; Vermeer et al, 2014). The endodermis undergoes local remodelling and morphological changes during the very early stages of LR development, to accommodate the developing LRP (Vermeer et al, 2014), and regulates later LR emergence events (Duan et al, 2013)

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