Short-Root regulates primary, lateral, and adventitious root development in Arabidopsis.

Mikaël Lucas,Alan Marchant,Malcolm J Bennett,Jiehua Wang,Kamal Swarup,Morag Whitworth,Benjamin Peret,Tony Pridmore,Klaus Palme,Susan Zappala,Karin Ljung,Ranjan Swarup,Ilda Casimiro,Goran Sandberg,Stefan Mairhofer,David Lake,Michael J Holdsworth,Ivan A Paponov,Sacha Mooney

doi:10.1104/pp.110.165126

Abstract

Short-Root (SHR) is a well-characterized regulator of radial patterning and indeterminacy of the Arabidopsis (Arabidopsis thaliana) primary root. However, its role during the elaboration of root system architecture remains unclear. We report that the indeterminate wild-type Arabidopsis root system was transformed into a determinate root system in the shr mutant when growing in soil or agar. The root growth behavior of the shr mutant results from its primary root apical meristem failing to initiate cell division following germination. The inability of shr to reactivate mitotic activity in the root apical meristem is associated with the progressive reduction in the abundance of auxin efflux carriers, PIN-FORMED1 (PIN1), PIN2, PIN3, PIN4, and PIN7. The loss of primary root growth in shr is compensated by the activation of anchor root primordia, whose tissues are radially patterned like the wild type. However, SHR function is not restricted to the primary root but is also required for the initiation and patterning of lateral root primordia. In addition, SHR is necessary to maintain the indeterminate growth of lateral and anchor roots. We conclude that SHR regulates a wide array of Arabidopsis root-related developmental processes.

Highlights

SHORT-ROOT (SHR) is a well-characterized regulator of radial patterning and indeterminacy of the Arabidopsis (Arabidopsis thaliana) primary root
Given the fact that lateral root development is considered to be a broad recapitulation of equivalent processes in the primary root, we investigated whether SHR plays a role in lateral root primordia (LRP) development and, on global root system architecture (RSA)
We initially investigated the morphological effect the shr mutation had on the development of the root system in soil

Summary

Introduction

SHORT-ROOT (SHR) is a well-characterized regulator of radial patterning and indeterminacy of the Arabidopsis (Arabidopsis thaliana) primary root. Arabidopsis (Arabidopsis thaliana) have a primary root that repeatedly branches to generate several orders of lateral roots, whereas the root systems of cereal crops such as rice (Oryza sativa) and maize (Zea mays) are predominantly composed of adventitious roots (Hochholdinger et al, 2004; Osmont et al, 2007) Despite these anatomical differences, with the exception of the highest orders, roots from all plant species exhibit indeterminate growth behavior (i.e. are able to maintain growth indefinitely; Waisel et al, 2002). The cellular basis of indeterminate root growth has been best studied in the Arabidopsis primary root In this experimental system, stem cells ( termed initials) abut specialized organizing cells (often denoted as the quiescent center [QC]) within the root apical meristem (RAM; Dolan et al, 1993).

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