Unraveling Root Developmental Programs Initiated by BeneficialPseudomonasspp. Bacteria

Christos Zamioudis,Ikram Blilou,Corné M.J Pieterse,Parthena Mastranesti,Pankaj Dhonukshe

doi:10.1104/pp.112.212597

Abstract

Plant roots are colonized by an immense number of microbes, referred to as the root microbiome. Selected strains of beneficial soil-borne bacteria can protect against abiotic stress and prime the plant immune system against a broad range of pathogens. Pseudomonas spp. rhizobacteria represent one of the most abundant genera of the root microbiome. Here, by employing a germ-free experimental system, we demonstrate the ability of selected Pseudomonas spp. strains to promote plant growth and drive developmental plasticity in the roots of Arabidopsis (Arabidopsis thaliana) by inhibiting primary root elongation and promoting lateral root and root hair formation. By studying cell type-specific developmental markers and employing genetic and pharmacological approaches, we demonstrate the crucial role of auxin signaling and transport in rhizobacteria-stimulated changes in the root system architecture of Arabidopsis. We further show that Pseudomonas spp.-elicited alterations in root morphology and rhizobacteria-mediated systemic immunity are mediated by distinct signaling pathways. This study sheds new light on the ability of soil-borne beneficial bacteria to interfere with postembryonic root developmental programs.

Highlights

Plant roots are colonized by an immense number of microbes, referred to as the root microbiome
Rhizobacteria-Induced Root Developmental Programs root system architecture is defined by three main processes: (1) indeterminate growth of the main root, a process orchestrated by the root meristem; (2) lateral root (LR) formation; and (3) root hair (RH) formation
Auxin gradients such as those established by the PIN-FORMED (PIN) auxin efflux facilitator network and a genetic program regulated by WUSCHEL-RELATED HOMEOBOX5 (WOX5), SCARECROW (SCR), SHORT-ROOT, and PLETHORA transcription factor proteins are crucial for stem cell maintenance and function (Di Laurenzio et al, 1996; Helariutta et al, 2000; Aida et al, 2004; Blilou et al, 2005; Sarkar et al, 2007)

Summary

Introduction

Plant roots are colonized by an immense number of microbes, referred to as the root microbiome. The population of mitotic cells in the root meristem originates from stem cells whose identity is controlled by an organizing center called the quiescent center (QC; Bennett and Scheres, 2010) Auxin gradients such as those established by the PIN-FORMED (PIN) auxin efflux facilitator network and a genetic program regulated by WUSCHEL-RELATED HOMEOBOX5 (WOX5), SCARECROW (SCR), SHORT-ROOT, and PLETHORA transcription factor proteins are crucial for stem cell maintenance and function (Di Laurenzio et al, 1996; Helariutta et al, 2000; Aida et al, 2004; Blilou et al, 2005; Sarkar et al, 2007). The expression of GL2 is reduced and the H fate is adopted by those cells (Schiefelbein, 2003; Ueda et al, 2005; Ishida et al, 2008; Grebe, 2012)

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Conclusion