NPR1 Protein Regulates Pathogenic and Symbiotic Interactions between Rhizobium and Legumes and Non-Legumes

Smadar Peleg-Grossman,Yuval Kaye,Yael Golani,Naomi Melamed-Book,Alex Levine,Karin Schumacher

doi:10.1371/journal.pone.0008399

Smadar Peleg-Grossman, Yuval Kaye + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0008399

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Journal: PloS one	Publication Date: Dec 21, 2009
Citations: 95	License type: CC BY 4.0

Affiliation: Hebrew University of Jerusalem

Abstract

BackgroundLegumes are unique in their ability to establish symbiotic interaction with rhizobacteria from Rhizobium genus, which provide them with available nitrogen. Nodulation factors (NFs) produced by Rhizobium initiate legume root hair deformation and curling that entrap the bacteria, and allow it to grow inside the plant. In contrast, legumes and non-legumes activate defense responses when inoculated with pathogenic bacteria. One major defense pathway is mediated by salicylic acid (SA). SA is sensed and transduced to downstream defense components by a redox-regulated protein called NPR1.Methodology/Principal FindingsWe used Arabidopsis mutants in SA defense pathway to test the role of NPR1 in symbiotic interactions. Inoculation of Sinorhizobium meliloti or purified NF on Medicago truncatula or nim1/npr1 A. thaliana mutants induced root hair deformation and transcription of early and late nodulins. Application of S. meliloti or NF on M. truncatula or A. thaliana roots also induced a strong oxidative burst that lasted much longer than in plants inoculated with pathogenic or mutualistic bacteria. Transient overexpression of NPR1 in M. truncatula suppressed root hair curling, while inhibition of NPR1 expression by RNAi accelerated curling.Conclusions/SignificanceWe show that, while NPR1 has a positive effect on pathogen resistance, it has a negative effect on symbiotic interactions, by inhibiting root hair deformation and nodulin expression. Our results also show that basic plant responses to Rhizobium inoculation are conserved in legumes and non-legumes.

Highlights

Plants continually interact with soil micro-organisms that are broadly divided into pathogenic, saprophytic or symbiotic
Conclusions/Significance: We show that, while NPR1 has a positive effect on pathogen resistance, it has a negative effect on symbiotic interactions, by inhibiting root hair deformation and nodulin expression
While the pathogenic and saprophytic interactions are common to all plant species, symbiosis with the nitrogen-fixing rhizobacteria is a relatively recent evolutionary development that is restricted to plants of the legumes family

Summary

Introduction

Plants continually interact with soil micro-organisms that are broadly divided into pathogenic, saprophytic or symbiotic. Legumes are unique in their ability to establish symbiotic interaction with rhizobacteria from the Rhizobium genus, which provide plants with a source of available nitrogen. Symbiosis between legumes and Rhizobium is initiated by specific nodulation (Nod) factors (NFs) that are secreted into the soil by the bacteria. The root cells in the cortex undergo reprogramming and begin to divide rapidly, giving rise to a nodule primordium, a specific plant organ that provides favorable environment for nitrogen fixation by Rhizobium [2]. Legumes are unique in their ability to establish symbiotic interaction with rhizobacteria from Rhizobium genus, which provide them with available nitrogen. Nodulation factors (NFs) produced by Rhizobium initiate legume root hair deformation and curling that entrap the bacteria, and allow it to grow inside the plant. SA is sensed and transduced to downstream defense components by a redox-regulated protein called NPR1

Methods

Conclusion