PRR2, a pseudo-response regulator, promotes salicylic acid and camalexin accumulation during plant immunity

C Cheval,A Mithöfer,E Robe,J P Galaud,M Perez,A Perochon,D Aldon,C Mazars,M Reichelt,B Ranty,L J Leba

doi:10.1038/s41598-017-07535-8

Abstract

Calcium signalling mediated by Calmodulin (CaM) and calmodulin-like (CML) proteins is critical to plant immunity. CaM and CML regulate a wide range of target proteins and cellular responses. While many CaM-binding proteins have been identified, few have been characterized for their specific role in plant immunity. Here, we report new data on the biological function of a CML-interacting partner, PRR2 (PSEUDO-RESPONSE REGULATOR 2), a plant specific transcription factor. Until now, the physiological relevance of PRR2 remained largely unknown. Using a reverse genetic strategy in A. thaliana, we identified PRR2 as a positive regulator of plant immunity. We propose that PRR2 contributes to salicylic acid (SA)-dependent responses when challenged with the phytopathogenic bacterium Pseudomonas syringae. PRR2 is transcriptionally upregulated by SA and P. syringae, enhances SA biosynthesis and SA signalling responses; e.g. in response to P. syringae, PRR2 induces the production of SA and the accumulation of the defence-related protein PR1. Moreover, PRR2 overexpressing lines exhibit an enhanced production of camalexin, a phytoalexin that confers enhanced resistance against pathogens. Together, these data reveal the importance of PRR2 in plant immune responses against P. syringae and suggest a novel function for this particular plant specific transcription factor in plant physiology.

Highlights

Plants have a great potential to adapt their growth and development to environmental changes
We generated independent transgenic plants carrying the ProPRR2::uidA gene fusion composed of a 2.3 kb region upstream of the start codon of PRR2 coding sequence fused to the GUS reporter gene
Significant expression of ProPRR2::uidA was detected in young leaves (Fig. 1C to E) with a strong GUS staining associated to the vasculature (Fig. 1C,E and G) and in epidermal specialized leaf structures such as guard cells (Fig. 1F)

Summary

Introduction

Plants have a great potential to adapt their growth and development to environmental changes This phenotypic plasticity relies on the ability to simultaneously integrate a wide variety of abiotic stimuli (light, temperature, nutrients...) and biotic interactions (pathogens, symbionts and others), through a network of signalling pathways mediated by second messengers and phytohormones. Downstream of these complex signalling networks, a multitude of transcription factors (TFs) regulate the expression of stress-responsive genes.

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Conclusion