Low Red/Far-Red Ratios Reduce Arabidopsis Resistance toBotrytis cinereaand Jasmonate Responses via a COI1-JAZ10-Dependent, Salicylic Acid-Independent Mechanism

Ignacio Cerrudo,Corné M.J Pieterse,Carlos L Ballaré,Patricia V Demkura,Mieke De Wit,Ronald Pierik,Micaela S Patitucci,Mercedes M Keller,Miriam D Cargnel

doi:10.1104/pp.112.193359

Abstract

Light is an important modulator of plant immune responses. Here, we show that inactivation of the photoreceptor phytochrome B (phyB) by a low red/far-red ratio (R:FR), which is a signal of competition in plant canopies, down-regulates the expression of defense markers induced by the necrotrophic fungus Botrytis cinerea, including the genes that encode the transcription factor ETHYLENE RESPONSE FACTOR1 (ERF1) and the plant defensin PLANT DEFENSIN1.2 (PDF1.2). This effect of low R:FR correlated with a reduced sensitivity to jasmonate (JA), thus resembling the antagonistic effects of salicylic acid (SA) on JA responses. Low R:FR failed to depress PDF1.2 mRNA levels in a transgenic line in which PDF1.2 transcription was up-regulated by constitutive expression of ERF1 in a coronatine insensitive1 (coi1) mutant background (35S::ERF1/coi1). These results suggest that the low R:FR effect, in contrast to the SA effect, requires a functional SCFCOI1-JASMONATE ZIM-DOMAIN (JAZ) JA receptor module. Furthermore, the effect of low R:FR depressing the JA response was conserved in mutants impaired in SA signaling (sid2-1 and npr1-1). Plant exposure to low R:FR ratios and the phyB mutation markedly increased plant susceptibility to B. cinerea; the effect of low R:FR was (1) independent of the activation of the shade-avoidance syndrome, (2) conserved in the sid2-1 and npr1-1 mutants, and (3) absent in two RNA interference lines disrupted for the expression of the JAZ10 gene. Collectively, our results suggest that low R:FR ratios depress Arabidopsis (Arabidopsis thaliana) immune responses against necrotrophic microorganisms via a SA-independent mechanism that requires the JAZ10 transcriptional repressor and that this effect may increase plant susceptibility to fungal infection in dense canopies.

Highlights

Light is an important modulator of plant immune responses
We tested the effects of low R:FR treatments on defense responses elicited by B. cinerea in fully deetiolated, soil-grown Arabidopsis rosettes
Reduction of R: FR ratio was achieved by supplementing the main light source with FR radiation, without altering the levels of photosynthetically active radiation (PAR), which produced a realistic simulation of the effect of the proximity of neighboring plants (Izaguirre et al, 2006; Moreno et al, 2009)

Summary

Introduction

We show that inactivation of the photoreceptor phytochrome B (phyB) by a low red/far-red ratio (R:FR), which is a signal of competition in plant canopies, down-regulates the expression of defense markers induced by the necrotrophic fungus Botrytis cinerea, including the genes that encode the transcription factor ETHYLENE RESPONSE FACTOR1 (ERF1) and the plant defensin PLANT DEFENSIN1.2 (PDF1.2). Low R:FR failed to depress PDF1.2 mRNA levels in a transgenic line in which PDF1.2 transcription was up-regulated by constitutive expression of ERF1 in a coronatine insensitive (coi1) mutant background (35S::ERF1/coi1) These results suggest that the low R:FR effect, in contrast to the SA effect, requires a functional SCFCOI1-JASMONATE ZIMDOMAIN (JAZ) JA receptor module. The light environment, which can be strongly affected by canopy density, is emerging as a critical regulator of JA signaling (Moreno et al, 2009; Demkura et al, 2010; Radhika et al, 2010; Robson et al, 2010; Suzuki et al, 2011) and plant defense (for review, see Roberts and Paul, 2006; Ballare, 2011; Kazan and Manners, 2011)

Methods

Results

Conclusion