The role of photoprotection in defence of two wheat genotypes against Zymoseptoria tritici

Olubukola O Ajigboye,Dasuni P Jayaweera,Alexander V Ruban,Victoria Pastor,Erik H Murchie,Richard Summers,Dimitra Angelopoulou,Rumiana V Ray

doi:10.1111/ppa.13392

Abstract

AbstractThis study provides new insights into the role of photoprotection in preformed and induced defence of two wheat genotypes with contrasting phenotypes to infection by Zymoseptoria tritici. We investigated the mechanisms of the photoprotective response during early infection, including nonphotochemical quenching (NPQ), β‐carotene‐derived xanthophylls, reactive oxygen species, and the phytohormones abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA). Furthermore, we quantified the effects of pathogenesis on photosynthesis, stomatal control, and expression of plant defence molecular markers. The photoprotective mechanism of successful defence involved the qI component of NPQ leading to rapid down‐regulation of photosystem II quantum yield and chlorophyll a:b, increased biosynthesis of the xanthophyll neoxanthin and ABA, and the expression of chloroplast‐specific enzymes to engage in scavenging of O2●−. Elevated ABA in the resistant genotype correlated with preformed leaf defence traits including low stomatal density, increased expression of wax biosynthesis, and lignification. Z. tritici exhibited reduced germination and branching on the resistant host genotype and hijacked stomatal control in both genotypes by enhancing stomatal sensitivity to light. Increased biosynthesis of JA and anthocyanins, in contrast to SA, were quantified in the incompatible interaction. Our results indicate that ABA and JA in antagonistic action to SA were associated with defence in the resistant genotype, Cougar, against Z. tritici.

Highlights

Zymoseptoria tritici is one of the most important fungal pathogens of wheat causing Septoria tritici blotch (STB)
Silencing two key chloroplast genes involved in the carotenoid and chlorophyll biosynthesis, phytoene desaturase and Mg-chelatase H subunit, respectively, rendered Stb6-mediated resistance in wheat to Z. tritici partially compromised; this resulted in increased susceptibility and programmed cell death (PCD) associated with excessive superoxide and hydrogen peroxide accumulation (Lee et al, 2015)
We have shown two contrasting photoprotection responses of wheat genotypes but only one of them was associated with enhanced defence against Z. tritici

Summary

| INTRODUCTION

Zymoseptoria tritici is one of the most important fungal pathogens of wheat causing Septoria tritici blotch (STB). Silencing two key chloroplast genes involved in the carotenoid and chlorophyll biosynthesis, phytoene desaturase and Mg-chelatase H subunit, respectively, rendered Stb6-mediated resistance in wheat to Z. tritici partially compromised; this resulted in increased susceptibility and PCD associated with excessive superoxide and hydrogen peroxide accumulation (Lee et al, 2015). These results strongly suggest that the inability of the host to regulate oxidative stress via the chloroplast is probably exploited by the pathogen to overcome host defence. We characterized the physiology of responses during the transition to the symptomatic phase of the disease to show the effects of compatible and incompatible interactions on stomatal conductance, photosynthesis, and chlorophyll fluorescence

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION