Salicylic Acid Is Required for Broad-Spectrum Disease Resistance in Rice.

Bingbing Liang,Xujun Chen,Ce Yang,Han Wang,Zejian Guo,Linlu Qi,Luyao Wang

doi:10.3390/ijms23031354

Bingbing Liang, Xujun Chen + Show 5 more

Open Access

https://doi.org/10.3390/ijms23031354

Copy DOI

Abstract

Rice plants contain high basal levels of salicylic acid (SA), but some of their functions remain elusive. To elucidate the importance of SA homeostasis in rice immunity, we characterized four rice SA hydroxylase genes (OsSAHs) and verified their roles in SA metabolism and disease resistance. Recombinant OsSAH proteins catalyzed SA in vitro, while OsSAH3 protein showed only SA 5-hydroxylase (SA5H) activity, which was remarkably higher than that of other OsSAHs that presented both SA3H and SA5H activities. Amino acid substitutions revealed that three amino acids in the binding pocket affected SAH enzyme activity and/or specificity. Knockout OsSAH2 and OsSAH3 (sahKO) genes conferred enhanced resistance to both hemibiotrophic and necrotrophic pathogens, whereas overexpression of each OsSAH gene increased susceptibility to the pathogens. sahKO mutants showed increased SA and jasmonate levels compared to those of the wild type and OsSAH-overexpressing plants. Analysis of the OsSAH3 promoter indicated that its induction was mainly restricted around Magnaporthe oryzae infection sites. Taken together, our findings indicate that SA plays a vital role in immune signaling. Moreover, fine-tuning SA homeostasis through suppression of SA metabolism is an effective approach in studying broad-spectrum disease resistance in rice.

Highlights

Plants have a sophisticated defense system against pathogen invasion
OsSAH recombinant proteins purified from Escherichia coli were tested for enzymatic activity using salicylic acid (SA), benzoic acid (BA), trans-cinnamic acid (tCA), or caffeic acid as substrates
We examined whether OsSAH genes were involved in resistance to the hemibiotrophic Xanthomonas oryzae pv. oryzae (Xoo) J18 strain, which causes the bacterial leaf blight

Summary

Introduction

A general defense is the pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI), initiated by the recognition of PAMPs via pattern recognition receptors (PRRs) [1]. A more specific defense is the effector-triggered immunity (ETI), activated by host resistance genes that recognize effectors secreted by pathogens to suppress PTI. Phytohormones, such as salicylic acid (2-hydroxy benzoic acid, SA) and jasmonic acid (JA), are important compounds in the immune signaling pathways. Chorismate is converted to isochorismate by isochorismate synthase (ICS). Arabidopsis genome contains two ICS genes, responsible for 90% of SA synthesis under stimulation by pathogen challenge or UV radiation [4]. Phenylalanine, derived from chorismate, can be converted into SA through the phenylpropanoid biosynthesis pathway. Phenylalanine ammonia-lyase (PAL) catalyzes the conversion of Phe to trans-cinnamic acid (tCA), which is oxidized to benzoic acid (BA)

Methods

Results

Conclusion