Broad-Spectrum Disease Resistance Conferred by the Overexpression of Rice RLCK BSR1 Results from an Enhanced Immune Response to Multiple MAMPs.

Yasukazu Kanda,Yoko Nishizawa,Hitoshi Nakagawa,Takashi Kamakura,Masaki Mori

doi:10.3390/ijms20225523

Abstract

Plants activate their immune system through intracellular signaling pathways after perceiving microbe-associated molecular patterns (MAMPs). Receptor-like cytoplasmic kinases mediate the intracellular signaling downstream of pattern-recognition receptors. BROAD-SPECTRUM RESISTANCE 1 (BSR1), a rice (Oryza sativa) receptor-like cytoplasmic kinase subfamily-VII protein, contributes to chitin-triggered immune responses. It is valuable for agriculture because its overexpression confers strong disease resistance to fungal and bacterial pathogens. However, it remains unclear how overexpressed BSR1 reinforces plant immunity. Here we analyzed immune responses using rice suspension-cultured cells and sliced leaf blades overexpressing BSR1. BSR1 overexpression enhances MAMP-triggered production of hydrogen peroxide (H2O2) and transcriptional activation of the defense-related gene in cultured cells and leaf strips. Furthermore, the co-cultivation of leaves with conidia of the blast fungus revealed that BSR1 overexpression allowed host plants to produce detectable oxidative bursts against compatible pathogens. BSR1 was also involved in the immune responses triggered by peptidoglycan and lipopolysaccharide. Thus, we concluded that the hyperactivation of MAMP-triggered immune responses confers BSR1-mediated robust resistance to broad-spectrum pathogens.

Highlights

Plants combat pathogens by activating their innate immunity
BROAD-SPECTRUM RESISTANCE 1 (BSR1) overexpression did not increase transcript levels of RbohB, encoding a NADPH oxidase related to reactive oxygen species (ROS) burst (Supplementary Materials Figure S4). These results suggest that an excess of BSR1 protein could constitutively promote NADPH oxidase activity of RESPIRATORY BURST OXIDASE HOMOLOG (RBOH) proteins but not their transcription
DisBcSuRss1i,oan receptor-like cytoplasmic kinase (RLCK)-VII member, has a protein kinase activity and is important for the initiation of deBfSeRns1e, areRspLoCnKs-eVs IaIgmaienmstbcehr,ithinasolaigpormoterins, kinnoawsenaacstivaiftuynagnuds-ids eirmivpeodrtManAt MforPt[h3e9,i4n0i]t.iaBtiSoRn1oifs dimefpenlisceaterdesipnornesiesstaangcaeitnosbt acchteitriina,oalsigwoemllearssf,uknngoi,winnwaislda-tyfpuenganuds-odveerrivexepdreMssAinMgPric[e3l9i,n4e0s].[3B6S,3R81,40is], ismupglgiecastiendgitnharteBsiSsRta1nciseatlosobiancvteorlviae,daisnwreeslpl oanssfeusntrgiig, gienrewdilbdy-tbyapcetearniudmo-vdereivxepdreMssAinMg Prisc.eInlintheiss study, our experiments on suspension-cultured rice cells showed a correlation between BSR1 and the response to two bacterial elicitors, peptidoglycan and LPS

Summary

Introduction

Plants combat pathogens by activating their innate immunity. Microbe/pathogen-associated molecular patterns (MAMPs/PAMPs), which have molecular structures that are conserved in fungi or bacteria, alert plants to pathogen attacks. MAMPs are perceived by corresponding pattern-recognition receptors (PRRs) on host cell surfaces [2]. PRR complexes activate pattern-triggered immunity (PTI) through intracellular signaling pathways. Host-derived ROS play various roles in PTI. They possess an antimicrobial activity that can kill microbes, and they enhance physical barrier production by promoting lignin synthesis and cross-linking of plant cell walls [12,13,14,15]. Hydrogen peroxide (H2O2), an ROS produced in oxidative bursts, acts as a signaling molecule to induce the transcriptional activation of defense-related genes, biosynthesis of phytoalexin, and programmed cell death [11,16]

Methods

Results

Conclusion