Identification of a novel receptor of bacterial PAMP RsE in Arabidopsis using genomic tools

Abstract

Plant innate immunity is triggered when a pathogen invades the cell and pathogen associated molecular patterns (PAMPs) are recognized by plant pattern recognition receptors (PRRs). Contrasting to the large amount of PAMPs identified so far, only a limited number of PRRs are known. RsE2 is a novel PAMP that was partially purified from the bacterial pathogen, Ralstonia solanacearum (Melzer, 2013). This pathogen colonizes xylem of plants and causes wilt in a wide range of host species. RsE2 could be effectively identified and elicits several early immunity responses such as ethylene response, oxidative burst in the plants and extracellular alkalization in cell suspensions of Arabidopsis thaliana. Further studies disclosed substantial natural variation in the RsE2-mediated ethylene response among different ecotypes of Arabidopsis thaliana. I hypothesized that the genetic variation in the RsE2-recognizing PRR gene in ecotypes is responsible for the phenotypical variation in the RsE2- caused response. To identify the RsE2-recognizing PRRs, I screened for RsE2-induced/triggered ethylene response in multiple Arabidopsis thaliana ecotypes and conducted a genome wide associated study (GWAS). Meanwhile, I developed a F2 mapping population. Using a NGS-assisted (Next Generation Sequencing) QTL (Quantitative Trait Locus) mapping approach, I mapped RsE2 sensitivity to an 1.1 Mb region on Chr 3. This region overlaps with one of four candidate framed in GWAS as significant. Forward genetic analysis further identified that receptor like protein RLP32 is the receptor of RsE2 in Arabidopsis. My work showed great advantages to identify the RsE2-recognizing PRR using genomic tools. Furthermore, I showed that RLP32-mediated RsE2 perception was compromised in the bak1/bkk1 double mutant or sobir1 mutant. The RLP32/Bak1/SOBIR1 tripartite-receptor provides a good system to study how a RLP-type PRR mediates signal transduction during PAMP-triggered immunity (PTI). Finally, the transient expression of RLP32 from Brassiaceae plant family in N. benthamiana seedling could confer the capability of elicitor perception in Solanaceae plant family, which suggests the potential application of engineered RsE2-recognizing system to enhance plant disease resistance.