Receptor-like kinase SOBIR1/EVR interacts with receptor-like proteins in plant immunity against fungal infection

Abstract

The plant immune system is activated by microbial patterns that are detected as nonself molecules. Such patterns are recognized by immune receptors that are cytoplasmic or localized at the plasma membrane. Cell surface receptors are represented by receptor-like kinases (RLKs) that frequently contain extracellular leucine-rich repeats and an intracellular kinase domain for activation of downstream signaling, as well as receptor-like proteins (RLPs) that lack this signaling domain. It is therefore hypothesized that RLKs are required for RLPs to activate downstream signaling. The RLPs Cf-4 and Ve1 of tomato ( Solanum lycopersicum ) mediate resistance to the fungal pathogens Cladosporium fulvum and Verticillium dahliae , respectively. Despite their importance, the mechanism by which these immune receptors mediate downstream signaling upon recognition of their matching ligand, Avr4 and Ave1, remained enigmatic. Here we show that the tomato ortholog of the Arabidopsis thaliana RLK Suppressor Of BIR1-1/Evershed (SOBIR1/EVR) and its close homolog S. lycopersicum ( Sl )SOBIR1-like interact in planta with both Cf-4 and Ve1 and are required for the Cf-4– and Ve1-mediated hypersensitive response and immunity. Tomato SOBIR1/EVR interacts with most of the tested RLPs, but not with the RLKs FLS2, SERK1, SERK3a, BAK1, and CLV1. SOBIR1/EVR is required for stability of the Cf-4 and Ve1 receptors, supporting our observation that these RLPs are present in a complex with SOBIR1/EVR in planta . We show that SOBIR1/EVR is essential for RLP-mediated immunity and propose that the protein functions as a regulatory RLK of this type of cell-surface receptors.

Fungal Endopolygalacturonases Are Recognized as Microbe-Associated Molecular Patterns by the Arabidopsis Receptor-Like Protein RESPONSIVENESS TO BOTRYTIS POLYGALACTURONASES1

“…The RLK SOBIR1 was initially identified as a suppressor of BIR1 that regulates cell death (Gao et al, 2009). More recent studies show that tomato SOBIR1 particularly interacts with LRR-RLPs that play a role in defense against fungal pathogens (Liebrand et al, 2013). Experiments presented here show that Arabidopsis SOBIR1 interacts with RBPG1 and is essential for RBPG1-mediated responsiveness to PGs.…”

“…The current paradigm for signaling via RLPs is heterodimerization with RLKs (Bleckmann et al, 2010;Liebrand et al, 2013). The RLK SOBIR1 was initially identified as a suppressor of BIR1 that regulates cell death (Gao et al, 2009).…”

“…Recently, the tomato LRR-RLK SOBIR1 was shown to interact specifically with a number of LRR-RLPs (Liebrand et al, 2013). To test whether LRR-RLKs are involved in the response of RBPG1 to BcPG3, Arabidopsis plants carrying mutations in different LRR-RLK genes were analyzed (Fig.…”

“…SOBIR1 does not physically interact with BIR1, suggesting that SOBIR1 mediates an alternative signal transduction route. A recent study showed that the tomato SOBIR1 interacts with RLPs and is required for RLP-mediated disease resistance (Liebrand et al, 2013).…”

New insights into receptor-like protein functions in Arabidopsis

“…It has been demonstrated that SOBIR1 physically interacted with Cf-4, Ve1, LepR3, Rlm2, AtRLP1, AtRLP23, AtRLP30 and AtRLP42, and was required for the proper function of these RLPs. 9,10,12,13,15,16,[24][25][26] However, it is unclear about the biological relevance of the physical interaction between SOBIR1 and two developmental RLPs CLV2 and TMM, respectively. It could postulate that SOBIR1 may involve in the CLV2-and/or TMM-mediated developmental processes.…”