Abstract
Detection of conserved microbial patterns by host cell surface pattern recognition receptors (PRRs) activates innate immunity. The FLAGELLIN-SENSITIVE 2 (FLS2) receptor perceives bacterial flagellin and recruits another PRR, BAK1 and the cytoplasmic-kinase BIK1 to form an active co-receptor complex that initiates antibacterial immunity in Arabidopsis. Molecular mechanisms that transmit flagellin perception from the plasma-membrane FLS2-associated receptor complex to intracellular events are less well understood. Here, we show that flagellin induces the conjugation of the SMALL UBIQUITIN-LIKE MODIFIER (SUMO) protein to FLS2 to trigger release of BIK1. Disruption of FLS2 SUMOylation can abolish immune responses, resulting in susceptibility to bacterial pathogens in Arabidopsis. We also identify the molecular machinery that regulates FLS2 SUMOylation and demonstrate a role for the deSUMOylating enzyme, Desi3a in innate immunity. Flagellin induces the degradation of Desi3a and enhances FLS2 SUMOylation to promote BIK1 dissociation and trigger intracellular immune signalling.
Highlights
Detection of conserved microbial patterns by host cell surface pattern recognition receptors (PRRs) activates innate immunity
In this study we demonstrate that SUMOylation of FLAGELLIN-SENSITIVE 2 (FLS2) is enhanced upon flagellin perception and this modification facilitates its dissociation from BIK1
In a proteomic screen using transgenic plants expressing streptavidin tagged SUMO1 to identify SUMOylated proteins during flg22triggered immune responses, we identified peptide fragments that match FLS2, suggesting that this receptor might be a potential target for SMALL UBIQUITIN-LIKE MODIFIER (SUMO) conjugation (Supplementary Table 1)
Summary
Detection of conserved microbial patterns by host cell surface pattern recognition receptors (PRRs) activates innate immunity. The FLAGELLIN-SENSITIVE 2 (FLS2) receptor perceives bacterial flagellin and recruits another PRR, BAK1 and the cytoplasmic-kinase BIK1 to form an active co-receptor complex that initiates antibacterial immunity in Arabidopsis. Molecular mechanisms that transmit flagellin perception from the plasma-membrane FLS2-associated receptor complex to intracellular events are less well understood. Flagellin induces the degradation of Desi3a and enhances FLS2 SUMOylation to promote BIK1 dissociation and trigger intracellular immune signalling. BIK1 is directly phosphorylated by BAK113,14 and dissociates from FLS2 in a BAK1 dependent manner to activate downstream signalling components This includes activation of mitogenactivated protein kinases (MAPKs) and respiratory burst oxidase homologue protein D (RbohD) to generate a burst of reactive oxygen species (ROS)[12,17] to trigger immune signalling, which potentially halts the pathogen before it establishes within the plant host. We identify a class of membrane-localized SUMO proteases that are able to target the FLS2 receptor for deSUMOylation to regulate immune signalling
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