Together with our previous report earlier this year (Yu et al, PLoS Pathogens, 2025), this work suggests that hijacking plant kinases is an important strategy for bacterial effectors to promote their own phosphorylation and stability in plant cells

doi.org/10.1371/jour...

These phosphorylation sites seem to be important for RipBM contribution to virulence in tomato, reflecting an effector strategy to promote its own stability and contribute to bacterial virulence

However, RipBM is phosphorylated by SnRK-family proteins in plant cells and subsequently associates with plant 14-3-3 proteins, which prevent RipBM ubiquitination and degradation

RipBM is an unconventional type-III effector from Ralstonia, in the sense that it encodes a kinase domain, although, in our experience, kinase activity is not detectable. Sustained RipBM expression in eukaryotic cells leads to cell death, which seems to be a toxic effect of RipBM activity

My guess is it forms an “imperfect” complex that mediates a different type of recognition of flg22Rso and a subsequent activation that does engage all the usual downstream targets, but only some of them

This reminds me the treatments with the flg22G/A mutant peptide we did in Sun et al, Science, 2013 (doi.org/10.1126/scie...). That mutation abolishes BAK1 interaction and activation, significantly reduces ROS, but does not affect MAPK activation

Hopefully, the information that heterologous PRR expression can confer novel PAMP recognition could provide new information for the design of synthetic immune receptors with expanded recognition of polymorphic pathogen elicitors

Long story short, it seems that AtFLS2, when expressed in N. benthamiana, associates with NbSERKs and mediate a “partial” complex activation that leads to some downstream responses (MAPK, gene expression), but not others (ROS). Eventually, this enhances disease resistance

We did not see any gain of flg22Rso-triggered ROS burst, but…

there was MAPK activation. Surprisingly, what was supposed to be a “negative control”, even WT AtFLS2 expressed in N. benthamiana would confer MAPK activation upon flg22Rso treatment

Before, we identified 2 residues in soybean FLS2 that contribute to the gain of recognition of the polymorphic Ralstonia flg22 (see attached paper)
doi.org/10.1038/s414...

Then we tried to see if mutating the equivalent residues in Arabidopsis FLS2 would confer recognition