StBPA1 attenuates surface receptor activation and finely regulates immune responses against bacterial and oomycete...

Plants utilize plasma-membrane-localized pattern recognition receptors (PRRs) to sense and respond to microbial infections. The downstream regulatory components have been studied extensively, but the mechanisms ensuring appropriate immune responses to diverse pathogens remain enigmatic. We report that a core regulatory component named StBPA1 (BINDING PARTNER OF ACD11) is a molecular switch that controls both anti-bacterial and anti-oomycete immunity. StBPA1-knockout displays dwarfed growth, enhanced pattern-triggered immunity (PTI), and broad-spectrum resistance to potato bacterial wilt and late blight diseases. StBPA1 negatively regulates the FLAGELLIN SENSING 2 (StFLS2)-BRI1-ASSOCIATED KINASE 1 (StBAK1)/SUPPRESSOR OF BIR1-1 (StSOBIR1)-StBAK1 immune complex formation and inhibits StFLS2 kinase activity to prevent constitutive immune responses. In turn, StBAK1 specifically phosphorylates StBPA1 at Thr¹⁹³/Ser¹⁹⁵. This modification is enhanced by flg22/INF1 perception and impairs the negative regulatory role of StBPA1, thereby ensuring proper immune signaling. These findings identify an StBPA1-PRR complex regulatory module and highlight inhibitions by StBPA1 as key mechanisms to ensure efficient yet strictly regulated immune responses against different pathogens.