A rapid influx of cytosolic Ca²⁺ is a critical early event in PAMP-triggered immunity (PTI), largely mediated by cyclic nucleotide-gated channels (CNGCs). However, the regulation of these channels remains poorly understood. We discovered that the Phytophthora infestans RXLR effector AVRblb2 interferes with PTI by targeting NbCNGC18, a calcium channel essential for immune signaling. AVRblb2 forms a ternary complex with calmodulin (CaM)/calmodulin-like proteins (CMLs) and NbCNGC18, stabilizing the inactive CaM/CML–CNGC complex and preventing channel activation. This disrupts Ca²⁺ influx and suppresses downstream immune responses. Notably, virus-induced silencing of multiple NbCNGCs diminishes the virulence-promoting effect of AVRblb2, confirming CNGCs as its functional targets. Interestingly, we also found that NbCNGC18 contributes to ETI by associating with the NLR receptor Rpiblb2 and helper NLR NRC4, suggesting that AVRblb2 may impair both PTI and ETI through distinct modes of interference. These findings reveal a novel effector strategy that hijacks host calcium signaling hubs to suppress layered plant immunity.
