The oomycete effector-targeted nuclear envelope protein StKAKU4 negatively regulates plant immunity via vesicle trafficking

Nucleoskeleton proteins modulate nuclear structure and play important roles in diverse cellular processes. Yet, their functions in immune responses are poorly understood. Here, we report that a nucleoskeleton protein, potato lamin-like protein StKAKU4, is targeted and stabilized by the oomycete RxLR effector Pi22798 to suppress immunity. StKAKU4 predominantly localizes to the nuclear envelope (NE) and is frequently trafficked between the NE and endosomal organelles. Enhanced expression of KAKU4 in Nicotiana benthamiana significantly increases Phytophthora infestans infection, whereas silencing of KAKU4 in potato and N. benthamiana enhances resistance, suggesting that it acts as a susceptibility (S) factor. GFP-StKAKU4 accumulates at the extrahaustorial membrane (EHM) during P. infestans infection. Moreover, Pi22798 interacts with StKAKU4 at the NE and accelerates endomembrane trafficking of StKAKU4 to the cytoplasm. An endomembrane enrichment assay indicates that StKAKU4 is involved in intracellular transport. In the immunopurified GFP-StKAKU4-associated endomembrane proteome, both host immunity-associated proteins and several P. infestans RxLR effectors are enriched, whereas apoplastic effectors such as PiSCR74, which do not enter host cells, are not. Our findings reveal a mechanism by which the potato NE protein StKAKU4 is involved in vesicle trafficking and is exploited by P. infestans to facilitate infection and colonization, offering valuable insights into S factors and potential strategies for improving disease resistance.