The root-knot nematode effector MiPDI1 targets a stress-associated protein, SAP, to establish disease in Solanaceae and Arabidopsis.

Large amounts of effectors are secreted by the oesophageal glands of plant-parasitic nematodes, but their molecular mode of action remains largely unknown. We characterised a Meloidogyne incognita protein disulphide isomerase (PDI)-like effector protein (MiPDI1) that facilitates nematode parasitism. In situ hybridisation showed that MiPDI1 was expressed specifically in the subventral glands of M. incognita. It was significantly upregulated during parasitic stages. Immunolocalisation demonstrated MiPDI1 secretion in planta during nematode migration and within the feeding cells. Host-induced silencing of the MiPDI1 gene affected the ability of the nematode to infect the host, whereas MiPDI1 expression in Arabidopsis increased susceptibility to M. incognita, providing evidence for a key role of MiPDI1 in M. incognita parasitism. Yeast two-hybrid assays, BiFC and Co-IP showed that MiPDI1 interacted with a tomato stress-associated protein (SlSAP12) orthologous to the redox-regulated AtSAP12, which plays an important role in plant responses to abiotic and biotic stresses. SAP12 silencing or knocking out in N. benthamiana and Arabidopsis increased susceptibility to M. incognita. Our results suggest that MiPDI1 acts as a pathogenicity factor promoting disease by fine-tuning SAP-mediated responses at the interface of redox signalling, defence and stress acclimation in Solanaceae and Arabidopsis.