The Nuclear Effector MiISE23 From <i>Meloidogyne incognita</i> Targets JAZ Proteins and Suppresses Jasmonate Signalling, Increasing Host Susceptibility

Meloidogyne incognita is an economically important plant-parasitic nematode that can infect thousands of different plant species. During its interaction with host plants, M. incognita synthesises numerous effectors in oesophageal glands, which are then secreted into plant tissues. Here, we characterised the effector MiISE23 and found that it could suppress plant immune responses. In situ hybridisation showed that MiISE23 was expressed in the subventral glands. Transgenic Arabidopsis plants expressing MiISE23 were more susceptible to M. incognita, whereas host-derived RNAi of MiISE23 was found to decrease M. incognita infection in Arabidopsis. In vitro and in vivo experiments showed that MiISE23 repressed jasmonate (JA) signalling by directly interacting with and suppressing jasmonoyl-isoleucine (JA-Ile)-induced degradation of jasmonate ZIM-domain proteins by COI1. The expression of MiISE23 in Arabidopsis repressed the expression of JA-responsive genes and reduced the levels of endogenous JA-Ile. AtJAZ6 transgenic lines of Arabidopsis showed increased susceptibility to M. incognita infection. Collectively, our results show that MiISE23 stabilises JAZ proteins and interferes with JA signalling, revealing a novel mechanism utilised by root-knot nematodes to hijack phytohormone signalling and promote parasitism.