The nematode effector Mj-NEROSs interacts with Rieske's iron-sulfur protein influencing plastid ROS production to suppress plant immunity.

Root-knot nematodes (RKN; Meloidogyne species) are plant pathogens that introduce several effectors in their hosts to facilitate infection. The actual targets and functioning mechanism of these effectors largely remain unexplored. This study illuminates the role and interplay of the Meloidogyne javanica nematode effector ROS suppressor (Mj-NEROSs) within the host plant environment. Mj-NEROSs suppresses INF1-induced cell death as well as flg22-induced callose deposition and reactive oxygen species (ROS) production. A transcriptome analysis highlighted the downregulation of ROS-related genes upon Mj-NEROSs expression. NEROSs interacts with the plant Rieske's iron-sulfur protein (ISP) as shown by yeast-two-hybrid and bimolecular fluorescence complementation. Secreted from the subventral pharyngeal glands into giant cells, Mj-NEROSs localizes in the plastids where it interacts with ISP, subsequently altering electron transport rates and ROS production. Moreover, our results demonstrate that isp Arabidopsis thaliana mutants exhibit increased susceptibility to M. javanica, indicating ISP importance for plant immunity. The interaction of a nematode effector with a plastid protein highlights the possible role of root plastids in plant defense, prompting many questions on the details of this process.

Transcriptome Analysis of Meloidogyne javanica and the Role of a C-Type Lectin in Parasitism.

Meloidogyne javanica is one of the most widespread and economically important sedentary endoparasites. In this study, a comparative transcriptome analysis of M. javanica between pre-parasitic second-stage juveniles (Pre-J2) and parasitic juveniles (Par-J3/J4) was conducted. A total of 48,698 unigenes were obtained, of which 18,826 genes showed significant differences in expression (p < 0.05). In the differentially expressed genes (DEGs) from transcriptome data at Par-J3/J4 and Pre-J2, a large number of unigenes were annotated to the C-type lectin (CTL, Mg01965), the cathepsin L-like protease (Mi-cpl-1), the venom allergen-like protein (Mi-mps-1), Map-1 and the cellulase (endo-ß-1,4-glucanase). Among seven types of lectins found in the DEGs, there were 10 CTLs. The regulatory roles of Mj-CTL-1, Mj-CTL-2 and Mj-CTL-3 in plant immune responses involved in the parasitism of M. javanica were investigated. The results revealed that Mj-CTL-2 could suppress programmed cell death (PCD) triggered by Gpa2/RBP-1 and inhibit the flg22-stimulated ROS burst. In situ hybridization and developmental expression analyses showed that Mj-CTL-2 was specifically expressed in the subventral gland of M. javanica, and its expression was up-regulated at Pre-J2 of the nematode. In addition, in planta silencing of Mj-CTL-2 substantially increased the plant resistance to M. javanica. Moreover, yeast co-transformation and bimolecular fluorescence complementation assay showed that Mj-CTL-2 specifically interacted with the Solanum lycopersicum catalase, SlCAT2. It was demonstrated that M. javanica could suppress the innate immunity of plants through the peroxide system, thereby promoting parasitism.

A Bursaphelenchus xylophilus effector BxICD1 inducing plant cell death, concurrently contributes to nematode virulence and migration.

The migratory endoparasitic phytonematodes Bursaphelenchus xylophilus is the causal agent of pine wilt disease and causes significant economic damage to pine forests in China. Effectors play a key role in the successful parasitism of plants by phytonematodes. In this study, 210 genes obtained by transcriptomics analyses were found to be upregulated in B. xylophilus infecting Pinus massoniana that were not functionally annotated nor reported previously in B. xylophilus infecting P. thunbergii. Among these differentially expressed genes, a novel effector, BxICD1, that could induce cell death in the extracellular space of Nicotiana benthamiana was identified. BxICD1 was upregulated in the early stages of infection, as shown by RT-qPCR analyses. In situ hybridization analysis showed that BxICD1 was expressed in the esophageal gland of nematodes. The yeast signal sequence trap system indicated that BxICD1 possessed an N-terminal signal peptide with secretion functionality. Using an Agrobacterium-mediated transient expression system, it was demonstrated that the cell death-inducing activity of BxICD1 was dependent on N. benthamiana brassinosteroid-insensitive 1-associated kinase 1 (NbBAK1). Finally, BxICD1 contributed to B. xylophilus virulence and migration in host pine trees, as demonstrated by RNAi silencing assays. These findings indicate that BxICD1 both induces plant cell death and also contributes to nematode virulence and migration in P. massonian.