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Protein disulfide isomerase (PDI) is a multifunctional enzyme that catalyzes rate-limiting reactions such as disulfide bond formation, isomerization, and reduction. There is some evidence that indicates that PDI is also involved in host-pathogen interactions in plants. In this study, we show that the rice root-knot nematode, <i>Meloidogyne graminicola</i>, has evolved a secreted effector, MgPDI2, which is expressed in the subventral esophageal glands and up-regulated during the early parasitic stage of <i>M. graminicola</i>. Purified recombinant MgPDI2 functions as an insulin disulfide reductase and protects plasmid DNA from nicking. As an effector, MgPDI2 contributes to nematode parasitism. Silencing of <i>MgPDI2</i> by RNA interference in the pre-parasitic second-stage juveniles (J2s) reduced <i>M. graminicola</i> multiplication and also increased <i>M. graminicola</i> mortality under H₂O₂ stress. In addition, an <i>Agrobacterium</i>-mediated transient expression assay found that MgPDI2 caused noticeable cell death in <i>Nicotiana benthamiana</i>. An intact C-terminal region containing the first catalytic domain (a) with an active motif (Cys-Gly-His-Cys, CGHC) and the two non-active domains (b and b′) is required for cell death induction in <i>N. benthamiana</i>. This research may provide a promising target for the development of new strategies to combat <i>M. graminicola</i> infections.