A novel Meloidogyne graminicola effector, MgGPP, is secreted into host cells and undergoes glycosylation in concert with proteolysis to suppress plant defenses and promote parasitism

Abstract

Plant pathogen effectors can recruit the host post-translational machinery to mediate their post-translational modification (PTM) and regulate their activity to facilitate parasitism, but few studies have focused on this phenomenon in the field of plant-parasitic nematodes. In this study, we show that the plant-parasitic nematode Meloidogyne graminicola has evolved a novel effector, MgGPP, that is exclusively expressed within the nematode subventral esophageal gland cells and up-regulated in the early parasitic stage of M. graminicola. The effector MgGPP plays a role in nematode parasitism. Transgenic rice lines expressing MgGPP become significantly more susceptible to M. graminicola infection than wild-type control plants, and conversely, in planta, the silencing of MgGPP through RNAi technology substantially increases the resistance of rice to M. graminicola. Significantly, we show that MgGPP is secreted into host plants and targeted to the ER, where the N-glycosylation and C-terminal proteolysis of MgGPP occur. C-terminal proteolysis promotes MgGPP to leave the ER, after which it is transported to the nucleus. In addition, N-glycosylation of MgGPP is required for suppressing the host response. The research data provide an intriguing example of in planta glycosylation in concert with proteolysis of a pathogen effector, which depict a novel mechanism by which parasitic nematodes could subjugate plant immunity and promote parasitism and may present a promising target for developing new strategies against nematode infections.

Author summary

Post-translational modification (PTM) is a tool used by prokaryotic and eukaryotic cells to regulate protein activity, and many unique and important functions of proteins depend on appropriate PTMs. Evidence is emerging that plant pathogen effectors can utilize the host post-translational machinery to mediate their PTM and regulate their activity to facilitate parasitism. However, these biochemical modifications have been described only for a limited number of plant-parasitic nematode effectors. In this report, we identified the novel Meloidogyne graminicola effector MgGPP, which is important for nematode parasitism. We found that the effector MgGPP is secreted into host tissues and is subjected to glycosylation in concert with proteolysis in rice. Furthermore, we have shown that the proteolytical processing of MgGPP could change the subcellular trafficking of MgGPP, and the N-glycosylation of MgGPP can activate its function to suppress resistance gene (RBP-1/Gpa2)-mediated cell death, revealing a strategy of host-mediated PTM that is cleverly exploited by plant-parasitic nematodes to subjugate plant immunity and thereby promote parasitism.