A Meloidogyne graminicola Pectate Lyase Is Involved in Virulence and Activation of Host Defense Responses

Plant-parasitic nematodes secrete an array of cell-wall-degrading enzymes to overcome the physical barrier formed by the plant cell wall. Here, we describe a novel pectate lyase geneMg-PEL1fromM. graminicola. Quantitative real-time PCR assay showed that the highest transcriptional expression level ofMg-PEL1occurred in pre-parasitic second-stage juveniles, and it was still detected during the early parasitic stage. Usingin situhybridization, we showed that Mg-PEL1 was expressed exclusively within the subventral esophageal gland cells ofM. graminicola.The yeast signal sequence trap system revealed that it possessed an N-terminal signal peptide with secretion function. Recombinant Mg-PEL1 exhibited hydrolytic activity toward polygalacturonic acid. Rice plants expressing RNA interference vectors targetingMg-PEL1showed an increased resistance toM. graminicola. In addition, using anAgrobacterium-mediated transient expression system and plant immune response assays, we demonstrated that the cell wall localization of Mg-PEL1 was required for the activation of plant defense responses, including programmed plant cell death, reactive oxygen species (ROS) accumulation and expression of defense-related genes. Taken together, our results indicated that Mg-PEL1 could enhance the pathogenicity ofM. graminicolaand induce plant immune responses during nematode invasion into plants or migration in plants. This provides a new insight into the function of pectate lyases in plants-nematodes interaction.