Abstract
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 gene Mg-PEL1 from M. graminicola. Quantitative real-time PCR assay showed that the highest transcriptional expression level of Mg-PEL1 occurred in pre-parasitic second-stage juveniles, and it was still detected during the early parasitic stage. Using in situ hybridization, we showed that Mg-PEL1 was expressed exclusively within the subventral esophageal gland cells of M. 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 targeting Mg-PEL1 showed an increased resistance to M. graminicola. In addition, using an Agrobacterium-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 of M. graminicola and 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.
Highlights
In nature, plants live in complex environments where they are continually exposed to various beneficial or harmful microbes (Rodriguez et al, 2019)
A NJ tree (Supplementary Figure 3) was constructed to examine the relationships among 37 pectate lyases. This phylogenetic tree shows that Mg-PEL1, Me-PEL1, Mj-PEL1, Mi-PEL1, and RsPEL3 are placed within a well-supported monophyletic clade; this clade is sister to the other clade comprising some pectate lyase sequences from bacteria and fungi, but far from other plant-parasitic nematodes (PPNs) pectate lyase sequences
The phylogenetic analysis revealed that Mg-PEL1 has a closer relationship to several pectate lyases from fungi and bacteria than to some pectate lyases from PPNs, which is in line with the general idea that PPNs got pectate lyases from fungi or bacteria through horizontal gene transfer (Vanholme et al, 2007)
Summary
Plants live in complex environments where they are continually exposed to various beneficial or harmful microbes (Rodriguez et al, 2019). The first line of immunity relies on the perception of pathogenassociated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), leading to PAMP-triggered immunity (PTI) (Jones and Dangl, 2006). Besides pathogen-derived PAMPs, the plant innate immune system can recognize some endogenous molecules of the host once the molecules are released into the extracellular environment during tissue disruption (Hou et al, 2019). These host-derived molecules are referred to as damage-associated molecular patterns (DAMPs), which are endogenous indicators of damage and can act as early and general activators of the plant immune system (Choi and Klessig, 2016; Quintana-rodriguez et al, 2018)
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