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Divergent Expression of Acidic and Alkaline Pectate Lyases in Ditylenchus destructor During Initial Infection Time
Bingxue Sun1, Bo Gao1, Yonghao Dong1
1National Collection of Plant-Associated Microbes (Hebei), IPM Innovation Center of Hebei Province, International Science and Technology Joint Research Center on IPM of Hebei Province, Plant Protection Institute, Hebei Academy of Agriculture and Forestry Sciences, Baoding 071000, China.
None:
Pectate lyase (PeL) is a key cell wall-degrading enzyme in the infection process of plant-parasitic nematodes, with a large gene family exhibiting functional redundancy. The dominant PeL isoform during the initial infection time course remains unclear. In this study, 21 Ddpel genes were identified in Ditylenchus destructor Thorne, 1945, 7 of which were differentially expressed during the initial infection time course of this nematode. The purified proteins of these seven DdPeLs showed pathogenicity toward both sweet potato and tobacco, and their optimal enzymatic pH varied significantly. Prior to host infection, D. destructor preferentially expresses Ddpel genes encoding pectate lyase with higher activity at pH 5.8. However, within 5 days post-inoculation with nematodes, the expression of genes encoding acidic DdPeL enzymes (enzymes with optimal activity in acidic pH) was upregulated, while genes encoding alkaline DdPeL enzymes (optimal activity in alkaline pH) were concurrently downregulated. Through site-directed mutagenesis, we demonstrated that the loss of enzymatic activity in DdPeLs abolished their ability to induce plant cell death. Furthermore, when acidic or alkaline DdPeLs were pre-treated with dialysis in their respective optimal pH buffers prior to infiltration, their pathogenicity was significantly enhanced. Together, these findings demonstrate that enzymatic activity, governed by protein structure and local pH, is a key determinant of pathogenicity. Previous studies have reported that phytopathogens can secrete organic acids during the initial infection phase, leading to localized acidification of the host microenvironment. We therefore hypothesize that, during the initial infection time course, nematodes may actively acidify the host microenvironment to specifically enhance the enzymatic activity of acidic DdPeLs, thereby promoting cell wall degradation and facilitating infection establishment.
