The Lasiodiplodia theobromae genome encodes numerous glycoside hydrolases involved in organic matter degradation and conducive to pathogen infection, whereas their molecular mechanisms are still largely unknown. Here, we identified the glycoside hydrolase family 28 endopolygalacturonase LtEPG1 in L. theobromae and characterized its function in detail. LtEPG1 acts as a virulence factor during L. theobromae infection. Overexpression and silencing of LtEPG1 in L. theobromae led to significantly increased and decreased lesion areas, respectively. Further, the high transcript level of LtEPG1 during the infection process supported its virulence function. Polygalacturonase activity of LtEPG1 was substantiated by detecting its ability to degrade pectin. Furthermore, LtEPG1 functioned as microbe-associated molecular patterns during the infection process. Both transient expression of LtEPG1 in planta and infiltration of purified LtEPG1 triggered cell death in Nicotiana benthamiana. Site-directed mutation of LtEPG1 indicated that the enzymatic activity of LtEPG1 is independent from its elicitor activity. A protein kinase, KINβ1, was shown to interact in the yeast two‐hybrid system with LtEPG1. This interaction was further confirmed in vitro using a pull-down assay. Our data indicate that LtEPG1 functions as a polygalacturonase and also serves as an elicitor with two independent mechanisms. Moreover, LtEPG1 may be able to manipulate host immune responses by regulating the KINβ1-mediated signal pathway and consequently promote its own successful infection and symptom development.

该Lasiodiplodia theobromae基因组编码大量的糖苷水解酶参与了降解有机物，有利于病原体感染，而其分子机制仍知之甚少。在这里，我们确定了L. theobromae中的糖苷水解酶家族28内聚半乳糖醛酸酶LtEPG1，并详细描述了其功能。LtEPG1在Theobromae感染过程中充当毒力因子。过表达和沉默LtEPG1在L. theobromae导致显著增加，分别减少病变区。此外，LtEPG1的高转录水平在感染过程中支持其毒力功能。LtEPG1的聚半乳糖醛酸酶活性通过检测其降解果胶的能力得到证实。此外，LtEPG1在感染过程中起微生物相关分子的作用。LtEPG1在植物中的瞬时表达和纯化LtEPG1的浸润均引起烟草死亡。LtEPG1的定点突变指出LtEPG1的酶活性独立于其激发子活性。已证明蛋白激酶KINβ1在酵母双杂交系统中与LtEPG1相互作用。使用下拉测定法在体外进一步证实了这种相互作用。我们的数据表明LtEPG1充当聚半乳糖醛酸酶，并且还具有两个独立机制的激发子。此外，LtEPG1可能能够通过调节KINβ1介导的信号通路来操纵宿主的免疫反应，从而促进其自身成功的感染和症状发展。