Scab,由生物营养真菌病原体Venturiainaequalis引起,是苹果经济上最重要的疾病。在感染期间,V.Inaequalis定植于表皮下宿主环境,在那里它会发展出专门的感染结构,称为跑步者菌丝和基质。这些结构被认为与营养获取和效应因子(毒力因子)递送有关,但也会产生促进感染周期的分生孢子。尽管它们很重要,很少有人知道这些结构是如何区分的。同样,关于这些结构如何被保护免受宿主防御或宿主免疫系统的识别,目前还不知道。为了更好地理解这些过程,我们首先对培养中发育的叶枯草孢子形成的管状菌丝进行了糖苷连锁分析。这项分析表明,叶枯草细胞壁主要由葡聚糖(44%)和甘露聚糖(37%)组成,而几丁质的比例要小得多(4%)。接下来,我们使用转录组学和共聚焦激光扫描显微镜来提供对跑步者菌丝和基质细胞壁碳水化合物组成的见解。这些分析表明,在表皮下宿主定植期间,推测与免疫原性碳水化合物的生物合成相关的叶枯草的基因,如几丁质和β-1,6-葡聚糖,相对于培养物的生长被下调,而在跑步者菌丝和基质的表面,几丁质脱乙酰化为免疫原性较低的碳水化合物壳聚糖。这些变化有望使跑者菌丝和基质的表皮下分化。以及保护这些结构免受宿主防御和宿主免疫系统的识别。重要性植物病原真菌是对粮食安全的主要威胁。其中包括表皮下病原体,通常会导致潜伏的无症状感染,使他们难以控制。这些病原体的一个关键特征是它们能够区分特殊的表皮下感染结构,到目前为止,在很大程度上仍然被研究不足。这是典型的Venturiainaequalis,导致结痂,苹果经济上最重要的疾病。在这项研究中,我们证明,在表皮下宿主定植期间,V.inaequalis下调与两种免疫原性细胞壁碳水化合物的生物合成相关的基因,几丁质和β-1,6-葡聚糖,并用免疫原性较低的碳水化合物覆盖其表皮下感染结构,壳聚糖。预计这些变化将使V.inaequalis的宿主定植成为可能,并为理解其他植物病原真菌的表皮下宿主定植奠定了基础。这样的理解很重要,因为它可能会为针对表皮下植物病原真菌的新型控制策略的开发提供信息。
Scab, caused by the biotrophic fungal pathogen Venturia inaequalis, is the most economically important disease of apples. During infection, V. inaequalis colonizes the subcuticular host environment, where it develops specialized infection structures called runner hyphae and stromata. These structures are thought to be involved in nutrient acquisition and effector (virulence factor) delivery, but also give rise to conidia that further the infection cycle. Despite their importance, very little is known about how these structures are differentiated. Likewise, nothing is known about how these structures are protected from host defenses or recognition by the host immune system. To better understand these processes, we first performed a glycosidic linkage analysis of sporulating tubular hyphae from V. inaequalis developed in culture. This analysis revealed that the V. inaequalis cell wall is mostly composed of glucans (44%) and mannans (37%), whereas chitin represents a much smaller proportion (4%). Next, we used transcriptomics and confocal laser scanning microscopy to provide insights into the cell wall carbohydrate composition of runner hyphae and stromata. These analyses revealed that, during subcuticular host colonization, genes of V. inaequalis putatively associated with the biosynthesis of immunogenic carbohydrates, such as chitin and β-1,6-glucan, are downregulated relative to growth in culture, while on the surface of runner hyphae and stromata, chitin is deacetylated to the less-immunogenic carbohydrate chitosan. These changes are anticipated to enable the subcuticular differentiation of runner hyphae and stromata by V. inaequalis, as well as to protect these structures from host defenses and recognition by the host immune system. IMPORTANCE Plant-pathogenic fungi are a major threat to food security. Among these are subcuticular pathogens, which often cause latent asymptomatic infections, making them difficult to control. A key feature of these pathogens is their ability to differentiate specialized subcuticular infection structures that, to date, remain largely understudied. This is typified by Venturia inaequalis, which causes scab, the most economically important disease of apples. In this study, we show that, during subcuticular host colonization, V. inaequalis downregulates genes associated with the biosynthesis of two immunogenic cell wall carbohydrates, chitin and β-1,6-glucan, and coats its subcuticular infection structures with a less-immunogenic carbohydrate, chitosan. These changes are anticipated to enable host colonization by V. inaequalis and provide a foundation for understanding subcuticular host colonization by other plant-pathogenic fungi. Such an understanding is important, as it may inform the development of novel control strategies against subcuticular plant-pathogenic fungi.