Specific communication processes of distinct conidia types during germination, early colony development, and host plant infection of the fungal maize pathogen Colletotrichum graminicola

在过去的二十年里，关于丝状真菌引起的植物感染爆发的报道越来越多，包括玉米、小麦、水稻和马铃薯等重要作物。炭疽杆菌是玉米炭疽病的致病因子，仅在美国，每年就有10亿美元的经济潜力。在感染过程中，两种特定的感染性真菌孢子类型调节中心致病性过程。在被感染的叶片上形成的镰形分生孢子向周围的粘液分泌霉菌素衍生物。这些信号分子抑制这种孢子类型的萌发依赖于营养和孢子密度。另一方面，卵形分生孢子产生信号，使幼胚协调融合。有趣的是，这两种孢子特异性信号从根本上影响了这种玉米病原体的感染策略。由于这两种分泌信号在其他孢子类型中不存在，我们将寻求揭示禾本科孢的外部刺激、生物合成和这些孢子特异性信号的详细功能。霉孢素是次级代谢物，与氧化和渗透应激一样，参与保护紫外线辐射。在我们的前期实验中，我们发现蓝藻菌菌素生物合成的同源基因在C. graminicola中以组织依赖的方式表达。利用计算机分析，我们进一步确定了在这种真菌中产生霉孢素的一个假定的次级代谢物簇。在一种结合特异性菌素衍生物功能研究的方法中，我们将利用缺失突变体的RNAseq、遗传和表型分析，寻求确定谷草孢杆菌菌素的生物合成途径。基于这些发现，我们旨在揭示这些次生代谢物在该植物病原体孢子特异性生命周期和致病性中的作用。在丝状子囊菌中，营养细胞融合的形成是一个高度保守的过程。预计这一过程可以通过优化养分利用率和协调发育过程和生长模式来增加真菌菌落的适应性。在融合形成过程中，发生了未来融合伙伴的细胞对话：双方以交替的方式分泌一种未知的信号，引导相应的伙伴走向彼此。为了方便识别融合信号，我们建立了一个管道，包括信号产生，隔离和评估的方法。在此基础上，我们将采用比较卵形分生孢子和镰形分生孢子产生的分泌组的分析方法，通过HPLC/MS分析来识别相应的信号。此外，我们将使用缺失突变体的遗传和表型分析来验证所获得的结果。这将进一步确定融合信号作为谷草球菌可能的毒力因子的影响。

Within the last two decades, reports on outbreaks of plant infections caused by filamentous fungi increased, including important crop plants like corn, wheat, rice, and potato. Colletotrichum graminicola is the causal agent of corn anthracnose, a disease with the annual economic potential of about 1 billion US dollars only in the USA. During infection, two specific infectious fungal spore types regulate central pathogenicity processes. Falcate-shaped conidia formed on infected leaves secrete mycosporine derivatives into the surrounding mucilage. These signaling molecules inhibit the germination of this spore type in dependence of nutrients and spore density. Oval conidia, on the other hand, generate signals allowing the coordinated fusion of young germlings. Intriguingly, both spore-specific signals fundamentally influence the infection strategy of this maize pathogen. Since both secreted signals are absent from the other spore type, we will seek to unravel external stimuli, biosynthesis, and detailed functions of these spore-specific signals of C. graminicola. Mycosporines are secondary metabolites involved in protection from UV-radiation alike as oxidative and osmotic stress. In our pre-experiments we have found that homologous genes of the mycosporine biosynthesis in cyanobacteria are expressed in a tissue-dependent way in C. graminicola. Using in silico analyses, we were further able to identify a putative secondary metabolite cluster for the generation of mycosporines in this fungus. In an approach combining functional studies of specific mycosporine derivatives, we will seek to identify the biosynthesis pathways of mycosporines in C. graminicola applying RNAseq, genetic, and phenotypic analyses of deletion mutants. Based on these findings we aim to unravel the role of these secondary metabolites in spore-specific life-cycle and pathogenicity of this plant pathogen. Formation of vegetative cell fusions is a highly conserved process in filamentous ascomycetes. It is anticipated that this process increases the fitness of a fungal colony by optimizing nutrient availability and coordinating developmental processes and growth patterns. During the fusion formation, a cellular dialog of the future fusion partners takes place: both partners secrete a yet unknown signal in an alternate fashion, guiding the corresponding partners towards each other. To facilitate the identification of the fusion signal, we established a pipeline including methods for signal generation, isolation, and evaluation. Based on this pipeline we will apply analytical methods comparing the secretomes generated by oval and falcate conidia to identify the corresponding signal by HPLC/MS analyses. Further, we will verify the obtained results using genetic and phenotypical analyses of deletion mutants. This will additionally allow determining the impact of the fusion signal as a probable virulence factor of C. graminicola.