水生壶菌与其宿主雨生血球藻的相互作用研究

The zoosporic chytridiomycota (chytrid) are the most primitive fungal lineages. Many chytrid species can specifically parasitize other organisms, including algae, animal and other fungi, representing important components in aquatic ecological systems. However, the mechanisms underlying species-specific parasitism of chytrid remain largely unknown. We will utilize the unicellular green alga Haematococcus pluvialis and its parasite chytrid Paraphysoderma sedebokerensis as a model system to investigate the interaction between the host and pathogen. Previous studies indicated that P. sedebokerensis constitutively expressed a large number of carbohydrate-active enzymes（CAZymes）involved in cell wall degradation, of which many genes were up-regulated during the penetration and germination of the chytrid on the host algal cell walls. Based on these observations, we hypothesized that the oligosaccharides released from H. pluvialis cells walls under the biotic stress may function as signals, which can in turn up-regulate biosynthesis of pathogenic effectors and cell wall-degrading enzymes. We will employ the approaches of transcriptomics, bioinformatics and biochemistry to identify the genes encoding the effectors and CAZymes involved in host cell wall penetration, and to dissect the host cell damage-associated oligosaccharides that may stimulate the expression of these genes. This project will not only provide insights into the interaction between H. pluvialis and P. sedebokerensis but also will help to understand the ecological significance of chytrids.

壶菌被认为是起源最早的真菌，它们专一性侵染藻类、动物和其他真菌，是水生生态系统的重要组成，然而关于壶菌是如何专一性侵染宿主细胞的机制尚不明确。本项目将以一种单细胞绿藻——雨生血球藻与其特异性病原壶菌（Paraphysoderma sedebokerensis）作为模式系统，来研究壶菌与血球藻的互作机制。前期工作结果表明，在壶菌着生于宿主细胞壁的过程中，壶菌表达大量的多糖降解酶类作用于宿主藻细胞壁，因此我们推测，在生物胁迫下藻细胞壁因损伤产生的寡糖类次生代谢物可能对壶菌分泌促进侵染的效应蛋白或多糖水解酶起到正向调控的作用。本项目拟通过转录组学、生物信息学及生物化学的方法鉴定壶菌作用于藻细胞壁的效应蛋白和多糖水解酶、解析宿主细胞壁来源的寡糖类信号分子，在此基础上阐释壶菌专一性侵染血球藻细胞的生物学机制。本项目的实施也将为壶菌-藻细胞互作研究以及评估壶菌在生态系统中的功能提供基础。

壶菌是如何专一性侵染宿主细胞的机制尚不明确。本研究以雨生血球藻（Haematococcus pluvialis）与其特异性病原真菌（Paraphysoderma sedebokerensis）作为模式系统研究二者的互作机制。本研究通过转录组学、生物信息学及生物化学的方法揭示了真菌-血球藻互作过程中早期的响应基因，鉴定了真菌作用于藻细胞壁的多糖水解酶，证实了宿主细胞壁来源的寡糖类信号分子对真菌的毒力相关基因的调控，在此基础上阐释了真菌专一性侵染血球藻细胞的生物学机制。结果表明，在真菌着生于宿主细胞壁的过程中，真菌表达大量的多糖降解酶类如glucannase和mannanase作用于宿主藻细胞壁多糖，藻细胞壁因损伤产生的寡糖类次生代谢物manno-oligosaccharides对促进真菌侵染的多糖水解酶等毒力基因表达起到正向调控的作用。本研究将为真菌-藻细胞互作以及评估壶菌在生态系统中的功能提供基础。.主要结果和结论如下：.1、P. sedebokerense CMBB利用glucan，mannose和glucose作为碳源，利用L-Cysteine，Alanine，Arginine，Asparagine和Glutamine等作为氮源；.2、P. sedebokerensis CMBB显著表达的基因编码CAZymes，Serine-type endopeptidases，Oxidoreductase和Chloride-channel proteins，可能为真菌寄生所必需的基因；血球藻早期防卫反应相关基因编码Kinase，Integral component of membrane，ABC transporter and ATPase，Stress response和Oxidoreductase等；.3、lysozyme，beta-1,4-glucanase和beta-1,4-mannanase，以及氨基酸代谢和甲硫氨酸合成在真菌侵染过程中起着重要作用，通过抑制剂可以阻断真菌感染血球藻的进程；.4、血球藻细胞壁水解产物manno-oligosaccharides诱导真菌毒力基因的表达，说明宿主细胞壁通过损伤相关的分子模式促进真菌寄生的正反馈调节作用。