CDA基因在芒果炭疽病菌生长和致病过程中的作用

Anthracnose caused by Colletotrichum spp. is a very important postharvest disease of tropical fruits. A thorough understanding of the molecular mechanism involved in the pathogenesis of the fungi should help us to develop safer and more effective controlling strategies. Our preliminary results showed that three chitin deacetylase (CDA) genes were highly upregulated under the necrotrophic stage, suggesting these genes might be related to such pathogenesis events as ammonia production and secretion, host environmental pH regulation, pathogen cell wall modification and host defense reactions. In order to analyze the functions of the three CDA genes in the growth and pathogenesis of C.g, we are going to knock out them individually from the fungus genome to generate corresponding gene knockout mutants. The influences of CDA deletion on morphological and growth characteristics of the fungus will be characterized in relation to pathogenicity, and underlying mechanisms will also be studied at molecular level. The results obtained from this study should deepen our understanding of the pathogenesis of the fungi, and will most probably help us to identify target genes for future control of the disease, which will provide technical basis for developing safer and more effective control methods.

炭疽病是热带水果的主要采后病害，其安全有效地防治有赖于我们对该病原菌致病过程分子机制的充分了解。申请者业已发现芒果炭疽病菌Colletotrichum gloeosporioides (C.g）基因组中3个在侵染致病阶段高水平表达的几丁质脱乙酰酶（Chitin deacetylase，CDA）基因可能与C.g侵染过程中氨的分泌、寄主pH调控、细胞壁修饰、寄主的防御反应等致病性相关事件有密切关系。为阐明这3个CDA基因在该菌生长和致病过程中的具体作用，本项目拟通过外源基因重组技术从该菌基因组中分别敲除这3个CDA基因，研究CDA基因缺失突变对病原菌形态学特征、生长发育特性以及致病力的影响，并从分子水平上研究影响产生的机制。本研究结果可望加深人类对C.g致病机制的认识，有可能为今后利用分子手段控制热带水果炭疽病提供靶标基因，奠定安全有效防治该病的技术基础。

几丁质脱乙酰酶(Chitin deacetylase , CDA)催化植物病原真菌细胞壁几丁质分子脱去乙酰基生成壳聚糖，其在病原真菌生长和植物-病原真菌互作致病过程中发挥着重要的作用。由胶胞炭疽菌（Colletotrichum gloeosporioides，C.g）引起的炭疽病是造成水果采后损失的重要采后病害之一。目前仍缺乏关于CDA基因在C.g生长发育及侵染致病过程中的具体功能研究。本项目挖掘出C.g基因组中3个CDA基因，结构分析和功能预测显示编码的蛋白均有保守的CE4_SF/CICDA结构域，此结构域同NodB结构域同源，是催化真菌细胞壁几丁质转化为壳聚糖的功能结构。通过进一步检测3个CDA基因的表达水平，预测CDA基因可能与C.g生长发育、侵染致病及寄主的防御反应等致病性相关事件密切相关。.为阐明这3个CDA基因的具体作用，采用外源基因重组敲除策略分别获得3个CDA基因缺失突变体各3个株系。同野生型C.g对比，CDA基因缺失突变株可正常生长形成菌丝、产孢、形成附着孢。致病力检测显示，同野生型相比较，只有CDA3基因缺失突变株在芒果果实上的致病情况有明显稳定差异，表现为致病力显著下降。这主要是由于CDA3基因缺失后孢子萌发率和附着孢形成率显著降低。结果暗示CDA3基因在C.g的生长发育及侵染致病力中起主要功能。通过分别检测CDA1和CDA2基因缺失突变株中另外两个CDA基因的超量表达证明了C.g CDA基因具有功能冗余及互补性，因此单个CDA1和CDA2基因缺失后对生长发育和致病力无显著影响。本项目研究结果为明确CDA基因在炭疽病菌致病过程中的功能提供了理论依据，并为果实炭疽病的防治提供新的思路和借鉴。