蜕皮激素在昆虫抵御真菌侵染中的功能及以此为靶标的昆虫病原真菌改良

昆虫病原真菌已被广泛用于害虫生物防治。但在侵染昆虫过程中，真菌面临宿主各个层面的抵御，二者相互作用的结果直接影响了菌株的杀虫效果。课题组前期研究发现，球孢白僵菌侵染大蜡螟导致蜕皮激素20E显著上调，免疫反应激活；但在菌株中表达20E失活蛋白(病毒LdMNPV的EGT基因)，则降低了昆虫20E浓度，免疫反应受到抑制。据此推测20E是昆虫应对真菌侵染的一个重要信号分子，可成为菌株遗传改良的新靶点。为验证该假设，本研究拟分析不同昆虫病原真菌侵染宿主后的20E浓度变化，弄清20E上调是否为一个共性现象及相应的分子机制；进一步筛选不同20E失活蛋白进行菌株遗传改良，分析在真菌侵染过程中降低20E水平对宿主免疫反应、生长发育、行为、体内细菌等的影响，评价上述改变对菌株杀虫效果的影响。研究的开展将阐明昆虫蜕皮激素在真菌与宿主互作中的作用，为菌株遗传改良提供新靶点，促进真菌杀虫剂的应用。

Entomopathogenic fungi have been used as environment-friendly insecticides for pest control. However, insect can resist fungal infection with various defense mechanisms and the interaction between fungi and insect will affect fungal insecticidal effects. Our previous study showed infection by Beauveria bassiana on Galleria mellonella larvae can cause the increase of 20-OH-ecdysone (20E) titer which upregulates host defense reactions, including activation of PO cascade and expression of antimicrobial genes. A 20E inactivation gene EGT, encoding the ecdysteroid UDP-glucosyltransferase of Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV), was expressed in B. bassiana. EGT transgenic strains decreased 20E titer and immune reactions during pathogenesis. We deduced 20E is an important signal molecular for insect defense reactions against fungal infection and can become a potential target for fungal genetic engineering. To prove this hypothesis, this study will analyze the change of 20E titer in various insects which are infected by different pathogenic fungi respectively. To obtain fungal strains (B. bassiana) with high virulence, we will screen various 20E inactive genes and analyze the effects of transgenic strains on immune reactions, development, behavior, and bacteria of host. Effects of these changes on fungal virulence will be evaluated. These studies will help us to understand the functions of 20E in the interaction between insect and fungi and provide an effective target for fungal genetic engineering. This study will also accelerate the development of fungal insecticides.