真菌与齿小蠹的种间特异性共生及协同代谢机制

The symbiosis of different organisms increases the buffer ability of each individual to adapt to the environmental changes. Consequently, the symbiosis of fungi and bark beetles in forests often causes more serious damages during the process of the ongoing co-evolution. Although there is an extensive investigation of the stable symbiotic relationship between the bark beetles and fungi, the lack of exploiting mechanism behind hinders the understanding and utility of such relationship. In the post genomics era, the analysis on the composition and function of symbiotic micro flora for insect pests by metagenomics provides chances to reveal the symbiotic mechanism between bark beetles and fungi. The project takes the symbiosis between Ips beetles and fungi as model materials, which causes serious damage to the forests in the northern China, on the basis of different ecosystems linked host isolation and geographical isolation to the symbionts, to reveal the composition of diversities and functions for the symbiotic fungus communities in vitro using metagenomics, and to study whether the specific symbiosis between the two organisms exists, as well as subspecies or population coevolution. The combination of function analysis and verification experiment of the metagenome for mycobiota can reveal the effects that symbiotic fungi provides nutrition and complementary detoxification of host defensive compounds to bark beetles. The clarification of the symbiosis mechanism between Ips beetles and fungi could explain reasons for beetle population establishment and outbreak, in aid of providing new strategy for pest quarantine and control methods.

不同种类生物的共生增加了生物个体对环境变化的缓冲适应能力。森林生态系统内小蠹虫与真菌的共生，在不断发生的协同进化过程中，往往对森林造成更大的危害。尽管对小蠹虫与真菌之间能够建立稳定共生关系的认识十分广泛，但有关其机制缺乏深入揭示，阻碍了对这种共生关系的理解和利用。在后基因组学的时代，利用宏基因组学对植食性害虫共生微生物群落组成和功能的分析，为揭示小蠹虫与病原真菌的体外共生机制提供了条件。本项目将严重危害我国北方针叶林的齿小蠹属昆虫与真菌的共生关系作为研究对象，在共生体寄主隔离、地理隔离的背景下，利用宏基因组学揭示体外共生微真菌群落的多样性和生理功能特征，研究二者种间是否吻合特异性共生假说，包括种下的协同成种可能；宏基因组功能分析和验证实验相结合，揭示共生真菌对小蠹虫发育提供营养、协同小蠹虫解毒寄主防御性化合物的作用，从而阐明小蠹虫与真菌的共生机制，解释森林有害生物种群形成和成灾机制。

齿小蠹是针叶林木重要的蛀干害虫，该类昆虫与长喙壳类真菌存在共生关系。本研究对我国分布的所有10种齿小蠹的分布与危害等进行了详细调查，发现齿小蠹种下存在大量而显著的种下分化特征，显示寄主种类和地理隔离是这些分化的主要驱动因素。以传统的分离培养方法获得齿小蠹伴生可培养长喙壳真菌70余种，新种40余个。通过形态学特征和分子数据从亚洲落叶松八齿小蠹可培养共生真菌区系鉴定8个新种，分别为Ophiostoma genhense，O. hongxingense，O. lotiforme，O. multisynnematum，O. peniculi，O. pseudobicolor，O. subelongati和O. xinganense。明确并获得齿小蠹核心共生菌Ophiostoma bicolor不同地理种群。发现不同齿小蠹在不同地理区域与特定的长喙壳类真菌的特异性共生关系。通过落叶松八齿小蠹、华山松大小蠹等分离的长喙壳真菌进行致病性试验来评估致病性的强弱，确定了核心共生菌Ophiostoma bicolor致病性明显。除此之外，本研究以宏基因组学对光臀八齿小蠹和十二齿小蠹的伴生菌进行分析，发现6个与柠檬烯和松萜降解的基因，分别为K01825，K01782，K14731，K10533，K01692，K00128。这些基因分别对应的酶是2种羟烷基差向异构酶，1种内酯水解酶，1种柠檬烯氧化物水解酶，1种辅酶，1种乙醛脱氢酶。并发现了长喙壳类真菌的Sporothrix schenckii的K00412基因，该基因参与到ATP的合成。.本研究阐释出齿小蠹与其伴生长喙壳类真菌的特异性共生关系，通过筛选出共生菌的功能基因，为研究共生菌协同小蠹虫解毒寄主防御性化合物提供基础数据，也为进一步研究小蠹虫与昆虫的共生机制提供参考依据。