鸡枞菌转录组分析揭示其对木质纤维素的降解功能

摘要

[Objective] To study whether Termitomyces albuminosus can degrade lignocelluloses and to understand the symbiotic relationship between termite mushroom and fungus-growing termite.[ Methods] cDNA library of T.albuminosus was sequenced by the Roche 454 GS FLX Titanium platform,and the diverse enzymes relevant to degradation of cellulose and lignin of symbiotic fungus T. albuminosus were analyzed. [ Results ] Eighth sequencing run resulted in a total of 82386 reads (express sequence tags,EST).After removing the vector and primer sequences,the remained 54410 reads were assembled into 3301 contigs and 3193 singletons. Comparing sequence similarity with known proteins,these sequences,representing approximately 2681 unique genes,were successfully annotated using BLAST searches (E-value ≤ 1e-10) against the Nr,SwissProt and CDD databases.The T.albuminosus transcripts included 33 enzymes putatively involved in cellulose and hemicelluloses biodegradation.5 enzymes could hydrolyze cellulose and others had catalytic activities for degradation of hemicelluloses,starch and glycogen and chitin.Moreover,four genes encoding laccases and a single aryl-alcohol oxidase which could degrade lignin were also identified.These results revealed symbiosis fungus T.albuminosus had many laccases and possibly decomposed phenolic compounds from plant litter. [ Conclusions ] Data presented in this study indicated that T.albuminosus had the ability to degrade lignin,which made cellulose more easily degraded by the cellulase produced by fungus-growing termite.%[目的]探究鸡枞菌是否能降解木质纤维素成分,并理解其与共生白蚁之间的共生关系.[方法]本研究是应用新一代高通量测序技术454 GS FLX Titanium对鸡枞菌的转录组进行测序,挖掘鸡枞菌中能参与降解纤维素和木质素等成分的多样性酶系.[结果]八分之一的RUN测序总共得到了82386条表达序列标签,去除引物和载体等序列后,剩余的54410条序列被拼接成3301条contigs以及3193条singletons.根据序列相似性,将这些unigenes与三大蛋白数据库(Nr数据库、SwissProt数据库、CDD数据库)中的蛋白序列进行BLAST比较,发现有2681条基因与其他生物的已知基因有不同程度的相似性.在鸡枞菌的这些转录产物中,有33条编码可能参与降解纤维素或半纤维素的酶基因,其中包括5种纤维素酶以及28种水解半纤维素、淀粉或几丁质等物质的酶类.更重要的是,还发现了4种漆酶以及一种芳基乙醇氧化酶基因,这些都是能有效降解木质素的酶类.这些结果揭示了鸡枞菌中存在漆酶并可能有效降解植物残渣中的酚化合物.[结论]这些基因的发现说明了鸡枞菌能降解木质素,并能与共生白蚁分泌的纤维素酶协同作用有效降解纤维素.