菌丝内生细菌及其宿主真菌共生体系研究进展

微生物共生普遍存在于自然界中,真菌-细菌联合体能以多种方式相互作用,共同发挥各种生态功能。有些细菌驻留在真菌菌丝内部,借以调控真菌的生长、发育、分布和次级代谢过程,这些细菌被称为菌丝内生细菌（endohyphal bacteria, EHB）。EHB的研究揭开了微生物生态学的一个新篇章,是真菌与细菌共生关系中最紧密的代表。在逆境条件下,EHB可以调节寄主生殖机制相关的关键成分或步骤,诱导植物激素类物质的产生,对寄主真菌具有辅助性保护作用。研究最深入的真菌-EHB共生体系是植物致病性根霉菌Rhizopus sp.与伯克霍尔德氏菌Burkholderia sp.,引起水稻幼苗枯萎病所必需的植物毒素——根霉素是由伯克霍尔德氏菌所产生的,而非寄主根霉菌本身产生的。EHB也会影响定殖于高等植物的内生真菌的生态和多样性。在某些情况下,EHB还有助于激活参与识别、转录调节和初级代谢蛋白合成过程的相关基因。目前已开发出了无菌培养分离EHB的方法,然而对真菌-EHB共生体系的研究尚不够深入。综述了菌丝内生细菌EHB及其与宿主真菌的共生体系,阐述这些伴侣之间复杂微妙的相互关系,以及EHB对宿主真菌和宿主植物生长和发育的影响,并对该领域的研究方向提出了建议。

Research progress on endohyphal bacteria and their symbiosis with host fungi

Microbial symbioses are ubiquitous in nature wherein fungal bacterial complexes can interact in diverse ways and collectively perform various ecological functions. Some bacteria reside within the hyphae of fungi and regulate the growth, development, distribution, and secondary metabolism of the fungi; these bacteria are referred to as endohyphal bacteria (EHB). Recent studies on EHB have revealed a novel chapter in microbial ecology that represents the most intimate interaction among fungi and bacteria symbioses. EHB have been found to regulate key components of host reproductive machinery, induce the production of phytohormones, and play a complementary protective role for fungi under stress conditions. The most well-studied fungi-EHB symbiotic system is the phytopathogenic fungus Rhizopus sp. and its EHB Burkholderia sp., the phytotoxin essential for causing rice seedling blight is produced by the endosymbiont rather than the host fungus. EHB were found to affect the ecology and diversity of endophytic fungi that colonize higher plants. In some cases, EHB help in activation of genes involved in the recognition processes, transcription regulation, and primary metabolic protein synthesis. Although methods have been developed to isolate EHB in axenic culture, many fungi-EHB symbiotic systems still remain unexplored. This review article focuses on EHB and endohyphal symbioses with host fungi, the complex and delicate relationships among these partners, and the effects of EHB on the growth and development of host fungi and plants and proposes future research directions in this field.