支原体类内生细菌对宿主丛枝菌根真菌的生物学特性和抗病害胁迫的影响研究

Arbuscular Mycorrhizal Fungi (AMF) are symbionts of most terrestrial plants, and play the important roles on plant growth promoting, tolerance against various stresses and resistance to disease for plant hosts. Pepper has global economic importance. Phytophthora blight of pepper caused by Phytophthora capsici is the destructive fungal disease, which is soilborne and difficult to control. This disease has become a serious obstacle to sustainable development of the pepper industry. In recent years, some AMF taxa were found that they harbored obligate mycoplasma-related endobacteria (MRE) in the cytoplasm of their hyphae and spores, but the others did not harbor any MRE. Different AMF taxa do not have consistent effects of the benefits on plant hosts, and one possible source of this variability is MRE. In this project, we will use AMF taxa and their MRE as the interaction model. The isogenic lines of AMF with curing and infection of MRE will be established, combined with transcriptome sequencing technology. The effects of these MRE on the biology of their AMF hosts also will be understood. Meanwhile, the symbiosis between AMF and pepper plants will be established, and following this experimental system, the influences of MRE on the disease resistence of their AMF hosts against pepper Phytophthora blight will be elucidated. The goals of this study are to understand the roles and effects of MRE on the benefits of plant growth promoting and resistance to various stresses and disease for plant hosts from the symbiont between AMF and plants, and explain the underlying sources of variability of the benefits from the symbiont between the different AMF taxa and plant hosts potentially caused by MRE. The results will effectively contribute to development and utilization for the resources of AMF.

丛枝菌根真菌(AMF)能与绝大多数陆生植物形成互惠共生体,在宿主植物生长发育和抗病抗逆性等方面发挥了重要作用。辣椒是全球性重要经济作物。辣椒疫病是辣椒疫霉引起的毁灭性土传病害，已成为制约辣椒产业可持续发展的严重障碍。近年来，在许多AMF中发现专性共生内生细菌(MRE)，不同AMF种类对宿主植物的影响和作用差异明显，MRE可能是影响AMF与植物共生体抗逆性和抗病性等特性的重要因素。本项目将以AMF与MRE为互作模型，利用MRE与宿主AMF的治愈技术、MRE侵染无MRE的AMF技术，结合转录组测序技术，阐明MRE对宿主AMF的生物学特性的影响；同时构建AMF与辣椒的共生体系，阐明MRE在AMF对宿主疫病抗病害胁迫中的作用和影响。本研究将有助于进一步理解MRE如何参与AMF与宿主植物的互惠共生，明确MRE在AMF对宿主生长发育和抗病性中的影响和作用。研究结果将为AMF资源开发利用奠定重要基础。

丛枝菌根真菌广泛分布，能与植物根系形成互惠共生体。研究发现不同AMF与宿主植物互作有明显差异，同时许多AMF种类存在专性内生细菌 (MRE)，在促进植物生长发育，提高植物抗逆性，降低病害胁迫影响等方面具有重要作用。本研究选择有MRE的明根孢囊霉 (Rc)、摩西斗管球囊霉 (Fm)和幼套球囊霉 (Ce) 以及无MRE根内根孢囊霉 (Ri) 为研究材料，通过与辣椒植株建立共生体系，分别测定辣椒菌根侵染率和促生作用，以及叶绿素含量、菌根定殖率、几丁质酶和苯丙氨酸解氨酶 (PAL) 等生理指标，评价疫病防治效果，以探究MRE在AMF对辣椒植株的生长作用及对辣椒疫病生防的潜在作用和影响。 (1) 在盆栽条件下，不同AMF对宿主植物促生作用存在显著差异。接种MRE共生Rc、Fm和Ce辣椒植株叶片叶绿素含量有显著性差异，分别增加了48.8%、46.1%和39.53%，而无MRE共生Ri在叶绿素含量上无显著差异。(2)不同的AMF侵染宿主辣椒植物的方式存在差异，四种AMF均能在辣椒根组织中定殖，产生菌丝、泡囊和丛枝结构，无MRE的Ri由孢子萌发后附着在根表皮外面形成附着胞，通过附着孢侵入点侵入根表皮，而MRE的Fm、Rc和Ce由孢子萌发菌丝后通过侵入点直接侵入根表皮细胞。同时， Fm的侵染定殖率为85.8%，显著高于无MRE的Ri，而Rc和Ce为66.65%和62.84%，与Ri 定殖率 (66.65%)无显著差异。(3) 通过形态学结合基于LSU-28S的分子系统发育树鉴定，四种AMF为明根孢囊霉、摩西斗管球囊霉、幼套球囊霉和根内根孢囊霉。通过SSU-16S分子检测，Ri无MRE，而Fm、Rc和Ce均有MRE。(4)在盆栽条件下，将四种AMF-辣椒植株-辣椒疫霉(Pc)互作， MRE的Fm（22.7%）、Rc （33.6%）和 Ce 防（22.7%）防效低于无MRE的Ri（48.5%）。有MRE的3种AMF (Fm、Rc和Ce)接种Pc后几丁质酶活性与PAL活性显著高于无MRE的Ri，四种AMF均促进了宿主植物增加上述2种酶活性以降低病害胁迫。本研究表明，MRE在AMF对宿主促生和抗病害作用等生态功能中具有潜在作用和影响，为揭示MRE在AMF与宿主植物的互惠共生体中的作用奠定重要基础，为 AMF 在农业生产实践中的应用提供理论依据，帮助人们对AMF作用和应用价值更深入的理解。