模拟微重力效应下小麦幼苗内生微生物组对宿主抗性调控机制研究

The resistance of plants with an important life-support function for manned space flight to phytopathogens was decreased under space microgravity. Our preliminary study showed that under microgravity simulation, the sensitivity of wheat seedlings to root rot was increased, moreover, the abundances of the wheat endophytic bacteria closely related to host resistance decreased. These results suggested that the gravity change may mediate changes in host resistance through endophytic microbial flora. However, the relationship between changes of endophytic microorganisms and host resistance under the change of gravitational force remains unclear, and no studies have been reported on the construction of appropriate artificial microbiome to regulate host resistance under microgravity. Therefore, the objective of this project is to clarify the regulation mechanism of the endogenous microbiome in wheat seedlings on host's resistance under microgravity stimulation. We plan to conduct this study from three aspects: (1) analyzing the response of endophytic microorganisms of wheat seedlings to the changes of gravitational force using high-throughput sequencing and bioinformatics; (2) studying the relevance and causality between changes of endogenous microbime and the changes of resistance in wheat under the influence of gravitation by the multivariate statistical analysis of the changes of the defensive enzymes, defensive hormones and resistance genes of wheat seedlings, the isolation of the endophytic strains and the inoculation to plants for verification; (3) establishing an artificial microbial flora to maintain host’s high resistance under microgravity through composite test, random walk, machine monitoring study and plant experimental verification. This study will not only give a new insight into clarifying the role of gravity in the process of plant-microorganism co-evolution, but also provide a theoretical basis for enhancing plant resistance under microgravity by artificial bacterial colonization.

载人航天中发挥着重要生命保障功能的植物，在微重力下对病菌的抗性减弱。内生微生物组具有增强植物抗性的作用。申请人前期发现模拟微重力下小麦对根腐病菌的敏感性增加，其内生菌中与抗病相关的菌属丰度下降。这提示重力改变可通过内生微生物介导宿主的抗性变化。然而，重力改变下植物内生微生物组是如何改变进而调控宿主抗性的机制尚不清楚。本项目首先利用高通量测序、生物信息学分析小麦幼苗的内生微生物组对模拟微重力的应答；其次，结合重力改变下小麦防御酶活、防御激素、抗性基因表达等抗性指标的相应变化，采用多元统计、菌株分离培养、接种验证研究重力改变下内生菌群变化与小麦抗性变化间相关/因果性；最后通过组合实验、机器学习、接种验证分析抗性相关菌株之间的协同交互关系，构建微重力下调节植物高抗性的人工菌群。研究结果将为阐明重力在植物-内生微生物组共同进化中的作用、通过移植人工菌群增强微重力下植物的抗性提供一定的理论基础。

小麦（Triticum aestivum L.）是生物再生生命保障系统的主要粮食作物之一，可以在长期的太空任务中为人类提供氧气和水，并提供心理安慰。然而，在太空微重力环境下生长的小麦抗性差，容易受到病原菌的侵染，且生长速度相对较慢。植物内生微生物组为宿主提供了额外的基因编码功能，在宿主营养、抗病和抵御非生物胁迫中具有重要作用。因此，探究重力改变下植物内生微生物组是如何改变进而调控宿主生长和抗性的机制可能是解决当前微重力环境下植物栽培相关挑战的关键。在本项目中，我们首先研究了重力改变效应下小麦幼苗内生微生物组的结构与功能变化，发现模拟微重力效应显著降低了根内生细菌的多样性，影响根内生细菌群落的组成和功能，模拟微重力效应促使植物改变了内生细菌微生物的富集策略以应对重力胁迫；我们进一步研究了重力改变下内生菌群变化与小麦抗性变化的相关性，发现了肠杆菌属、芽孢杆菌属、短芽孢杆菌属、鞘脂单胞菌属、甲基杆菌属可能是模拟微重力效应下通过影响氧化酶活、茉莉酸、水杨酸、吲哚乙酸和L-色氨酸含量影响植物生长和抗性的潜在菌属；最后分离筛选了纯菌株并成功构建了由鞘脂菌属Sphingobium-sp.3、甲基杆菌Methylibium-sp.Sup10、副球菌属Paracoccus-sp.13、短芽孢杆菌Brevibacillus-sp.37四种特定菌株构成的人工菌群，其能够增加模拟微重力效应下小麦的株高、防御激素和酶活的含量。此外，研究表明模拟微重力效应对根际微生物的群落组成和结构并没有显著的影响。这些研究结果能够为阐明地球重力在植物-内生微生物共生体共同进化中的作用提供理论依据，也为后继通过核心功能菌群人工重组、精准移植增强微重力下植物抗病抗逆效果、建立载人航天生命保障的植物高效栽培系统奠定技术基础。