Pathogen-induced recruitment of a beneficial bacterium in wheat

<b>Plants are subjected to diverse stresses throughout their lives. Emerging theoretical framework suggests that they may have co-evolved multiple strategies to cooperate with microorganisms to cope with </b><b>stresses. However, empirical evidence underlying co-evolution processes and mutualistic plant-microbial interactions in stress scenarios are limited. In this study, we tested the hypothesis that infection by the soil-borne hemi-biotrophic pathogen <i>Fusarium pseudograminearum</i> (<i>Fp</i>), which causes a devastating crown rot disease on wheat, affects the community structure of the wheat-associated microbiome. Rhizosphere and plant samples were collected from a field experiment where durum wheat (<i>Triticum aestivum</i>) was naturally infected with <i>Fp </i>at different levels for individuals. Phylogenetic marker gene sequencing was used to profile microbial communities and evaluate effects of <i>Fp</i> infection on plant microbiomes. Our data revealed that diseased plants were associated with distinct rhizosphere and root endosphere microbiomes compared with healthy plants. We observed that infected plants had higher abundances of some taxa including a beneficial bacterium <i>Stenotrophomonas rhizophila</i> (SR80) in the rhizosphere soil and root endosphere. T</b><b>his bacterium </b><b>reached 3×10⁸ cfu g^-1 in the rhizosphere soil, accounting for up to 12% of the microbes in the root endosphere. Further analyses revealed that the abundance of SR80</b><b> had a positive linear correlation with the <i>Fp</i> load at base stems and expression of </b><b>defense</b><b> genes </b><b>in</b><b> leaves. </b><b>We were able to isolate SR80 from the rhizosphere, which upon re-introduction in soils promoted wheat growth, survival rates, and enhanced defense signaling in plant leaves, but only in the presence of the pathogen. This bacterium seems to have acted as an early warning system for plant defense against the <i>Fp</i>.</b><b> Together, these findings provide novel evidence for the potential protection of plants by a beneficial microbe against pathogens via modulation of the plant immune system.</b>

植物在整个生命周期中会经受多种胁迫。当前新兴的理论研究框架表明，植物可能已与微生物协同演化出多种协作策略，以共同应对各类胁迫。然而，目前针对胁迫环境下植物与微生物协同演化过程及互利互作关系的实证研究证据仍较为有限。本研究针对以下假说开展验证：引起小麦毁灭性冠腐病的土传半活体营养型病原菌假禾谷镰孢（*Fusarium pseudograminearum*，简称Fp）侵染，会改变小麦相关微生物组的群落结构。本研究从一项田间试验中采集根际土壤与植物样品，该试验中供试的普通小麦（*Triticum aestivum*）个体自然感染Fp的程度存在差异。通过系统发育标记基因测序技术解析微生物群落组成，并评估Fp侵染对植物微生物组的影响。测序结果显示，与健康植株相比，发病植株的根际土壤与根内微生物组群落结构存在显著差异。研究发现，染病植株的根际土壤与根内样本中，部分类群的相对丰度显著升高，其中包括有益细菌嗜根寡养单胞菌（*Stenotrophomonas rhizophila*，SR80）。该菌在根际土壤中的数量可达3×10^8 CFU·g^-1，在根内微生物组中占比最高可达12%。进一步分析表明，SR80的相对丰度与小麦基部茎秆的Fp载荷量及叶片防御基因的表达水平呈显著正线性相关。本研究成功从根际土壤中分离得到SR80，将其重新施入土壤后，仅在病原菌存在的条件下，即可促进小麦生长、提高植株存活率，并增强叶片中的防卫信号通路活性。该菌似乎可作为植物抵御Fp侵染的早期预警系统。综上，本研究结果为有益微生物通过调控植物免疫系统抵御病原菌侵染提供了全新的实证依据。