<i>Blumeria hordei</i> affects volatile emission of susceptible and resistant barley plants and modifies the defense response of recipient plants

The barley powdery mildew disease caused by the biotrophic fungus <i>Blumeria hordei</i> (<i>Bh</i>) poses enormous risks in crop production due to yield and quality losses. Plants and fungi can produce and release volatile organic compounds (VOCs) that serve as signals in plant communication and defense response. The present study aims to identify VOCs released by barley (<i>Hordeum vulgare</i>) during <i>Bh</i>-infection and to decipher VOC-induced disease resistance in receiver plants. VOC profiles of susceptible <i>MLO</i> wild type (<i>MLO</i> WT) and a resistant near-isogenic backcross line (<i>mlo5</i>) were characterized over time (1 day or three days after <i>Bh</i> inoculation) using TD-GC/MS. Comparative analysis revealed genotype-dependent VOC profiles and significant differences in emission rates for <i>β</i>-caryophyllene, linalool, (<i>Z</i>)-3-hexenol, and methyl salicylate. Furthermore, susceptible barley plants were exposed to the complex VOC bouquet of <i>MLO</i> WT or <i>mlo5</i> sender plants in plant-to-plant communication. We found that VOC-induced resistance in receiver plants depended on the sender genotype in a <i>Bh</i> susceptibility assay. Additionally, untargeted metabolomics and gene expression studies provide evidence toward an SA-dependent pathway mediating VOC-induced resistance against powdery mildew. Exogenous application of methyl salicylate resulted in enhanced expression of the <i>BARLEY CHEMICALLY INDUCED-4</i> marker gene and induced resistance in receiver plants. The findings suggest genotype-dependent alterations in barley VOC profiles during a biotrophic plant-fungus interaction and show a VOC-mediated resistance that shares components with salicylic acid-related pathways. The VOC signals identified here could serve as non-invasive markers for disease progression in barley-powdery mildew interactions and as signals for resistance induction in recipient plants.由活体营养型真菌布氏白粉菌（*Blumeria hordei*，简称Bh）引起的大麦白粉病，会造成作物产量与品质损失，对农业生产构成巨大威胁。植物与真菌均可产生并释放挥发性有机化合物（volatile organic compounds, VOCs），这些VOCs可作为植物通讯与防御反应的信号分子。本研究旨在鉴定大麦（*Hordeum vulgare*）受Bh侵染后释放的VOCs，并解析受体植物中VOC诱导的抗病性。研究人员采用热脱附-气相色谱-质谱联用技术（TD-GC/MS），在接种Bh后1天与3天两个时间点，对感病MLO野生型（MLO WT）与抗病近等基因回交系mlo5的VOC谱进行了时序表征。比较分析结果显示，不同基因型的VOC谱存在显著差异，β-石竹烯、芳樟醇、(Z)-3-己烯醇与水杨酸甲酯的释放量均呈现基因型依赖性变化。进一步通过植株间通讯实验，研究人员将感病大麦暴露于MLO WT或mlo5供体植株的复合VOC混合体系中，在Bh接种抗性试验中发现，受体植物的VOC诱导抗病性依赖于供体植株的基因型。此外，非靶向代谢组学与基因表达研究证实，水杨酸（SA）依赖通路介导了VOC诱导的白粉病抗性。外源施加水杨酸甲酯可上调大麦化学诱导型-4（BARLEY CHEMICALLY INDUCED-4）标记基因的表达，并诱导受体植物产生抗病性。本研究结果表明，在大麦与活体营养型真菌的互作过程中，其VOC谱会发生基因型依赖性改变，且VOC介导的抗病性与水杨酸相关通路共享调控元件。本研究鉴定得到的VOC信号，可作为大麦-白粉病互作系统中病害进程的非侵入性标记，同时也可作为诱导受体植物抗病性的信号分子。