根际促生菌Bacillus amyloliquefaciens SQR9与植物根系分泌物互作的分子机理研究

Utilization of rhizospheric beneficial microbes for plant growth promotion and soil-borne diseases control has been paid more attentions. Efficient colonization of beneficial microbes on plant root plays vital role for their function performance, as the "language" of the plant to interact with other organisms, root exudates are the source of signals which regulate the interactions between bacteria and plants in rhizoshpere. This proposal will use beneficial strain Bacillus amyloliquefacien SQR9 as the model to investigate the molecular mechanism of its interaction with cucumber root exudates. B. amyloliquefacien SQR9 was isolated by our lab from the healthy cucumber rhizoshpere and applied in agricultural practice as the biofertilizer and biocontrol agent. B. amyloliquefacien SQR9 was a strong colonizer of cucumber root, and performed well for biofilm formation, chemotaxis activity and multiple antagnistic metabolites secretion, B. amyloliquefacien SQR9 showed positive chemotaxis response toward cucumber root exudates, which also increased the biofilm formation of B. amyloliquefacien SQR9. This study will investigate the effect of B. amyloliquefacien SQR9 colonization on the cucumber root exudates and its biological meaning, identify the signals of the root exudates which regulate the root colonization of B. amyloliquefacien SQR9, screen the genes in B. amyloliquefacien SQR9 genome which were regulated by the identified signals, study their roles in the colonizing process, elucidate their response mechnisms to the identified signals. This research will provide the theoretical instructions for improving the root colonization and agricultural application of B. amyloliquefacien SQR9.

根际有益微生物在促进植物生长及拮抗土传病害方面的应用日益受到重视，有效的根际定殖是其功能发挥的关键因素，根系分泌物作为植物与其他生物交流的"语言"，是根际环境中菌-植互作的信号分子的来源。本申请以实验室分离保存并获得实际应用的根际有益菌株Bacillus amyloliquefacien SQR9为材料，研究其与黄瓜根系分泌物互作的分子机理。SQR9表现了优异的根际定殖、生物膜形成、趋化性、多种拮抗物质分泌等性状，黄瓜根系分泌物能增强该菌的生物膜形成能力和趋化性。本研究拟阐释SQR9定殖对黄瓜根系分泌物组份的影响及其生物学意义，筛选黄瓜根系分泌物中调控SQR9根际定殖的信号分子，克隆鉴定SQR9中受信号分子调控的基因及其在根际定殖中的作用，以及它们响应信号分子的调控机制。为进一步增强B. amyloliquefacien SQR9在根际的定殖能力、更好的发挥其农业应用效果提供理论依据。

根际有益微生物在促进植物生长及拮抗土传病害方面的应用日益受到重视，有效的根际定殖是其功能发挥的关键因素，根系分泌物作为植物与其他生物交流的“语言”，是根际环境中菌-植互作的信号分子的来源。本研究通过对根际促生菌Bacillus amyloliquefaciens SQR9与根系互作的机制研究，获得了以下主要结果：.1、根系分泌物中影响Bacillus amyloliquefaciens SQR9根际定殖的信号分子的鉴定。发现在根际预接种Bacillus amyloliquefaciens SQR9和土传病原真菌Fusarium oxysporumf. sp. cucumerinum（FOC）能够促进后续SQR9的根际定殖，并且抑制FOC的定殖。对黄瓜根系分泌物进行了分析，并鉴定到109种物质。将各个物质与SQR9和FOC的根际定殖结果进行相关性分析并通过纯品外源添加实验发现，SQR9在黄瓜根部定殖后，引起黄瓜分泌更多的色氨酸而进一步促进自身的定殖；同时降低根系分泌物中的棉籽糖含量，减少FOC的定殖；当FOC在黄瓜根部侵染后，黄瓜根系分泌出更多的柠檬酸、延胡索酸和色氨酸以募集更多SQR9到根部定殖，以抵抗FOC对黄瓜的侵染；同时降低棉籽糖含量，减少FOC的后续定殖。.2、根系分泌物影响SQR9根际定殖的分子机制。检测了根系分泌物对SQR9转录组的影响。研究表明，植物能够通过分泌有机酸，如柠檬酸、延胡索酸等，来大幅度改变SQR9的基因表达水平，在定殖前期提高SQR9与趋化作用相关基因的表达，吸引SQR9到根表，然后促进其生物膜形成和抗生素合成相关的基因表达，增强其根际定殖能力和根表竞争能力。通过比较SQR9在根际定殖和浮游生长状态下的蛋白质组差异，发现ResE在根际定殖的SQR9中的含量升高了100倍。ResE能通过调控spo0A、sinI和yqxM的转录来影响SQR9的根际定殖，调控因子abrB能够通过调控生物膜形成来调节SQR9的根际定殖。.3、根系分泌物介导根际促生的互作模型研究。发现黄瓜和SQR9之间存在微妙的相互作用：植物感受到SQR9的根部定殖后，分泌更多的色氨酸，以供给SQR9合成更多的IAA，进而促进自身的生长。.本研究成果为进一步增强SQR9在根际的定殖能力、更好的发挥其农业应用效果提供理论依据。

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