三七根系募集有益微生物降解自毒皂苷的效应和机制

Panax notoginseng is one of the characteristic herbal medicinal plants in China, which cultivated in larg areas with remarkable benefit, but the growth is often hampered by replant failure. Our recent research demonstrated that some kinds of ginsenosides released into the rhizosphere by root secretion or root residue degradation showed allelopathic autotoxicity, which was the most important cause agent of replant failure. However, autotoxicity usually occurred in replant soil to damage next generation plant growth but not occurred during the stage of P. notoginseng growing. To decipher the mechanism of P. notoginseng protect itself from autotoxicity may help us to find new breakthrough to conquer replant failure. The rhizosphere microbial community is referred to as the second genome of the plant, which is crucial for plant to defense biotic or abiotic stress. The rhizosphere microbiome may play an important role in protecting root from autotoxicity through degrading autotoxic ginsensides. In this study, we want to study (1) Whether P. notoginseng can recruit beneficial microbiome to degrade autotoxic ginsenosides? (2) the role and mechanism of root exudates in regulating rhizosphere beneficail microbiome to degrade autotoxic ginsenosides; (3) whether P. notoginseng root can secrete more sustances to recruit rhizosphere microbiome to degrade autotoxic ginsenoside when root stressed by autotoxicity? These studies will help us to understand the effect and mechanism of P. notoginseng root to recruit beneficial rhizosphere microbiome to help itself against autotoxicity. It also benefit us to further understand the mechanism of replant failure and to develop novel techniques to conquer replant failure of P. notoginseng.

三七是我国最具特色的药用植物之一，但连作障碍严重制约三七种植。众多研究表明，三七分泌到土壤中的自毒皂苷是导致下茬三七连作障碍的重要诱因。但三七生长过程中并不表现明显的自毒，仅在三七收获后再植三七才表现明显。探明三七生长期如何抵御根际自毒皂苷的危害可能为克服连作障碍找到新的突破口。根际微生物被认为是植物的第二基因组，在帮助植物抵御生物或非生物逆境过程中起着重要作用。三七根系在生长过程中可能会通过根系分泌物募集有益微生物来抵御自毒危害。因此，本项目拟深入研究①三七根系募集微生物降解根际自毒皂苷的效应；②三七根系分泌物在调控根际降解皂苷功能微生物中的作用和机制；③三七根系在受到自毒皂苷胁迫后是否会刺激根系分泌更多的代谢物来募集降解皂苷的微生物？这些研究有助于阐明三七在生长过程中招募有益微生物降解自毒皂苷的效应和机制，进一步解析三七连作障碍形成的原因，为克服三七自毒效应相关技术的研发提供理论依据。

三七是我国独具特色的大宗药用作物，连作障碍严重制约三七产业的健康发展。前期研究发现三七分泌到土壤中的自毒皂苷是导致下茬连作障碍的重要诱因，但三七生长过程中并不表现自毒，仅在收获后再植三七才表现明显。因此，探明三七如何抵御根际自毒皂苷危害有望为克服三七连作障碍找到新的突破口。本项目深入研究了①根际土壤提取液对自毒皂苷的降解活性，分析了皂苷胁迫下三七根际土壤细菌结构的变化，并从中分离降解自毒皂苷细菌，明确三七在生长过程中选择性地募集有益微生物降解自毒皂苷的效应。②在自毒皂苷胁迫下，三七根系代谢、根系分泌物和根际微生物结构和功能的变化及相关性，解析三七根系募集有益微生物降解自毒皂苷的机制。主要进展和研究成果如下：. （1）明确了三七根际土壤中存在降解自毒皂苷的微生物，且在自毒皂苷胁迫下，三七根系选择性地富集伯克氏菌来降解根际自毒皂苷。. （2）明确了伯克氏菌B36既能利用皂苷生长，又能与皂苷协同增强B36菌株对锈腐菌的拮抗活性及其在三七根际的定殖能力，具有较好的缓解三七连作障碍的效果。. （3）皂苷胁迫下三七根系募集伯克氏菌的机制在于一方面皂苷胁迫能诱导三七根系转录水平发生显著变化，并促进次生代谢产物的生物合成和ABC转运蛋白代谢路径的改变，导致羽扇豆酮、肉桂酸、愈伤酸、三七皂苷R1、γ-氨基丁酸和12-氧-植物二烯酸的分泌增加；对香豆酸甲酯、葡萄糖酸、甘磷酸胆碱、4-甲氧基肉桂酸和D-阿拉伯糖醇的分泌减少。另一方面显著变化的代谢物中三七皂苷R1、肉桂酸、甘磷酸胆碱、葡萄糖酸和D-阿拉伯糖醇在较低浓度范围内对根际降解皂苷的细菌具有明显的吸引作用；羽扇豆酮和D-阿拉伯糖醇能通过促进细菌生长和生物膜的形成来促进降解皂苷菌株在土壤中的生长和定殖。. 研究结果首次系统解析了自毒皂苷胁迫后三七根系调控微生物抵御自毒危害的效应和机制，为利用根系代谢物定向调控根际降解皂苷菌株，缓解三七连作障碍提供了重要理论依据。