植物根系代谢物是植物-微生物互作的桥梁纽带,作为信号物质和微生物营养源调控着微生物的群落结构和多样性,而根区微生物区系的改变则反作用于植物的生长、发育和抗性。本文聚焦植物根系代谢物介导的植物-微生物互作,梳理了植物-微生物互作研究中次级代谢物的种类、作用及其检测手段;探讨了植物通过调节自身代谢物以适应品种进化及繁衍后代过程中发挥的功能作用;阐述了逆境胁迫下植物利用根系代谢物招募特异微生物(解磷、溶磷)或者有益微生物促进自身生长以缓解胁迫压力的机制;分析了根系代谢物作为信号物质诱导植物抗病的方式“求救假说”,为可持续农业发展提供思路和理论依据。
Plant metabolites exuded from roots have been identified as a bridge in plant-microbe interaction, and as a signal player in regulating the structure and diversity of soil microbial community. The altered soil microbial community served as feedback to the plant, resulting in promotion of plant growth, development and resistance. In this article, we reviewed recent advances on plant-microbe interaction mediated by plant metabolites, and sketched the category, function and testing method of the secondary metabolites in the above interaction process. Additionally, we investigated how plants developed themselves in order to adapt to the cultivar evolution and the reproduction by regulating their root metabolites, and illuminated the mechanisms of plants recruiting specific or beneficial microorganisms to the rhizosphere to improve their development and therefore alleviate the biotic and abiotic stresses. Furthermore, the "cry for help" strategy that plants recruit beneficial microbes or traits from the environment using a range of chemical stimuli to enhance their resistance was analyzed. This paper provided ideas and theoretical support for the sustainable agricultural development.
植物体内蕴含着丰富的次级代谢物,约20多万种,这些代谢物在植物生长和发育中起着重要的作用,尤其在植物与微生物的互作中扮演着重要的角色。植物生长在土壤中,植物根系除了固着植物并作为吸收水分和营养的器官外,还是微生物聚集栖息和繁衍的场所,而植物根系代谢物作为植物体内核心物质,可以通过根系在土壤中的分布影响植物的根际微生物组来达到优化土壤条件、吸收养分和提高抗性的功能[
植物根系代谢物分为初级代谢物和次级代谢物;植物初级代谢物指参与植物生长代谢、维持生命活动的主要能源物质,包括糖类、脂类、氨基酸、核酸等大分子化合物;植物次级代谢途径产生的物质统称为次级代谢产物,它与初级代谢产物不同,它并不是植物生长和发育所必需的小分子物质,且根据次级代谢途径不同,可以将其分为酚酸类、萜烯类、类黄酮、类固醇和生物碱类等[
目前,植物次级代谢在植物-微生物的互作中起着重要的作用[
代谢组学的发展为根际微生物的研究提供了新思路,且着重于研究根系代谢物作为碳源为特定微生物群体提供营养,从而鉴定出特异微生物对代谢物基质的偏好。但是,在广阔的空间中追踪植物-微生物互作的活性物质还是受到技术的限制,目前仅有跟踪根际微生物互作系统(track root interactions system,TRIS)[
据统计,植物中25%以上的光合作用产物以糖、氨基酸、有机酸、根际沉积物等各种各样的碳源化合物形式通过植物根系在植物根际沉积下来[
植物根系在土壤中除了固着植物并作为吸收水分和营养的器官外,还是微生物聚集栖息和繁衍的场所,植物代谢物作为碳源调控地下根际微生物群落结构来响应生物和非生物胁迫,例如当拟南芥植物受到外界环境的影响时,通过改变根系特异代谢物(二半萜化合物)的合成能力,使自身特异的代谢物在根际积累来调控根际微生物组[
根系代谢物是土壤微生物的重要碳源,为筛选土壤的微生物菌群提供了天然培养基,因此根系代谢物是根际微生物的调控者,可以通过改变根系代谢物的分泌种类或者模式来选择一个良好的根际微生物群落,这可能为提高植物抗性开辟新的机会,从而促进作物生长[
植物体内一些代谢物质作为信号物质发生转化以响应干旱的胁迫,例如β-环柠檬醛(beta-cyclocitral,BCC)是β-胡萝卜素的氧化产物,可以诱导拟南芥、水稻、番茄主根和须根细胞的分裂速度来调节根系的生长[
众所周知,矿质元素是植物生长必需的营养元素,面对低磷、低钾等胁迫时,植株是否会调整自身代谢物质来调控根际微生物来响应胁迫呢?有研究报道,缺铁可以诱导拟南芥分泌香豆素,这种代谢物不仅可以增强固定铁源的可移动性从而满足植物对铁的需求[
磷是植物生长必需的三大要素之一,土壤缺磷是世界范围内普遍存在的问题,会严重制约植株的生长[
禾本科植物在营养胁迫条件下会分泌一种非蛋白质组分的氨基酸—麦根酸类植物高铁载体,它对微量元素螯合效率极高,它的合成、分泌、螯合和吸收是禾本科作物适应缺铁环境的反应[
根际微生物群落中有些微生物是有益的,但有些微生物却严重影响着植物的健康,例如尖孢镰刀菌。尖孢镰刀菌趋向于宿主植物与根系释放出的代谢物质有关,这种趋化型反应需要保守的信号传导成分,包括Ste2,NADPH氧化酶B (NotB)复合物[
大量的试验表明,植物根际、叶际、花际是植物与微生物互作的共同体,不仅仅是一种简单的“租客”关系,更多的是关系到植物的互作和植物的免疫系统,进而影响植物的生长和发展[
国内外研究表明,植物可以招募有益微生物到植物根际以抵抗病原菌的入侵,例如拟南芥可以招募3种细菌到植物根际,促进植物叶部免受病原菌侵染[
植物通过改变周围土壤环境影响自身或在该土壤中生长的下一代植物的生长、发育、新陈代谢、对生物和非生物胁迫的防御或耐受性等性能被称为植物-土壤反馈(plant-soil feedbacks)。根系代谢物可以通过塑造根际微生物驱动土壤对植物生长和防御的反馈[
目前植物-土壤-微生物互作是目前研究的热点,尤其微生物组和代谢组的研究,这为解密地下和地上植株互作的“黑匣子”奠定了基础,但是目前研究尚处于初级阶段,缺乏深入分析互作关系的机理研究,尤其微生物的功能预测更需要进一步研究。
大量的研究专注于植物-微生物的互作中微生物的变化趋势,缺乏更深层次的挖掘,例如植物-植物互作中,根系代谢物介导的微生物改变会导致植物基因型的改变和防御响应,而这反应会引起后代在时间和空间上更大尺度的级联效应,从而达到防御效果。这些不仅为以后育种提供了新思路,还为绿色农业发展提供了新思想。
植物代谢物作为信号物质承载着植物与土壤微生物互作的桥梁和纽带,因此根系代谢物介导的植物-根际微生物互作研究较多,对以后有效的预测微生物对植株健康生长的指数提供了理论支撑。但是,如何阐明根系代谢物质介导的微生物区系-植物表征的偶联机制是目前研究的瓶颈问题,因此综合利用代谢组学和宏基因组学结合合成微生物(SynComs),系统认识植物物种的微生物群,以确定核心和枢纽微生物区系以及其提供宿主的功能才是解决瓶颈问题的关键。
建立植物代谢与土壤微生物功能的诊断体系。植物根系代谢物为根际微生物提供了碳源,形成了不同的微生物区系结构,这些微生物区系的变化可能会影响微生物群落的稳定性和对未来恢复能力的干扰。因此,要重点关注微生物群落的特定功能特征,如快速增长、环境特性等等,建立植物代谢与土壤微生物功能的诊断体系可以帮助预测土壤微生物群落将如何应对不同气候环境的胁迫和对病原菌的抵御能力。
综上所述,综合解析植物-微生物互作体系,利用植物微生物组和代谢组研究植物-微生物互作为植物病害的控制提供了切入点,为未来某一或某些菌的生防功能预测和生物防治提供了着力点,也为作物种植中土壤微生物功能预测提供了新方法和新思路。
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