根际有益菌在作物根表形成生物膜的机理模型与调控研究

Application of plant growth-promoting rhizobacteria (PGPR) in stimulation of plant growth and suppression of soil-borne diseases is receiving more and more attention. Effective application of PGPR is an important strategy for decreasing of chemicals input. Efficient colonization of beneficial microbes on plant roots or rhizosphere plays vital role for their function performance. Bacillus spp. hold a complex regulation model for biofilm formation, as the signal molecular in the root exudates of plant could affect the colonization behavior of Bacillus by regulating their biofilm formation. Bacillus amyloliquefacien SQR9 (SQR9) has been screened and successfully used as a PGPR in bio-organic fertilizers. The strain can significantly promote plant growth and has a high antagonistic ability to soil-born pathogens as well. This project will study the rhizosphere colonization of SQR9 in different plants, such as cucumber, maize, and banana and biocontrol behavior of its differernt mutants (the mutants with different phosphorylation level of DegU, deficient of abrB, deficient of bmyD, and so on). The influence and related mechanism of different phosphorylation level of DegU, transcription factor AbrB, as well as other regulators on biofilm formation of SQR9 will be evaluated. The interaction mechanism between root exudates and the several mutants will also be investigated, especially on the roles of different root exudates on the transcriptional profiling of SQR9 and the mutants. The main goal of this study is to reveal the detailed molecular mechanism regarding colonization and biofilm formation of SQR9 on plant roots. This research will provide the theoretical instructions for improving the root colonization and agricultural application of SQR9. Also we can provide domestic researchers with molecular technology on PGPR.

根际有益菌在促进植物生长及防控土传病害方面的应用日益受到重视，施用根际有益菌是减少农用化学品投入的重要途径之一，有益菌在植物根际的有效定殖和成膜是其发挥功能的前提。芽孢杆菌拥有一整套复杂的生物膜形成调控机制，而根系分泌物中的信号分子能通过调控其生物膜形成而影响根际定殖和成膜行为。本项目以实验室分离并已广泛应用的根际有益菌Bacillus amyloliquefacien SQR9（SQR9）为材料，研究其不同突变体在不同作物根系的定殖和成膜特征，及其促生和防控土传病害的效果；DegU不同磷酸化水平、转录因子AbrB及其他因子在SQR9成膜中的分子机制及与根系分泌物的互作效应；SQR9及突变体响应不同作物根系分泌物的转录组差异。揭示根系分泌物调控SQR9在作物根表定殖及成膜的分子机理模型，为增强SQR9在根际的定殖和成膜能力提供理论依据，也为国内开展PGPR的分子研究提供思路与技术支撑。

根际有益菌在促进植物生长及防控植物土传病害方面的应用日益受到重视，施用根际有益菌是减少农用化学品投入的重要途径之一，而有益菌在植物根际的有效定殖和成膜是其发挥功能的前提。本项目以分别以一株典型的根际有益解淀粉芽孢杆菌SQR9和一株生防哈茨木霉NJAU 4742为研究对象，从菌株的生物膜形成、重寄生作用、与植物根系互作及根际定殖等方面展开研究，以期揭示根际有益菌在作物根表形成生物膜的机理模型，获得以下重要结果：1）有益菌SQR9中全局性调控蛋白DegU的磷酸化水平可影响菌株成膜与根际定殖能力，构建了比野生型具更强根际定殖能力的木糖诱导型基因工程菌SQR9XYQ；两组分调控系统ResDE、ABC转运蛋白FtsEX及磷壁酸合成相关蛋白（GgaA和GtaB）均是影响SQR9生物膜形成的调控因子，其中ResDE感受氧分压降低的信号后，通过调控呼吸链并借助组氨酸激酶KinB调控成膜，FtsEX亦通过与激酶KinB/KinD互作影响成膜，磷壁酸合成相关蛋白通过影响胞外多糖合成调控成膜。2）转录组分析表明植物根系分泌物可通过激活细胞生长代谢和促进胞外基质合成两种方式诱导菌株SQR9的生物膜形成，根系分泌物（小分子有机酸等）和脱落物（植物多糖等）分别通过全局性调控因子Spo0A和DegU调控菌株SQR9的生物膜形成和根际定殖。3）生防哈茨木霉菌NJAU 4742重寄生植物病原真菌的机制是分泌中性金属肽酶NMP1和产生活性氧。4）哈茨木霉NJAU 4742中疏水小蛋白（hydrophobin，HFB）家族的HFB4、HFB8和HFB15可影响菌株与植物根系的互作及根际定殖，初步阐明其功能特性。5）哈茨木霉NJAU 4742可通过调控植物体内的生长素合成与转运促进植株生长，通过糖苷酶等外泌蛋白刺激植物防御激素茉莉酸（jasmonic acid，JA）和乙烯（ethylene，ET）途径诱导植物的系统抗性（induced systemic resistance，ISR）。以上结果揭示了典型有益菌在作物根表定殖及成膜的分子机理模型，为增强有益菌的根际定殖能力和应用效果提供了理论依据，也为国内开展相关菌株的分子生物学研究提供了思路与技术支撑。