Liu Yunpeng, Chen Lin, Zhang Nan, Li Zunfeng, Zhang Guishan, Xu Yu, Shen Qirong, Zhang Ruifu
1 Key Laboratory of Microbial Resources Collection and Preservation, Ministry of Agriculture, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, P.R. China; and.
2 Jiangsu Key Lab and Engineering Center for Solid Organic Waste Utilization, National Engineering Research Center for Organic-based Fertilizers, Nanjing Agricultural University, Nanjing, 210095, P.R. China.
Mol Plant Microbe Interact. 2016 Apr;29(4):324-30. doi: 10.1094/MPMI-10-15-0239-R. Epub 2016 Mar 14.
Mechanisms by which beneficial rhizobacteria promote plant growth include tryptophan-dependent indole-3-acetic acid (IAA) synthesis. The abundance of tryptophan in the rhizosphere, however, may influence the level of benefit provided by IAA-producing rhizobacteria. This study examined the cucumber-Bacillus amyloliquefaciens SQR9 system and found that SQR9, a bacterium previously shown to enhance the growth of cucumber, increased root secretion of tryptophan by three- to fourfold. Using a split-root system, SQR9 colonization of roots in one chamber not only increased tryptophan secretion from the noninoculated roots but also increased the expression of the cucumber tryptophan transport gene but not the anthranilate synthesis gene in those roots. The increased tryptophan in isolated rhizosphere exudates was sufficient to support increased IAA production by SQR9. Moreover, SQR9 colonization of roots in one chamber in the split-root system resulted in sufficient tryptophan production by the other roots to upregulate SQR9 IAA biosynthesis genes, including a 27-fold increase in the indole-3-acetonitrilase gene yhcX during subsequent colonization of those roots. Deletion of yhcX eliminated SQR9-mediated increases in root surface area, likely by reducing IAA-stimulated lateral root growth. This study demonstrates a chemical dialogue between B. amyloliquefaciens and cucumber in which this communication contributes to bacteria-mediated plant-growth enhancement.
有益根际细菌促进植物生长的机制包括依赖色氨酸的吲哚-3-乙酸（IAA）合成。然而，根际中色氨酸的丰度可能会影响产IAA根际细菌提供的益处水平。本研究考察了黄瓜-解淀粉芽孢杆菌SQR9系统，发现SQR9（一种先前已证明能促进黄瓜生长的细菌）使根中色氨酸的分泌增加了三到四倍。利用分根系统，一个隔室中根系的SQR9定殖不仅增加了未接种根系中色氨酸的分泌，还增加了黄瓜色氨酸转运基因的表达，但未增加这些根系中邻氨基苯甲酸合成基因的表达。分离的根际分泌物中色氨酸的增加足以支持SQR9产生更多的IAA。此外，分根系统中一个隔室中根系的SQR9定殖导致其他根系产生足够的色氨酸，从而上调SQR9的IAA生物合成基因，包括在随后这些根系定殖期间吲哚-3-乙腈酶基因yhcX增加了27倍。yhcX的缺失消除了SQR9介导的根表面积增加，这可能是通过减少IAA刺激的侧根生长实现的。本研究证明了解淀粉芽孢杆菌与黄瓜之间的化学对话，其中这种交流有助于细菌介导的植物生长增强。
