title: Plant-Microbe Communication Enhances Auxin Biosynthesis by a Root-Associated Bacterium, Bacillus amyloliquefaciens SQR9.
abstract: 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.
authors.affiliation: 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.
authors.forename: Yunpeng
authors.initials: Y
authors.lastname: Liu
authors.affiliation: 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.
authors.forename: Lin
authors.initials: L
authors.lastname: Chen
authors.affiliation: 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.
authors.forename: Nan
authors.initials: N
authors.lastname: Zhang
authors.affiliation: 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.
authors.forename: Zunfeng
authors.initials: Z
authors.lastname: Li
authors.affiliation: 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.
authors.forename: Guishan
authors.initials: G
authors.lastname: Zhang
authors.affiliation: 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.
authors.forename: Yu
authors.initials: Y
authors.lastname: Xu
authors.affiliation: 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.
authors.forename: Qirong
authors.initials: Q
authors.lastname: Shen
authors.affiliation: 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.
authors.forename: Ruifu
authors.initials: R
authors.lastname: Zhang
mesh_terms: D001407:Bacillus / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018553:Cucumis sativus / Q000737:chemistry / Q000254:growth & development / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D007210:Indoleacetic Acids / Q000378:metabolism*; D053147:Plant Exudates / Q000737:chemistry; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000737:chemistry / Q000254:growth & development / Q000382:microbiology; D058441:Rhizosphere; D014364:Tryptophan / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D007210:Indoleacetic Acids; D053147:Plant Exudates; D010937:Plant Growth Regulators; C030737:indoleacetic acid; D014364:Tryptophan