title: Disruption of gene pqqA or pqqB reduces plant growth promotion activity and biocontrol of crown gall disease by Rahnella aquatilis HX2.
abstract: Rahnella aquatilis strain HX2 has the ability to promote maize growth and suppress sunflower crown gall disease caused by Agrobacterium vitis, A. tumefaciens, and A. rhizogenes. Pyrroloquinoline quinone (PQQ), a cofactor of aldose and alcohol dehydrogenases, is required for the synthesis of an antibacterial substance, gluconic acid, by HX2. Mutants of HX2 unable to produce PQQ were obtained by in-frame deletion of either the pqqA or pqqB gene. In this study, we report the independent functions of pqqA and pqqB genes in relation to PQQ synthesis. Interestingly, both the pqqA and pqqB mutants of R. aquatilis eliminated the ability of strain HX2 to produce antibacterial substance, which in turn, reduced the effectiveness of the strain for biological control of sunflower crown gall disease. The mutation also resulted in decreased mineral phosphate solubilization by HX2, which reduced the efficacy of this strain as a biological fertilizer. These functions were restored by complementation with the wild-type pqq gene cluster. Additionally, the phenotypes of HX2 derivatives, including colony morphology, growth dynamic, and pH change of culture medium were impacted to different extents. Our findings suggested that pqqA and pqqB genes individually play important functions in PQQ biosynthesis and are required for antibacterial activity and phosphorous solubilization. These traits are essential for R. aquatilis efficacy as a biological control and plant growth promoting strain. This study enhances our fundamental understanding of the biosynthesis of an environmentally significant cofactor produced by a promising biocontrol and biological fertilizer strain.
authors.affiliation: Department of Ecological Science and Engineering, College of Resources and Environmental Sciences, China Agricultural University, Beijing, China; Beijing Key Laboratory of Biodiversity and Organic Farming, China Agricultural University, Beijing, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Li
authors.affiliation: College of Chemistry and Biological Sciences, Yi Li Normal University, Yining, Xinjiang, China.
authors.forename: Ziwei
authors.initials: Z
authors.lastname: Jiao
authors.affiliation: Department of Environmental Sciences, University of California Riverside, Riverside, California, United States of America.
authors.forename: Lauren
authors.initials: L
authors.lastname: Hale
authors.affiliation: Department of Ecological Science and Engineering, College of Resources and Environmental Sciences, China Agricultural University, Beijing, China; Beijing Key Laboratory of Biodiversity and Organic Farming, China Agricultural University, Beijing, China.
authors.forename: Wenliang
authors.initials: W
authors.lastname: Wu
authors.affiliation: Department of Ecological Science and Engineering, College of Resources and Environmental Sciences, China Agricultural University, Beijing, China; Beijing Key Laboratory of Biodiversity and Organic Farming, China Agricultural University, Beijing, China.
authors.forename: Yanbin
authors.initials: Y
authors.lastname: Guo
mesh_terms: D000595:Amino Acid Sequence; D006368:Helianthus / Q000235:genetics* / Q000254:growth & development / Q000382:microbiology; D009154:Mutation; D045542:PQQ Cofactor / Q000096:biosynthesis / Q000235:genetics*; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010941:Plant Tumors / Q000235:genetics* / Q000382:microbiology; D020638:Rahnella / Q000235:genetics* / Q000472:pathogenicity
chemical_list: D045542:PQQ Cofactor