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Published on November 30, 2007; 10.1104/pp.107.112748

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Received November 6, 2007
Accepted November 20, 2007

Pyrroloquinoline quinone is a plant growth promotion factor produced by Pseudomonas fluorescens B16

Okhee Choi , Jinwoo Kim , Jung-Gun Kim , Yeonhwa Jeong , Jae Sun Moon , Chang Seuk Park , and Ingyu Hwang *

Department of Agricultural Biotechnology and Center for Agricultural Biomaterials, Seoul National University, Seoul 151-921, Korea; Division of Plant Resources and Environment, Gyeongsang National University, Jinju 660-701, Korea; Plant Genome Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon 305-333, Korea

* Corresponding author; email: ingyu{at}snu.ac.kr.

Pseudomonas fluorescens B16 is a plant growth-promoting rhizobacterium. To determine the factors involved in plant growth promotion by this organism, we mutagenized the wild-type strain B16 using {Omega}Km elements and isolated one mutant, K818, which is defective in plant growth promotion, in a rockwool culture system. A cosmid clone, pOK40, which complements the mutant K818, was isolated from a genomic library of the parent strain. Tn3-gusA mutagenesis of pOK40 revealed that the genes responsible for plant growth promotion reside in a 13.3-kb BamHI fragment. Analysis of the DNA sequence of the fragment identified 11 putative open reading frames, consisting of seven known and four previously unidentified pyrroloquinoline quinone (PQQ) biosynthetic genes. All of the pqq genes showed expression only in nutrient-limiting conditions in a PqqH-dependent manner. Electrospray ionization mass spectrometry analysis of culture filtrates confirmed that the wild-type B16 produces PQQ, whereas the mutants defective in plant growth promotion do not. Application of the wild-type B16 on tomato plants cultivated in a hydroponic culture system significantly increased the height, flower number, fruit number, and total fruit weight, whereas none of the strains that did not produce PQQ promoted tomato growth. Furthermore, 5–1000 nM of synthetic PQQ conferred a significant increase in the fresh weight of cucumber seedlings, confirming that PQQ is a plant growth promotion factor. Treatment of cucumber leaf discs with PQQ and the wild-type B16 resulted in the scavenging of reactive oxygen species and H2O2, suggesting that PQQ acts as an antioxidant in plants.






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