调控基因gacA在荧光假单胞菌2P24防治土传病害中的作用

 Pseudomonas fluorescens 2P24分离自山东小麦全蚀病自然衰退土壤,该菌株能产生抗生素2,4-二乙酰基藤黄酚(2,4-diacetylphloroglucinol,2,4-DAPG)、氢氰酸,嗜铁素和蛋白酶,且抑菌谱广,可防治多种作物土传病害。本研究应用Tn5转座突变技术,获得1株产嗜铁素过量,同时不产生2,4-DAPG、HCN、蛋白酶、不能形成生物膜(biofilm)的突变菌株PM3390,其表现型与调控基因gacA的突变体表型相似。通过PCR介导的文库筛选方法,从2P24基因组文库中获得2个含有gacA基因的阳性克隆,进一步亚克隆,得到只含有完整gacA开放阅读框的1.2 kb片段,互补实验表明其能恢复突变菌株的多种缺失表型。生测结果表明,gacA-突变菌株与野生型2P24相比,对不同土传病害的生防效果均显著降低。以上结果证实gacA在2P24中具有整体水平的调控功能,并在2P24防治土传病害中起到重要的作用。

The role of regulatory gene gacA in the suppression of soil-borne diseases by Pseudomonas fluorescens 2P24

Pseudomonas fluorescens 2P24, a biocontrol agent isolated from suppressive soil of wheat take-all disease, protects plants against soil-borne diseases. This strain produces several antibiotic secondary metabolites, such as 2,4-diacetylphloroglucinol (2,4-DAPG), hydrogen cyanide (HCN), siderophore and proteases. A mutant strain PM3390 obtained by Tn5 mutagenesis showed pleiotropic changes on the production of secondary metabolites including overproduction of siderophore and nonproduction of 2,4-DAPG, HCN and protease. PM3390 was also unable to form biofilm. These phenotypes were complemented by a 1.2 kb DNA fragment obtained from the genomic DNA library of P. fluorescens 2P24. Sequence analysis revealed a 642 bp open reading frame (ORF) which was highly homologous to the response regulator gene gacA. In greenhouse, the gacA-negative mutant showed decreased ability to suppress soil-borne diseases compared with that of wild type 2P24. The results revealed that gacA gene, a global regulator in the P. fluorescens 2P24, played an important role in biocontrol of soil-borne plant diseases.