调控基因gacA在荧光假单胞菌2P24防治土传病害中的作用

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

Pseudomonasfluorescens 2 P2 4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PM3 3 90 ,其表现型与调控基因 gac A的突变体表型相似。通过 PCR介导的文库筛选方法 ,从 2 P2 4基因组文库中获得 2个含有 gac A基因的阳性克隆 ,进一步亚克隆 ,得到只含有完整 gac A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 ,gac A- 突变菌株与野生型 2 P2 4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 gac A在 2 P2 4中具有整体水平的调控功能 ,并在 2 P2 4防治土传病害中起到重要的作用。

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.