Type III secretion system is an essential pathogenic factor in poplar canker pathogen Lonsdalea quercina
Аннотация
Poplar canker caused by Lonsdalea quercina(formerly Brenneria quercina or Erwinia quercina) was found in Henan Province,China in 2005.The disease affected local poplar industry seriously.Bacterial strain N-5-1 was isolated from naturally infected poplar and identified as the pathogen of canker disease.Based on gene sequence alignment,a complete type Ⅲ secretion system(T3SS) cluster,similar to that in pathogenic bacteria Dickeya dadantii 3937 and Erwinia amylovora CFBP1430,was identified in the genome sequence of strain N-5-1.The T3 SS of N-5-1 had about 23 kb in size including 26 genes,9 of which were highly conserved hrc genes.To study the role of T3 SS in pathogenicity of strain N-5-1,a deletion mutant of the T3 SS structural gene hrcV and its complemented mutant were constructed.Pathogenicity assay on poplar branches(Populus × eu—ramericana Zhonglin 46) indicated that the AhrcV mutant was significantly less virulent(disease index 33.3)than its parent,while the complemented mutant HBhrcV restored the virulence to the wild-type level(disease indexes were 85.6 and 83.3,respectively).The hrcV mutation abolished the HR elicitation activity on tabacco,Poplar canker caused by Lonsdalea quercina( formerly Brenneria quercina or Erwinia quercina) w as found in Henan Province,China in 2005. The disease affected local poplar industry seriously. Bacterial strain N-5-1 w as isolated from naturally infected poplar and identified as the pathogen of canker disease. Based on gene sequence alignment,a complete type III secretion system( T3SS) cluster,similar to that in pathogenic bacteria Dickeya dadantii 3937 and Erwinia amylovora CFBP1430,w as identified in the genome sequence of strain N-5-1. The T3 SS of N-5-1 had about 23 kb in size including 26 genes,9 of w hich w ere highly conserved hrc genes. To study the role of T3 SS in pathogenicity of strain N-5-1,a deletion mutant of the T3 SS structural gene hrc V and its complemented mutant w ere constructed. Pathogenicity assay on poplar branches( Populus × euramericana ‘Zhonglin 46') indicated that the Δhrc V mutant w as significantly less virulent( disease index 33. 3)than its parent,w hile the complemented mutant HBhrc V restored the virulence to the w ild-type level( disease indexes w ere 85. 6 and 83. 3,respectively). The hrc V mutation abolished the HR elicitation activity on tabacco,but did not influence the bacterial grow th,motility and biofilm formation. This study suggests that the T3 SS is an essential pathogenic factor in L. quercina N-5-1.