Identification of novel Ralstonia solanacearum type III effector proteins through translocation analysis of hrpB-regulated gene products.
The Hrp type III secretion system (TTSS) is essential for the pathogenicity of Ralstonia solanacearum on host plants. Hrp TTSS is a specialized secretion system that injects virulence proteins, the so-called type III effector proteins, into plant cells. In R. solanacearum, the expression of Hrp TTSS-related genes is regulated by an AraC-type transcriptional activator, HrpB. We have identified 30 hrpB-regulated hpx (hrpB-dependent expression) genes and three well-known hrpB-regulated genes, popA, popB and popC, as candidate effector genes in R. solanacearum strain RS1000. In this study, we newly cloned 11 additional candidate effector genes that share homology with known hpx genes from R. solanacearum RS1000. Using a Cya reporter system, we investigated the translocation of these 44 gene products into plant cells via the Hrp TTSS and identified 34 effector proteins. These include three effector families composed of more than four members, namely the Hpx4, Hpx30 and GALA families. The Hpx30 family effectors are 2200-2500 aa in size and appear to be the largest class of effector proteins among animal- and plant-pathogenic bacteria. Members of this family contain 12-18 tandem repeats of a novel 42 aa motif, designated SKWP repeats.
Mukaihara
Takafumi
T
Research Institute for Biological Sciences, Okayama (RIBS), 7549-1 Yoshikawa, Kibichuo-cho, Okayama 716-1241, Japan.
Tamura
Naoyuki
N
Research Institute for Biological Sciences, Okayama (RIBS), 7549-1 Yoshikawa, Kibichuo-cho, Okayama 716-1241, Japan.
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005798:Genes, Bacterial; D017930:Genes, Reporter; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology*; D021381:Protein Transport; D043368:Ralstonia solanacearum / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D017422:Sequence Analysis, DNA; D032323:Solanum melongena / Q000382:microbiology*; D014157:Transcription Factors / Q000378:metabolism*; D014774:Virulence
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C079047:hrpB protein, Ralstonia solanacearum