PopW of Ralstonia solanacearum, a new two-domain harpin targeting the plant cell wall.
Harpins are extracellular glycine-rich proteins eliciting a hypersensitive response (HR). In this study, we identified a new harpin, PopW, from Ralstonia solanacearum strain ZJ3721. This 380-amino-acid protein is acidic, rich in glycine and serine, and lacks cysteine. When infiltrated into the leaves of tobacco (non-host), PopW induced a rapid tissue collapse via a heat-stable but protease-sensitive HR-eliciting activity. PopW has an N-terminal harpin domain (residues 1-159) and a C-terminal pectate lyase (PL) domain (residues 160-366); its HR-eliciting activity depends on its N-terminal domain. Analyses of subcellular localization and plasmolysis demonstrated that PopW targeted the onion cell wall. This was further confirmed by its ability to specifically bind to calcium pectate, a major component of the plant cell wall. However, PopW had no detectable PL activity. Western blotting revealed that PopW was secreted by the type III secretion system in an hrpB-dependent manner. Gene sequencing indicated that popW is conserved among 20 diverse strains of R. solanacearum. A popW-deficient mutant retained the ability of wild-type strain ZJ3721 to elicit HR in tobacco and to cause wilt disease in tomato (a host). We conclude that PopW is a new cell wall-associated, hrpB-dependent, two-domain harpin that is conserved across the R. solanacearum species complex.
Li
Jian-Gang
JG
Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Nanjing, China.
Liu
Hong-Xia
HX
Cao
Jing
J
Chen
Li-Feng
LF
Gu
Chun
C
Allen
Caitilyn
C
Guo
Jian-Hua
JH
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D015153:Blotting, Western; D002473:Cell Wall / Q000382:microbiology*; D017124:Conserved Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D008969:Molecular Sequence Data; D010368:Pectins / Q000378:metabolism; D010802:Phylogeny; D018515:Plant Leaves / Q000276:immunology / Q000382:microbiology; D011133:Polysaccharide-Lyases / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D043368:Ralstonia solanacearum / Q000378:metabolism* / Q000472:pathogenicity; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology* / Q000276:immunology / Q000382:microbiology*; D014774:Virulence
D001425:Bacterial Outer Membrane Proteins; C075462:harpin protein, Erwinia amylovora; D010368:Pectins; D011133:Polysaccharide-Lyases; C023911:pectate lyase; C003181:polygalacturonic acid
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