Separable roles of the Pseudomonas syringae pv. phaseolicola accessory protein HrpZ1 in ion-conducting pore formation and activation of plant immunity.
The HrpZ1 gene product from phytopathogenic Pseudomonas syringae is secreted in a type-III secretion system-dependent manner during plant infection. The ability of HrpZ1 to form ion-conducting pores is proposed to contribute to bacterial effector delivery into host cells, or may facilitate the nutrition of bacteria in the apoplast. Furthermore, HrpZ1 is reminiscent of a pathogen-associated molecular pattern (PAMP) that triggers immunity-associated responses in a variety of plants. Here, we provide evidence that the ion pore formation and immune activation activities of HrpZ1 have different structure requirements. All HrpZ1 orthologous proteins tested possess pore formation activities, but some of these proteins fail to trigger plant defense-associated responses. In addition, a C-terminal fragment of HrpZ1 retains the ability to activate plant immunity, whereas ion pore formation requires intact HrpZ1. Random insertion mutagenesis of HrpZ1 further revealed the C terminus to be important for the PAMP activity of the protein. HrpZ1 binds to plant membranes with high affinity and specificity, suggesting that the activation of plant immunity-associated responses by HrpZ1 is receptor-mediated. Our data are consistent with dual roles of HrpZ1 as a virulence factor affecting host membrane integrity, and as a microbial pattern governing the activation of plant immunity during infection.
Engelhardt
Stefan
S
Center for Plant Molecular Biology-Plant Biochemistry, University of Tübingen, Tübingen, Germany.
Lee
Justin
J
Gäbler
Yvonne
Y
Kemmerling
Birgit
B
Haapalainen
Minna-Liisa
ML
Li
Chun-Mei
CM
Wei
Zhongmin
Z
Keller
Harald
H
Joosten
Matthieu
M
Taira
Suvi
S
Nürnberger
Thorsten
T
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D007113:Immunity, Innate; D008081:Liposomes / Q000378:metabolism; D016254:Mutagenesis, Insertional; D028528:Petroselinum / Q000276:immunology / Q000382:microbiology*; D010935:Plant Diseases / Q000382:microbiology*; D044224:Pseudomonas syringae / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D008081:Liposomes; D011994:Recombinant Proteins; D037521:Virulence Factors