Functional mapping of harpin HrpZ of Pseudomonas syringae reveals the sites responsible for protein oligomerization, lipid interactions and plant defence induction

Minna Liisa Haapalainen, Stefan Engelhardt, Isabel Kufner, Chun Mei Li, Thorsten Nurnberger, Justin Lee, Martin Romantschuk, Suvi Taira

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Harpin HrpZ is one of the most abundant proteins secreted
through the pathogenesis-associated type III secretion system
of the plant pathogen Pseudomonas syringae. HrpZ shows
membrane-binding and pore-forming activities in vitro, suggesting
that it could be targeted to the host cell plasma membrane.
We studied the native molecular forms of HrpZ and found that it
forms dimers and higher order oligomers. Lipid binding by HrpZ
was tested with 15 different membrane lipids, with HrpZ interacting
only with phosphatidic acid. Pore formation by HrpZ in
artificial lipid vesicles was found to be dependent on the presence
of phosphatidic acid. In addition, HrpZ was able to form
pores in vesicles prepared from Arabidopsis thaliana plasma
membrane, providing evidence for the suggested target of HrpZ
in the host. To map the functions associated with HrpZ, we
constructed a comprehensive series of deletions in the hrpZ gene
derived from P. syringae pv. phaseolicola, and studied the
mutant proteins.We found that oligomerization is mainly mediated
by a region near the C-terminus of the protein, and that the
same region is also essential for membrane pore formation.
Phosphatidic acid binding seems to be mediated by two regions
separate in the primary structure. Tobacco, a nonhost plant,
recognizes, as a defence elicitor, a 24-amino-acid HrpZ fragment
which resides in the region indispensable for the oligomerization
and pore formation functions of HrpZ.
Original languageEnglish
JournalMolecular Plant Pathology
Volume12
Issue number2
Pages (from-to)151-166
Number of pages16
ISSN1464-6722
DOIs
Publication statusPublished - 2011
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 1181 Ecology, evolutionary biology
  • 1182 Biochemistry, cell and molecular biology
  • 1183 Plant biology, microbiology, virology
  • 1184 Genetics, developmental biology, physiology

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