Role of the Hrp Pilus in Type III Protein Secretion in Pseudomonas syringae

Abstract

Bacterial surface appendages called pili and needle-like filaments are associated with protein and/or DNA transfer to recipient plant, human, or bacterial cells during pathogenesis or conjugation. Although it has long been suspected that pili function as a conduit for protein or DNA transfer, direct evidence has been lacking. The Hrp pilus of Pseudomonas syringae is assembled by the type III secretion system. We used an in situ immunogold labeling procedure to visualize the extrusion of an effector protein, AvrPto, from the tip of the Hrp pilus, providing direct evidence that a bacterial pilus can function as a conduit for protein delivery.

Dissection of homologous translocon operons reveals a distinct role for YopD in type III secretion by Yersinia pseudotuberculosis

“…The bacterial envelope component of the TTSSs of many plant-and animal-interacting bacteria resembles the flagella basal body, while a hollow needle-like protrusion extends from the bacterial surface through which effectors are believed to traverse (Blocker et al, 1999;Hoiczyk & Blobel, 2001;Jin & He, 2001;Kubori et al, 1998;Sekiya et al, 2001;Tamano et al, 2000). Furthermore, translocation into target cells by Yersinia requires the structural proteins LcrV, YopB and YopD.…”

“…This specialized virulence strategy links protein secretion across the bacterial envelope with translocation of anti-host virulence effectors through the plasma membrane of target eukaryotic cells. Effector proteins localized inside the target cell disable crucial signal transduction pathways, rendering the cell incapable of mounting an effective immune defence (Bliska, 2000; Fällman et al, 2002).The bacterial envelope component of the TTSSs of many plant-and animal-interacting bacteria resembles the flagella basal body, while a hollow needle-like protrusion extends from the bacterial surface through which effectors are believed to traverse (Blocker et al, 1999;Hoiczyk & Blobel, 2001;Jin & He, 2001;Kubori et al, 1998; Sekiya et al, 2001;Tamano et al, 2000). Furthermore, translocation into target cells by Yersinia requires the structural proteins LcrV, YopB and YopD.…”

Molecular Evolution of Pathogenicity-Island Genes in Pseudomonas viridiflava

“…hrpA, hrpZ, and hrpW encode outer proteins involved in the type-III secretion system (TTSS). hrpA encodes the pilus, which plays a key role in the secretion of Avr and other type-III effector proteins and is subject to natural selection in P. syringae ( Jin and He 2001;Guttman et al 2006). hrpZ and hrpW encode harpin proteins Preston et al 1995), which also elicit HR in the apoplast (in contrast to Avr proteins that elicit HR in plant cells; Wei et al 1992;He et al 1993).…”

Structure of HrcQ B -C, a conserved component of the bacterial type III secretion systems

“…The Hrp system consists of a secretion apparatus encoded by Ϸ25 hrp genes and its main function is to deliver virulence proteins (effectors) into plant cells (5)(6)(7). A broadly conserved subset of the hrp genes (designated hrc) appears to encode the core components of the delivery apparatus (2).…”