The Pseudomonas AvrPto Protein Is Differentially Recognized by Tomato and Tobacco and Is Localized to the Plant Plasma Membrane

Abstract

The avrPto gene of Pseudomonas syringae pv tomato triggers race-specific resistance in tomato plants carrying Pto , a resistance gene encoding a protein kinase. When introduced into P. s. tabaci , avrPto triggers resistance in tobacco W38 plants that carry the corresponding R gene. The AvrPto protein is believed to be secreted into host cells through the bacterial type III secretion pathway, where it activates disease resistance in tomato by interacting with Pto. We report here the identification of two distinct regions in AvrPto that determine the recognition specificity of this protein in tomato and tobacco. Point mutations in the central region disrupted the avirulence activity in tomato but not in tobacco. Conversely, point mutations in the C-terminal region abolished the avirulence in tobacco but not in tomato. We further report that AvrPto was localized to the plasma membrane of plant cells. Disrupting the membrane association by mutating a putative myristoylation motif of AvrPto abolished the avirulence activity in both tomato and tobacco. These findings demonstrate that AvrPto is recognized differently by the R genes in tomato and tobacco and that the recognition of AvrPto probably is associated with the plasma membrane. INTRODUCTIONAvirulence ( avr ) genes trigger gene-for-gene resistance in plants containing the corresponding disease resistance ( R ) genes . Numerous avr genes have been cloned from various bacterial pathogens. Recent studies suggest that bacterial Avr proteins are secreted into the host cells through the type III secretion pathway and subsequently are perceived by the corresponding R gene products (reviewed in Alfano and Collmer, 1997;Lindgren, 1997;He, 1998;Kjemtrup et al., 2000).The AvrBs3 protein represents one family of bacterial Avr proteins that share high sequence similarities. These proteins contain a variable number of nearly identical repeat domains in the internal portion of the protein (Leach and White, 1996). Deletion and mutagenesis analysis indicate that the internal repeat region determines the recognition specificity of the AvrBs3 protein (Herbers et al., 1992). AvrBs3 -like proteins contain a nuclear localization sequence and have been detected in plant nuclei (Yang and Gabriel, 1995;Van den Ackerveken et al., 1996;Zhu et al., 1998 Zhu et al., , 1999. The transcription activity of AvrXa10, a member of the AvrBs3 family, in eukaryotic cells is essential for its avirulence function (Zhu et al., 1999). The AvrBs3-like proteins may mediate the avirulence function by regulating plant gene expression.Other bacterial Avr proteins do not carry a characteristic sequence indicative of recognition specificity and in planta localization (Leach and White, 1996). The reciprocal interchanges between AvrB and AvrC, two Avr proteins that share considerable sequence similarity, have identified a large central region in AvrB and AvrC that determines the recognition specificity (Tamaki et al., 1991). The rest of the bacterial Avr proteins do not share much homology with each other or w...

The Tomato Kinome and the Tomato Kinase Library ORFeome: Novel Resources for the Study of Kinases and Signal Transduction in Tomato and Solanaceae Species

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Functional domains and motifs of bacterial type III effector proteins and their roles in infection

“…All bacterial effectors that have defined Myr and Palm sites are from plant pathogens, particularly P. syringae, and include the HopZ family, HopF2 (Lewis et al, 2008), AvrPhB, AvrRpm1, AvrB, AvrC, AvrPto (Nimchuk et al, 2000;Shan et al, 2000;Maurer-Stroh & Eisenhaber, 2004;Robert-Seilaniantz et al, 2006) and Xanthomonas XopE1/2 (Thieme et al, 2007). Almost all these effectors encode a Myr motif at their extreme N-terminus that targets them to the plant plasma membrane.…”

Suppression of the MicroRNA Pathway by Bacterial Effector Proteins

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