Pathogen recognition and signal transduction by the tomato Pto kinase
Abstract
The Pto disease resistance (R) gene was previously identified in the wild tomato species Lycopersicon pimpinellifolium. Pto encodes a serine-threonine protein kinase that recognizes strains of Pseudomonas syringae pv. tomato (Pst) expressing the avirulence gene avrPto. To determine the degree of conservation among Pto orthologs, we examined an accession of the distantly related wild species L. hirsutum var. glabratum that also exhibits avrPto-specific resistance to Pst. Previous observations suggested that a member of an orthologous Pto gene family confers Pst(avrPto) resistance in this L. hirsutum line. Here we report the cloning and characterization of four members of the Pto family from L. hirsutum. One gene (LhirPto) is 97% identical to Pto and encodes a catalytically active protein kinase that elicits a hypersensitive response when co-expressed with avrPto in leaves of Nicotiana benthamiana. In common with the Pto kinase, the LhirPto protein physically interacts with AvrPto and downstream members of the Pto signaling pathway. Our studies indicate that avrPto recognition specificity evolved prior to the divergence of L. hirsutum from L. pimpinellifolium. Pto mediates disease resistance following a physical interaction with the bacterial effector proteins AvrPto and AvrPto2. Where this interaction occurs and how it activates the plant defense response is currently unknown. To develop a system in which we can observe this process in vivo, we integrated the green florescent protein into the Agrobacterium mediated transient assay that is commonly used to investigate gene for gene interactions. Our approach allows the concurrent investigation of protein function and protein localization in planta. Here we report results describing the localization of Pto, AvrPto, and AvrPto2. Our findings support previous observations that Pto need not reside at the plasma membrane to effect a disease resistance response and may in fact function both at the plasma membrane and in the cytosol. Additional applications of this technique can potentially prove valuable for elucidating the molecular mechanism of Pto mediated disease resistance.
Degree
Ph.D.
Advisors
Martin, Purdue University.
Subject Area
Molecular biology|Agronomy
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