Molecular characterization of the interactions between tomato and Pseudomonas syrinagae pv. tomato.

摘要

Pto of tomato confers gene-for-gene resistance to Pseudomonas syringae pv. tomato expressing avrPto. Mutagenesis of avrPto was conducted to further characterize its interaction with Pto. Analysis of deletion mutants indicated a central region of 95 residues was sufficient for interactions with Pto in the yeast two-hybrid system. Analysis of substitution mutants suggested AvrPto can tolerate many alterations; only a few substitutions affected its interaction with Pto. The ability to elicit a HR in planta and the effects each avrPto mutant had on pathogenesis of tobacco by P. syringae pv. tabaci strongly correlated with interactions with Pto. Substitutions of some residues within AvrPto affected its stability in the cytoplasm of P. syringae and its delivery by the pathogen.; P. syringae pv. tomato expressing avrPto caused enhanced necrosis on tomato lines lacking functional Pto or Prf genes relative to symptoms caused by strains lacking avrPto. Enhanced necrosis correlated with increased bacterial replication at 4 dpi. Necrosis was more severe in plants lacking Prf when compared to plants lacking Pto. Transient expression of avrPto resulted in non-confluent HR in tomato lines lacking Pto but not Prf. Therefore, a minor recognition determinant of AvrPto may be encoded at the Pto locus. Additionally, AvrPto is either not directly causing or requires other molecules for causing enhanced necrosis.; Homologs of Pto are present in the Pto locus of the resistance line Rio Grande 76R, as well as that of the susceptible lines Rio Grande 76S and VFNT Cherry. To determine whether the Pto homologs could function as resistance proteins or as the minor recognition determinant of AvrPto, each was characterized for function. Except for Pto, no interactions with AvrPto were detected in the yeast two-hybrid system. In addition to the other Pto homologs with reported autophosphorylation activity, escPth2 autophosphorylated in vitro. Substitutions were introduced into the P+1 loop of the Pto homologs to generate mutants that could potentially elicit constitutive, ligand-independent cell death. Three homologs from the susceptible haplotype carrying substitutions in their P+1 loop and two wild-type homologs of Pto from the resistant haplotype elicited cell death. Therefore, several of the Pto homologs may encode functional resistance proteins.