9303359 Martin The long term objective of this research is to elucidate the function of plant disease resistance (DR) genes. The interaction of tomato and the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) provides an ideal system for understanding gene-for- gene complementarity. Resistance to Pst in tomato is conferred by a single, mapped locus, Pto and an avr gene corresponding to Pto has been isolated (avrPto). A multi-step positional cloning strategy has recently been used to identify a yeast artificial chromosome (YAC) clone that contains the Pto locus. We now propose to molecularly isolate the Pto locus from this YAC clone and characterize its role in resistance. We will isolate the Pto bacterial resistance locus; determine the DNA sequence of Pto and examine its structural features; investigate potential alternate alleles of Pto that exist in susceptible plants; characterize the spatial and temporal expression patterns of the Pto gene; examine the expression patterns of pathogenesis-related (PR) genes and other defense-related using Pto isogenic lines, and determine the spatial and temporal accumulation patterns of the Pto protein. %%% Knowledge of the DNA sequence of the Pto gene and the localization of its gene product in the plant cell will address fundamental questions in cell-cell interactions. In addition, since the Pto gene will likely be one of the first plant resistance genes isolated, its characterization may facilitate the isolation of disease resistance genes from other plant species. ***
