Understanding the molecular basis of disease-resistance genes has long been a goal of plant pathology. With the advent of gene cloning technology in the 1970s, this goal finally became realistic and in the intervening years several important host defense-related genes have been cloned and characterized. 1 - 4 Nevertheless, the goal of cloning actual resistance genes, as opposed to host response genes, has remained elusive. For the most part, this is because most, if not all, disease-resistance genes are defined genetically through segregation analysis and transmission genetics. By contrast, current gene cloning techniques depend upon some biochemical connection to the gene, generally through the protein or mRNA product to isolate the gene. This explains why so many host response genes-and so few plant disease-resistance genes-have been cloned to date.