Invasion of host plants by the bean rust fungus, Uromyces appendiculatus , occurs through stomata and requires the development of infection structures, e.g. appressoria. Appressorium formation is a cell differentiation event that occurs in response to contact (thigmotropic) stimuli. Cell differentiation begins with the onset of nuclear division. Evidence that at least fifteen species of protein are synthesized when germlings are induced to differentiate, has led to the study of the nature of the genes which are activated and the nature and role of the proteins. During the previous granting period four genes have been isolated that are specifically expressed by the time differentiation is complete. Dr. Staples will now analyze the dr.genes in terms of detailed structures, the time in the differentiation process when they are first expressed, their homology with DNA from other fungi, and an identification of their gene products. He will prepare antibodies specific for these protein gene products and use them to determine the location in the germling of the dr.proteins. In addition attempts will be made to isolate differentiation related genes that are expressed earlier than 6 h in the differentiation process, i.e. before differentiation is complete. The studies will significantly advance our knowledge of the mechanisms involved in the fungal sensing responses that result in the accurate placement of the appressorium over the stomate during host colonization.
