Plant viruses and viroids are minimal pathogens and depend upon interaction with key host components during pathogenesis. The temporal and spatial regulation off host factors during initial host-pathogen interactions is conditioned by host recognition of viral/viroid signals and the subsequent transduction of the signal leading to metabolic alterations. The processes by which these agents manipulate host plant proteins are unknown. Protein phosphorylation-dephosphorylation cascades are important post- translational processes which serve to rapidly amplify and transduce specific developmental and environmental signals and coordinate metabolic responses. This laboratory has characterized a plant-encoded protein kinase (p68) whose autophosphorylation is induced in viral and viroid infected plants and in noninfected tissue extracts supplemented with viral dsRNA and artificial dsRNA. The response is signal dependent and occurs in the initial phases of pathogenesis. Studies to date have emphasized biochemical and immunological characterization of p68. In order to better understand the role of p68 it is necessary to begin analysis at the gene level. The investigator has chosen to use both virus- and viroid-host models. Each has distinct attributes. This project will further characterize the significance of p68 activity in host- pathogen interactions and in healthy plants by isolating, sequencing and studying the cDNA and genomic clones of p68. The functional significance also may be indicated by determining the phosphorylation of p68 in tissues challenged with viroid mutants which vary in both RNA stability and pathogenicity. The role of p68 may also be indicated by expression of sense and antisense constructs in transgenic plants. p68 appears to be the only plant protein thus far described that is associated with dsRNA dependent protein kinase activity. The viral/viroid-plant systems are excellent models to define the significance of phosphorylation in host-pathogen interactions as well as to study the role of phosphorylation in healthy plants and how that function is altered during infection. %%% Addition or removal of phosphate groups (phosphorylation, dephosphorylation) from specific proteins plays an important role in the recognition and amplification of environmental and biological signals in all organisms. This process may also have a central role in the way plants perceive and respond to signals generated during attack by pathogens or wounding. The goal of this research is to determine the role of protein phosphorylation in virus-plant interactions. It will focus on a specific protein, "p68", that catalyzes the addition of phosphate to itself in the presence of double stranded RNA from plant viruses. The role of p68 in normal plant physiology and during viral infection will be studied. The processes by which viruses manipulate normal proteins after they infect plants are largely unknown. The results of this research should be an important contribution to basic understanding of how plants respond to viruses.
