THE MAIZE PATHOGENESIS-RELATED PRMS PROTEIN LOCALIZES TO PLASMODESMATA IN MAIZE RADICLES

Pathogenesis-related (PR) proteins are plant proteins induced in respo nse to infection by pathogens. In this study, an antibody raised again st the maize PRms protein was used to localize the protein in fungal-i nfected maize radicles. The PRms protein was found to be localized at the contact areas between parenchyma cells of the differentiating prot oxylem elements. By using immunoelectron microscopy, we found that the se immunoreactive regions correspond to plasmodesmal regions. This was also true for the parenchyma cells filling the central pith of the va scular cylinder, although PRms mRNA accumulation was not detected in t hese cells. These findings suggest that for one cell type, the parench yma cells of the central pith, the protein is imported rather than syn thesized. The localization of the PRms protein indicates the possible existence of mechanisms for sorting of plant proteins to plasmodesmata and suggests that this protein may have a specialized function in the plant defense response. These findings are discussed with respect to the structure and function of plasmodesmata in cell-to-cell communicat ion processes in higher plants.