A novel tetratricopeptide repeat-containing J-protein localized in a plasma membrane-bound protein complex of the phytopathogenic oomycete Phytophthora megasperma

Phytoalexins originating from plant tissues may cause within cells of fungi or oomycetes a change in the localization of actin, tubulin and chaperones . To test the hypothesis in a filamentously growing oomycete, we compared t he distribution of cellular markers in the presence and absence of hydroxys tilbene phytoalexins. Using cDNA from the phytopathogenic organism Phytopht hora megasperma, the causal agent of root rot on soybean and many other pla nts, and including probes for Hsp70 and Hsp40, we cloned a DnaJ-protein (Jc p) with the capacity of interacting with both a particular Hsp70 isoform vi a its J-domain and with other proteins via its tetratricopeptide, repeat (T PR) domain. Antisera raised against the bacterially expressed protein Jcp a llowed the analysis of its intracellular localization during hyphal growth. Following the subfractionation of cell homogenates, we detected virtually all immunoreactive Jcp in the plasma membrane-enriched fraction and as cons tituent of a membrane-associated protein complex. In agreement with the bio chemical findings, immunocytochemical stains of hyphae showed Jcp as part o f cortical patches positioned along the plasma membrane similar to the dist ribution of actin patches. Confocal microscopy, however, revealed that the Jcp-containing patches did not generally co-localize with the patches visua lized by the actin stain. The 59-kDa Jcp, characterized by a large 8-fold T PR domain at the N-terminal region and a J-domain close to the C-terminus, is a good candidate for bridging the gap between Hsp70 and Usp90 by protein -protein interactions. By administration of plant-derived phytoalexins it w as shown that the presence of resveratrol or piceatannol significantly redu ces the amount of the Jcp-containing patches, but does not lead to a reloca lization of intracellular Jcp.