Subcellular localization and functional analyses of a PR10 protein gene from Vitis pseudoreticulata in response to Plasmopara viticola infection.

Downy mildew, caused by the oomycete Plasmopara viticola, is a serious fungal disease in the cultivated European grapevines (Vitis vinifera L.). The class 10 of pathogenesis-related (PR) genes in grapevine leaves was reported to be accumulated at mRNA level in response to P. viticola infection. To elucidate the functional roles of PR10 genes during plant-pathogen interactions, a PR10 gene from a fungal-resistant accession of Chinese wild Vitis pseudoreticulata (designated VpPR10.2) was isolated and showed high homology to PR10.2 from susceptible V. vinifera (designated VvPR10.2). Comparative analysis displayed that there were significant differences in the patterns of gene expression between the PR10 genes from the two host species. VpPR10.2 was induced with high level in leaves infected by P. viticola, while VvPR10.2 showed a low response to this inoculation. Recombinant VpPR10.2 protein showed DNase activity against host genomic DNA and RNase activity against yeast total RNA in vitro. Meanwhile, recombinant VpPR10.2 protein inhibited the growth of tobacco fungus Alternaria alternata and over-expression of VpPR10.2 in susceptible V. vinifera enhanced the host resistance to P. viticola. The results from subcellular localization analysis showed that VpPR10.2 proteins were distributed dynamically inside or outside of host cell. Moreover, they were found in haustorium of P. viticola and nucleus of host cell which was associated with a nucleus collapse at 10 days post-inoculation. Taken together, these results suggested that VpPR10.2 might play an important role in host plant defense against P. viticola infection.