Cloning and characterization of the PtVIP1 gene in Populus

The VirE2-interaction protein 1 (VIP1) serves as a regulator of mitogen-activated protein kinase 3 (MPK3)-mediated stress gene modulation under biotic stress, which in turn activates the MPK3 pathway in Arabidopsis . The mode of action of the VIP1 protein in Populus in response to biotic stress remains unknown. In this study, we cloned the full-length cDNA of the PtVIP1 gene from Populus trichocarpa (accession number of GenBank: KY793105). The VIP1 protein harboured a conserved bZIP (basic leucine zipper) domain located in the C-terminus. The VIP1 subcellular localization assay indicated that the VIP1 protein was present in the cytoplasm and nucleus under normal conditions, and that an increase in the amount of the protein in the nucleus occurred after treatment with flg22, the elicitor-active epitope of flagellin which triggers the innate immune response in plants. Transgenic Populus plants overexpressing VIP1 genes ( PtVIP1 of Populus ; or AtVIP1 of Arabidopsis , as positive control) were generated to investigate the role of VIP1 in vivo. The expression of poplar pathogenesis-related protein 1 ( PR1 ) genes was up-regulated in transgenic- PtVIP1 or AtVIP1 poplar plants. The transgenic poplar plants overexpressing PtVIP1 or AtVIP1 also showed enhanced resistance to Brenneria salicis infection. These results suggest that the VIP1 protein accumulates in the nucleus in response to biotic stress, and that the pathogen resistance of transgenic VIP1 poplar may be associated with the induced expression of PR1 genes in response to pathogen challenge.