The VvHMGA protein acts as a putative positive regulator of VvLOR9 in grapevine resistance to downy mildew

The late upregulated in response to Hyaloperonospora parasitica (LURP)-one-related (LOR) gene family is critical for defense against oomycete pathogens, yet its transcriptional regulatory mechanisms remain largely unexplored. In this study, a genome-wide analysis identified a total of 12 Vitis vinifera LOR (VvLOR) genes in grapevine, which were unevenly distributed across five chromosomes. Notably, motif 2, characterized by the conserved sequence YDYRIZGSYSKRSCKIYBS, was highly conserved among the 12 members. Phylogenetic analysis assigned VvLOR9 to a defense-related clade that also contains Arabidopsis thaliana LURP1 (AtLURP1) and LOR1 (AtLOR1) . Promoter analysis revealed multiple AT-rich TATA-box motifs within the VvLOR9 promoter. Using yeast one-hybrid screening, we identified Vitis vinifera high mobility group A (VvHMGA) as an upstream regulator of VvLOR9 . Expression analysis showed that VvLOR9 is a delayed-upregulated gene in response to Plasmopara viticola infection, and VvHMGA exhibited a similar expression pattern during the late infection stages (60–120 h postinfection). Electrophoretic mobility shift assays (EMSA) and dual-luciferase reporter assays demonstrated that VvHMGA directly binds to the AT-TATA-box motifs in the VvLOR9 promoter and positively activates its transcription. Furthermore, transient overexpression of either VvLOR9 or VvHMGA in grapevine significantly enhanced resistance to P. viticola . Collectively, our findings uncover a novel putative regulatory module in which VvLOR9 , positively regulated by VvHMGA, confers resistance to grapevine downy mildew.