Isolation of resistance gene analogs from grapevine resistant to downy mildew

Downy mildew caused by Plasmopara viticola is a devastating disease that results in considerable economic losses as well as environmental damage through the repeated application of fungicides in cultivated grapevine (Vitis spp.). In this study, degenerate primers that were designed based on the conserved motifs in the NBS domain of resistance proteins were used to isolate NBS-type sequences. A total of 10 RGA fragments were identified, and their predicted amino acid sequences compared to each other and to the amino acid sequences of known R-genes revealed significant sequence similarity. Phylogenetic analysis demonstrated that 10 RGAs dispersed along the phylogram on the two major branches of either TIR or non-TIR type of the NBS-LRR proteins. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that transcripts of RGA1, RGA2, RGA5 and RGA23 were specifically induced after infection with P. viticola. These results suggest that RGA1, RGA2, RGA5 and RGA23 may play roles in defense mechanisms that confer resistance to downy mildew in grapevine.

► RGAs against downy mildew were searched for in mRNA from infected grapevine.
► Ten RGA fragments had characteristics typical of nucleotide binding site domains.
► RGA1, RGA2, RGA5 and RGA23 were induced specifically after infection with P. viticola.
► RGA1, RGA2, RGA5 and RGA23 may play roles in defense against downy mildew in grapevine.