Identification of Resistance Gene Analogs and Verticillium Wilt Resistance-like Sequences in Mentha longifolia

Abstract

Resistance gene analog (RGA) sequences were obtained from four Mentha longifolia (L.) Huds. accessions using degenerate polymerase chain reaction (PCR) primers targeting the conserved nucleotide binding site domain found in many plant disease resistance genes. Seven distinct RGA families were identified. All M. longifolia RGAs showed similarity to sequences of the non-toll-interleukin 1 receptor R gene class. In addition, degenerate PCR primers based on the tomato (Solanum lycopersicum L.) verticillium wilt resistance (Ve) genes were used to PCR-amplify a 445-base pair (bp) Ve-like sequence from M. longifolia that had ≈57% predicted amino acid identity with Ve. Mint-specific primers based on the original mint Ve sequence were used to obtain mint-specific Ve sequences from four M. longifolia accessions and from peppermint (Mentha ×piperita L.) cultivar ‘Black Mitcham’ that had 95% to 100% predicted amino acid identity to the original mint Ve sequence. Inverse PCR was then used to obtain flanking mint Ve sequence from one M. longifolia accession extending the mint Ve sequence to 1077 bp. This is the first report of RGA sequences in the Lamiaceae and the first report of Ve-like sequences obtained with degenerate PCR primers.