Transcriptome Comparisons Identify Candidate Verticillium Wilt Resistance Genes in Mint (Mentha spp.)

Mentha species are cultivated for their essential oils, which provide important chemical components in a variety of consumer products. The most prevalent peppermint cultivar, Black Mitcham, is highly susceptible to Verticilium wilt, a disease caused by the oomycete fungus Verticillium dahliae Kleb. Development of Verticillium-resistant cultivars is complicated by polyploidy and sterility of commercial cultivars. Traditional breeding of mint can be achieved with diploid, fertile ancestral mint species. However, to achieve this goal, it is imperative to uncover the underlying genetic determinants of resistance and susceptibility. This project aims to develop genome resources and identify genes involved in the mint-Verticillium interaction as well as ones that are expressed differently in resistant mints relative to susceptible ones. In this study, we analyzed gene expression of two susceptible and two resistant cultivars: wilt-susceptible Black Mitcham peppermint and wilt-resistant Native spearmint, and two wild, diploid Mentha longifolia accessions from South Africa: wilt-resistant CMEN 585 and wilt-susceptible CMEN 584. Differential gene expression was examined between Verticillium-inoculated and mock-inoculated plants 10 and 20 days post inoculation (dpi) in roots and stems. In both resistant and susceptible mints, greater numbers of genes were differentially regulated in stems than in roots. Greater numbers of genes were differentially regulated in inoculated roots relative to controls at 20 dpi (225-705) than at 10 dpi (72-145). Few of the differentially-regulated genes were in common between resistant and susceptible mints. This work has identified a set of candidate genes for wilt resistance in mint.