Abstract
Mentha longifolia is a wild mint species being used as a model to study the genetics of resistance to the fungal wilt pathogen Verticillium dahliae. We used high-throughput Illumina sequencing to study gene expression in response to V. dahliae inoculation in two M. longifolia USDA accessions with contrasting phenotypes: wilt-resistant CMEN 585 and wilt-susceptible CMEN 584. Roots and stems were sampled at two early post-inoculation time points, four hours and twenty-four hours, and again at ten days and twenty days post-inoculation. Overall, many more genes were differentially-regulated in wilt-resistant CMEN 585 than in wilt-susceptible CMEN 584. The greatest numbers of differentially expressed genes were found in the roots of CMEN 585 at the early time points. Specific genes exhibiting early, strong upregulation in roots of CMEN 585 but not in CMEN 584 included homologs of known plant defense response genes as well as genes involved in monoterpene biosynthesis. These genes were also upregulated in stems at the later time points. This study provides a comprehensive view of transcription reprogramming in Verticillium wilt-resistant mint, which will be the basis for further study and for molecular marker development.
Highlights
Vascular wilt disease caused by the soil-borne deuteromycete fungus Verticillium dahliae is a devastating disease of commercial peppermint (Mentha × piperita)
We present a comprehensive profile of gene expression in roots and stems of two South African M. longifolia accessions representing extremes of Verticillium wilt resistance vs. susceptibility
Transcriptome sequencing was done on RNA samples isolated from roots and stems of either water- or V. dahliae spore-inoculated CMEN 585 and CMEN 584 plants
Summary
Vascular wilt disease caused by the soil-borne deuteromycete fungus Verticillium dahliae is a devastating disease of commercial peppermint (Mentha × piperita). The fungus invades through the root system and proliferates in the xylem. Symptoms of Vertcillium wilt disease in mint range from mild chlorosis and “crescent leaf” (Figure 1) to wilting and death of plants. V. dahliae is a widespread plant pathogen, affecting annuals, perennials, and woody plants. Verticillium wilt disease has been studied in many different crops, including cotton, lettuce, and the Solanaceae [1–8]. Genetic resistance to Verticillium wilt was first mapped in tomato, and two linked genes at the mapped locus, Ve1 and Ve2, were cloned in 2001 [9,10]. Ve1 but not Ve2 was shown to confer resistance to tomato Verticillium wilt. Subsequent studies identified positive regulators of Ve1 as well as downstream signaling components in the Ve1mediated pathway
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