Draft Genome Sequence of Mentha longifolia and Development of Resources for Mint Cultivar Improvement

Abstract

The genus Mentha encompasses mint species cultivated for their essential oils, which are formulated into a vast array of consumer products. Desirable oil characteristics and resistance to the fungal disease Verticillium wilt are top priorities for the mint industry. However, cultivated mints have complex polyploid genomes and are sterile. Breeding efforts, therefore, require the development of genomic resources for fertile mint species. Here, we present draft de novo genome and plastome assemblies for a wilt-resistant South African accession of Mentha longifolia (L.) Huds., a diploid species ancestral to cultivated peppermint and spearmint. The 353 Mb genome contains 35 597 predicted protein-coding genes, including 292 disease resistance gene homologs, and nine genes determining essential oil characteristics. A genetic linkage map ordered 1397 genome scaffolds on 12 pseudochromosomes. More than two million simple sequence repeats were identified, which will facilitate molecular marker development. The M. longifolia genome is a valuable resource for both metabolic engineering and molecular breeding. This is exemplified by employing the genome sequence to clone and functionally characterize the promoters in a peppermint cultivar, and demonstrating the utility of a glandular trichome-specific promoter to increase expression of a biosynthetic gene, thereby modulating essential oil composition.

Plant Glandular Trichomes: Natural Cell Factories of High Biotechnological Interest

“…The (draft) genome sequences of a number of plant species with glandular trichomes are now available. A nonexhaustive list includes different tomato species (Solanum lycopersicum and Solanum pimpinellifolium [Tomato Genome Consortium, 2012] and Solanum pennellii [Bolger et al, 2014]), potato (Solanum tuberosum [Xu et al, 2011]), cucumber (Cucumis sativus [Huang et al, 2009]), tobacco (Nicotiana tabacum [Sierro et al, 2014;Edwards et al, 2017]) and its related species (Nicotiana sylvestris and Nicotiana tomentosiformis [Sierro et al, 2013]), hot pepper (Capsicum annuum ), mint (Mentha longifolia [Vining et al, 2017]), cannabis (Cannabis sativa [van Bakel et al, 2011]), and hop (Humulus lupulus [Natsume et al, 2015]). …”

Bioenergetics of Monoterpenoid Essential Oil Biosynthesis in Nonphotosynthetic Glandular Trichomes

“…The hybrid hexaploid nature of peppermint makes it difficult to answer this question due to the potential for the presence of many Fd isoforms in genomes retained from three different ancestral species. However, the recently completed draft genome assembly for M. longifolia, a diploid species related to one of the ancestors of presentday peppermint (Vining et al, 2017), allowed us to examine all Fd isoforms. Organ-and tissue-specific transcriptome data for M. longifolia were recently deposited in public archives (root and GT transcriptomes with National Center for Biotechnology Information [NCBI] short read archive accession nos.…”

“…Protocols for the Agrobacterium tumefaciens-mediated transformation of mint species had been developed in the late 1990s (Berry et al, 1996;Caissard et al, 1996;Diemer et al, 1998;Niu et al, 1998) and were later employed, supported in part by mathematical modeling, to successfully modulate monoterpenoid essential composition and yield in transgenic peppermint plants (Mahmoud and Croteau, 2001; Mahmoud et al, 2004;Lange et al, 2011. The draft genome sequence and genetic map of Mentha longifolia, a diploid mint related to the ancestors of present-day peppermint and spearmint (Mentha 3 spicata; which are both polyploid), are resources that now also enable advanced breeding approaches for cultivar improvement (Vining et al, 2017).…”

Is It Ordered Correctly? Validating Genome Assemblies by Optical Mapping

“…Indeed, the sequencing and assembly methods required to achieve a high level of contiguity are well within reach of many laboratories, including those working with trees (Neale et al, 2014), minor crops (Clouse et al, 2016;Jarvis et al, 2017), or ecological systems (Martínez-García et al, 2016;Olsen et al, 2016;Tang et al, 2016;Vining et al, 2017). If a research group invests in mate-pair or long-read sequencing at high depth, it is natural to proceed to genome assembly, even though the assembly may never be used for map-based cloning or genetic analysis in the traditional sense.…”