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Mentha canadensis L. is an important spice crop and medicinal herb with high economic value. The plant is covered with peltate glandular trichomes, which are responsible for the biosynthesis and secretion of volatile oils. Plant non-specific lipid transfer proteins (nsLTPs) belong to a complex multigenic family involved in various plant physiological processes. Here, we cloned and identified a nonspecific lipid transfer protein gene (McLTPII.9) from M. canadensis, which may positively regulate peltate glandular trichome density and monoterpene metabolism. McLTPII.9 was expressed in most M. canadensis tissues. The GUS signal driven by the McLTPII.9 promoter in transgenic Nicotiana tabacum was observed in stems, leaves, and roots; it was also expressed in trichomes. McLTPII.9 was associated with the plasma membrane. Overexpression of McLTPII.9 in peppermint (Mentha piperita. L) significantly increased the peltate glandular trichome density and total volatile compound content compared with wild-type peppermint; it also altered the volatile oil composition. In McLTPII.9-overexpressing (OE) peppermint, the expression levels of several monoterpenoid synthase genes and glandular trichome development-related transcription factors--such as limonene synthase (LS), limonene-3-hydroxylase (L3OH), geranyl diphosphate synthase (GPPS), HD-ZIP3, and MIXTA--exhibited varying degrees of alteration. McLTPII.9 overexpression resulted in both a change in expression of genes for terpenoid biosynthetic pathways which corresponded with an altered terpenoid profile in OE plants. In addition, peltate glandular trichome density was altered in the OE plants as well as the expression of genes for transcription factors that were shown to be involved in trichome development in plants. [ABSTRACT FROM AUTHOR]

Above-ground material of members of the mint family is commercially distilled to extract essential oils, which are then formulated into a myriad of consumer products. Most of the research aimed at characterizing the processes involved in the formation of terpenoid oil constituents has focused on leaves. We now demonstrate, by investigating three mint species, peppermint (Mentha×piperita L.), spearmint (Mentha spicata L.) and horsemint (Mentha longifolia (L.) Huds.; accessions CMEN 585 and CMEN 584), that other organs - namely stems, rhizomes and roots - also emit volatiles and that the terpenoid volatile composition of these organs can vary substantially from that of leaves, supporting the notion that substantial, currently underappreciated, chemical diversity exists. Differences in volatile quantities released by plants whose roots had been dipped in a Verticillium dahliae-spore suspension (experimental) or dipped in water (controls) were evident: increases of some volatiles in the root headspace of mint species that are susceptible to Verticillium wilt disease (peppermint and M. longifolia CMEN 584) were detected, while the quantities of certain volatiles decreased in rhizomes of species that show resistance to the disease (spearmint and M. longifolia CMEN 585). To address the genetic and biochemical basis underlying chemical diversity, we took advantage of the newly sequenced M. longifolia CMEN 585 genome to identify candidate genes putatively coding for monoterpene synthases (MTSs), the enzymes that catalyze the first committed step in the biosynthesis of monoterpenoid volatiles. The functions of these genes were established by heterologous expression in Escherichia coli, purification of the corresponding recombinant proteins, and enzyme assays, thereby establishing the existence of MTSs with activities to convert a common substrate, geranyl diphosphate, to (+)-α-terpineol, 1,8-cineole, γ-terpinene, and (-)-bornyl diphosphate, but were not active with other potential substrates. In conjunction with previously described MTSs that catalyze the formation of (-)-β-pinene and (-)-limonene, the product profiles of the MTSs identified here can explain the generation of all major monoterpene skeletons represented in the volatiles released by different mint organs. [ABSTRACT FROM AUTHOR]

Above-ground material of members of the mint family is commercially distilled to extract essential oils, which are then formulated into a myriad of consumer products. Most of the research aimed at characterizing the processes involved in the formation of terpenoid oil constituents has focused on leaves. We now demonstrate, by investigating three mint species, peppermint (Mentha ˣ piperita L.), spearmint (Mentha spicata L.) and horsemint (Mentha longifolia (L.) Huds.; accessions CMEN 585 and CMEN 584), that other organs – namely stems, rhizomes and roots – also emit volatiles and that the terpenoid volatile composition of these organs can vary substantially from that of leaves, supporting the notion that substantial, currently underappreciated, chemical diversity exists. Differences in volatile quantities released by plants whose roots had been dipped in a Verticillium dahliae-spore suspension (experimental) or dipped in water (controls) were evident: increases of some volatiles in the root headspace of mint species that are susceptible to Verticillium wilt disease (peppermint and M. longifolia CMEN 584) were detected, while the quantities of certain volatiles decreased in rhizomes of species that show resistance to the disease (spearmint and M. longifolia CMEN 585). To address the genetic and biochemical basis underlying chemical diversity, we took advantage of the newly sequenced M. longifolia CMEN 585 genome to identify candidate genes putatively coding for monoterpene synthases (MTSs), the enzymes that catalyze the first committed step in the biosynthesis of monoterpenoid volatiles. The functions of these genes were established by heterologous expression in Escherichia coli, purification of the corresponding recombinant proteins, and enzyme assays, thereby establishing the existence of MTSs with activities to convert a common substrate, geranyl diphosphate, to (+)-α-terpineol, 1,8-cineole, γ-terpinene, and (–)-bornyl diphosphate, but were not active with other potential substrates. In conjunction with previously described MTSs that catalyze the formation of (–)-β-pinene and (–)-limonene, the product profiles of the MTSs identified here can explain the generation of all major monoterpene skeletons represented in the volatiles released by different mint organs.

In recent years, the study of aromatic plants has seen an increase, with great interest from industrial, academic, and pharmaceutical industries. Among plants attracting increased attention are the Mentha spp. (mint), members of the Lamiaceae family. Mint essential oils comprise a diverse class of molecules known as terpenoids/isoprenoids, organic chemicals that are among the most diverse class of naturally plant derived compounds. The terpenoid profile of several Mentha spp. is dominated by menthol, a cyclic monoterpene with some remarkable biological properties that make it useful in the pharmaceutical, medical, cosmetic, and cleaning product industries. As the global market for Mentha essential oils increases, the desire to improve oil composition and yield follows. The monoterpenoid biosynthesis pathway is well characterised so metabolic engineering attempts have been made to facilitate this improvement. This review focuses on the Mentha spp. and attempts at altering the carbon flux through the biosynthetic pathways to increase the yield and enhance the composition of the essential oil. This includes manipulation of endogenous and heterologous biosynthetic enzymes through overexpression and RNAi suppression. Genes involved in the MEP pathway, the menthol and carvone biosynthetic pathways and transcription factors known to affect secondary metabolism will be discussed along with non-metabolic engineering approaches including environmental factors and the use of plant growth regulators. [ABSTRACT FROM AUTHOR]

In recent years, the study of aromatic plants has seen an increase, with great interest from industrial, academic, and pharmaceutical industries. Among plants attracting increased attention are the Mentha spp. (mint), members of the Lamiaceae family. Mint essential oils comprise a diverse class of molecules known as terpenoids/isoprenoids, organic chemicals that are among the most diverse class of naturally plant derived compounds. The terpenoid profile of several Mentha spp. is dominated by menthol, a cyclic monoterpene with some remarkable biological properties that make it useful in the pharmaceutical, medical, cosmetic, and cleaning product industries. As the global market for Mentha essential oils increases, the desire to improve oil composition and yield follows. The monoterpenoid biosynthesis pathway is well characterised so metabolic engineering attempts have been made to facilitate this improvement. This review focuses on the Mentha spp. and attempts at altering the carbon flux through the biosynthetic pathways to increase the yield and enhance the composition of the essential oil. This includes manipulation of endogenous and heterologous biosynthetic enzymes through overexpression and RNAi suppression. Genes involved in the MEP pathway, the menthol and carvone biosynthetic pathways and transcription factors known to affect secondary metabolism will be discussed along with non-metabolic engineering approaches including environmental factors and the use of plant growth regulators.

The isoprenoids play important ecological and physiological roles in plants. They also have a tremendous impact on human lives as food additives, medicines, and industrial raw materials, among others. Though some isoprenoids are highly abundant in nature, plants produce many at extremely low levels. Glandular trichomes (GT), which cover the aerial parts of more than 25% of vascular plants, have been considered as natural biofactories for the mass production of rare industrially important isoprenoids. In several plant genera (e.g., Lavandula and Mentha), GTs produce and store large quantities of the low molecular weight isoprenoids, in particular mono- and sesquiterpenes, as essential oil constituents. Within each trichome, a group of secretory cells is specialized to strongly and specifically express isoprenoid biosynthetic genes, and to synthesize and deposit copious amounts of terpenoids into the trichome’s storage reservoir. Despite the abundance of certain metabolites in essential oils and defensive resins, plants, particularly those lacking glandular trichomes, accumulate small quantities of many of the biologically active and industrially important isoprenoids. Therefore, there is a pressing need for technologies to enable the mass production of such metabolites, and to help meet the ever-increasing demand for plant-based bioproducts, including medicines and renewable materials. Considerable contemporary research has focused on engineering isoprenoid metabolism in GTs, with the goal of utilizing them as natural biofactories for the production of valuable phytochemicals. In this review, we summarize recent advances related to the engineering of isoprenoid biosynthetic pathways in glandular trichomes.

The isoprenoids play important ecological and physiological roles in plants. They also have a tremendous impact on human lives as food additives, medicines, and industrial raw materials, among others. Though some isoprenoids are highly abundant in nature, plants produce many at extremely low levels. Glandular trichomes (GT), which cover the aerial parts of more than 25% of vascular plants, have been considered as natural biofactories for the mass production of rare industrially important isoprenoids. In several plant genera (e.g., Lavandula and Mentha), GTs produce and store large quantities of the low molecular weight isoprenoids, in particular mono- and sesquiterpenes, as essential oil constituents. Within each trichome, a group of secretory cells is specialized to strongly and specifically express isoprenoid biosynthetic genes, and to synthesize and deposit copious amounts of terpenoids into the trichome's storage reservoir. Despite the abundance of certain metabolites in essential oils and defensive resins, plants, particularly those lacking glandular trichomes, accumulate small quantities of many of the biologically active and industrially important isoprenoids. Therefore, there is a pressing need for technologies to enable the mass production of such metabolites, and to help meet the ever-increasing demand for plant-based bioproducts, including medicines and renewable materials. Considerable contemporary research has focused on engineering isoprenoid metabolism in GTs, with the goal of utilizing them as natural biofactories for the production of valuable phytochemicals. In this review, we summarize recent advances related to the engineering of isoprenoid biosynthetic pathways in glandular trichomes. [ABSTRACT FROM AUTHOR]

Plants can use volatiles for remote suppression of competitors. Mints produce essential oils, which are known to affect the growth of other plants. We used a comparative approach to identify allelopathic compounds from different Mints (genus Mentha, but also including Cat Mint, Nepeta cataria, and Corean Mint, Agastache rugosa, belonging to sisters clades within the Mentheae) using the standard cress germination assay as readout. To understand the mechanism behind this allelopathic effect, we investigated the response of tobacco BY-2 cell lines, expressing GFP-tagged markers for microtubules and actin filaments to these essential oils. Based on the comparison between bioactivity and chemical components, we identified menthone as prime candidate for the allelopathic effect, and confirmed this bioactivity targeted to microtubules experimentally in both, plant cells (tobaccoBY-2), and seedlings (Arabidopsis thaliana). We could show that menthone disrupted microtubules and induced mortality linked with a rapid permeabilization (less than 15 min) of the plasma membrane. This mortality was elevated in a tubulin marker line, where microtubules are mildly stabilized. Our study paves the way for the development of novel bioherbicides that would be environmentally friendly.

Mentha is a strongly scented herb of the Lamiaceae (formerly Labiatae) and includes about 30 species and hybrid species that are distributed or introduced throughout the globe. These fragrant plants have been selected throughout millennia for use by humans as herbs, spices, and pharmaceutical needs. The distilling of essential oils from mint began in Japan and England but has become a significant industrial product for the US, China, India, and other countries. The US Department of Agriculture (USDA), Agricultural Research Service, National Clonal Germplasm Repository (NCGR) maintains a mint genebank in Corvallis, Oregon. This facility preserves and distributes about 450 clones representing 34 taxa, hybrid species, advanced breeder selections, and F1 hybrids. Mint crop wild relatives are included in this unique resource. The majority of mint accessions and hybrids in this collection were initially donated in the 1970s by the A.M. Todd Company, located in Kalamazoo, Michigan. Other representatives of diverse mint taxa and crop wild relatives have since been obtained from collaborators in Australia, New Zealand, Europe, and Vietnam. These mints have been evaluated for cytology, oil components, verticillium wilt resistance, and key morphological characters. Pressed voucher specimens have been prepared for morphological identity verification. An initial set of microsatellite markers has been developed to determine clonal identity and assess genetic diversity. Plant breeders at private and public institutions are using molecular analysis to determine identity and diversity of the USDA mint collection. Evaluation and characterization includes essential oil content, disease resistance, male sterility, and other traits for potential breeding use. These accessions can be a source for parental genes for enhancement efforts to produce hybrids, or for breeding new cultivars for agricultural production. Propagules of Mentha are available for distribution to international researchers as stem cuttings, rhizome cuttings, or seed, which can be requested through the GRIN-Global database of the US National Plant Germplasm System, subject to international treaty and quarantine regulations.

Plants can use volatiles for remote suppression of competitors. Mints produce essential oils, which are known to affect the growth of other plants. We used a comparative approach to identify allelopathic compounds from different Mints (genus Mentha , but also including Cat Mint, Nepeta cataria , and Corean Mint, Agastache rugosa , belonging to sisters clades within the Mentheae) using the standard cress germination assay as readout. To understand the mechanism behind this allelopathic effect, we investigated the response of tobacco BY-2 cell lines, expressing GFP-tagged markers for microtubules and actin filaments to these essential oils. Based on the comparison between bioactivity and chemical components, we identified menthone as prime candidate for the allelopathic effect, and confirmed this bioactivity targeted to microtubules experimentally in both, plant cells (tobaccoBY-2), and seedlings (Arabidopsis thaliana). We could show that menthone disrupted microtubules and induced mortality linked with a rapid permeabilization (less than 15 min) of the plasma membrane. This mortality was elevated in a tubulin marker line, where microtubules are mildly stabilized. Our study paves the way for the development of novel bioherbicides that would be environmentally friendly. [ABSTRACT FROM AUTHOR]

Mentha is a strongly scented herb of the Lamiaceae (formerly Labiatae) and includes about 30 species and hybrid species that are distributed or introduced throughout the globe. These fragrant plants have been selected throughout millennia for use by humans as herbs, spices, and pharmaceutical needs. The distilling of essential oils from mint began in Japan and England but has become a significant industrial product for the US, China, India, and other countries. The US Department of Agriculture (USDA), Agricultural Research Service, National Clonal Germplasm Repository (NCGR) maintains a mint genebank in Corvallis, Oregon. This facility preserves and distributes about 450 clones representing 34 taxa, hybrid species, advanced breeder selections, and F1 hybrids. Mint crop wild relatives are included in this unique resource. The majority of mint accessions and hybrids in this collection were initially donated in the 1970s by the A.M. Todd Company, located in Kalamazoo, Michigan. Other representatives of diverse mint taxa and crop wild relatives have since been obtained from collaborators in Australia, New Zealand, Europe, and Vietnam. These mints have been evaluated for cytology, oil components, verticillium wilt resistance, and key morphological characters. Pressed voucher specimens have been prepared for morphological identity verification. An initial set of microsatellite markers has been developed to determine clonal identity and assess genetic diversity. Plant breeders at private and public institutions are using molecular analysis to determine identity and diversity of the USDA mint collection. Evaluation and characterization includes essential oil content, disease resistance, male sterility, and other traits for potential breeding use. These accessions can be a source for parental genes for enhancement efforts to produce hybrids, or for breeding new cultivars for agricultural production. Propagules of Mentha are available for distribution to international researchers as stem cuttings, rhizome cuttings, or seed, which can be requested through the GRIN-Global database of the US National Plant Germplasm System, subject to international treaty and quarantine regulations. [ABSTRACT FROM AUTHOR]