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Next generation sequencing unravels the biosynthetic ability of spearmint (Mentha spicata) peltate glandular trichomes through comparative transcriptomics.

Jin J, Panicker D, Wang Q, Kim MJ, Liu J, Yin JL, Wong L, Jang IC, Chua NH, Sarojam R - BMC Plant Biol. (2014)

Bottom Line: A significant number of these unigenes remained unannotated or encoded hypothetical proteins.We found 16 terpene synthases (TPS), 18 cytochrome P450s, 5 lipid transfer proteins and several transcription factors that were preferentially expressed in PGT.Among the 16 TPSs, two were characterized biochemically and found to be sesquiterpene synthases.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Plant glandular trichomes are chemical factories with specialized metabolic capabilities to produce diverse compounds. Aromatic mint plants produce valuable essential oil in specialised glandular trichomes known as peltate glandular trichomes (PGT). Here, we performed next generation transcriptome sequencing of different tissues of Mentha spicata (spearmint) to identify differentially expressed transcripts specific to PGT. Our results provide a comprehensive overview of PGT's dynamic metabolic activities which will help towards pathway engineering.

Results: Spearmint RNAs from 3 different tissues: PGT, leaf and leaf stripped of PGTs (leaf-PGT) were sequenced by Illumina paired end sequencing. The sequences were assembled de novo into 40,587 non-redundant unigenes; spanning a total of 101 Mb. Functions could be assigned to 27,025 (67%) unigenes and among these 3,919 unigenes were differentially expressed in PGT relative to leaf - PGT. Lack of photosynthetic transcripts in PGT transcriptome indicated the high levels of purity of isolated PGT, as mint PGT are non-photosynthetic. A significant number of these unigenes remained unannotated or encoded hypothetical proteins. We found 16 terpene synthases (TPS), 18 cytochrome P450s, 5 lipid transfer proteins and several transcription factors that were preferentially expressed in PGT. Among the 16 TPSs, two were characterized biochemically and found to be sesquiterpene synthases.

Conclusions: The extensive transcriptome data set renders a complete description of genes differentially expressed in spearmint PGT. This will facilitate the metabolic engineering of mint terpene pathway to increase yield and also enable the development of strategies for sustainable production of novel or altered valuable compounds in mint.

No MeSH data available.


Trichomes on spearmint leaf. (A) Scanning electron microscope image of spearmint leaf showing three types of trichomes, a, Non glandular hairy trichome; b, Peltate glandular trichome (PGT); c, Capitate glandular trichome. (B) Process of secretion by PGT. a, presecretory stage; b, formation of storage cavity; c, secretion into the storage cavity; d, release of oil upon injury. The PGTs were stained with toulidine blue.
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Fig1: Trichomes on spearmint leaf. (A) Scanning electron microscope image of spearmint leaf showing three types of trichomes, a, Non glandular hairy trichome; b, Peltate glandular trichome (PGT); c, Capitate glandular trichome. (B) Process of secretion by PGT. a, presecretory stage; b, formation of storage cavity; c, secretion into the storage cavity; d, release of oil upon injury. The PGTs were stained with toulidine blue.

Mentions: Spearmint leaves produce three different types of trichomes on their surfaces: non-glandular multicellular hair like, capitate glandular trichomes with a single secretory head cell and PGTs whose secretory head is composed of eight-cells with a single stalk and basal cell (Figure 1A). These PGT glands possess a large subcuticular storage space that is formed by the separation of the cuticle from the apical cells and the essential oil is secreted into this cavity [12] (Figure 1B). It is known that new glands keep initiating on the leaf till expansion ceases and the monoterpene content and compositions change with the age of the leaf [13-16]. Different studies have indicated that monoterpene biosynthesis is most active in young 12–20 day old leaves of peppermint after which the rate of synthesis slowly declines [17-19]. We performed gas chromatography–mass spectrometry (GC-MS) analysis on young spearmint leaves (about 1–2 cm in length) and found abundance of both limonene and carvone monoterpenes (Figure 2). Limonene is the first committed step towards carvone pathway. In addition to these monoterpenes, the presence of sesquiterpenes was also observed. This indicated the dynamic terpene biosynthetic activity of leaves at this stage of development. PGT were purified from leaves of this stage and RNA isolated. The leaves of the same stage were brushed to remove all trichomes and RNA extracted from them as controls (Additional file 1).Figure 1


Next generation sequencing unravels the biosynthetic ability of spearmint (Mentha spicata) peltate glandular trichomes through comparative transcriptomics.

Jin J, Panicker D, Wang Q, Kim MJ, Liu J, Yin JL, Wong L, Jang IC, Chua NH, Sarojam R - BMC Plant Biol. (2014)

Trichomes on spearmint leaf. (A) Scanning electron microscope image of spearmint leaf showing three types of trichomes, a, Non glandular hairy trichome; b, Peltate glandular trichome (PGT); c, Capitate glandular trichome. (B) Process of secretion by PGT. a, presecretory stage; b, formation of storage cavity; c, secretion into the storage cavity; d, release of oil upon injury. The PGTs were stained with toulidine blue.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4232691&req=5

Fig1: Trichomes on spearmint leaf. (A) Scanning electron microscope image of spearmint leaf showing three types of trichomes, a, Non glandular hairy trichome; b, Peltate glandular trichome (PGT); c, Capitate glandular trichome. (B) Process of secretion by PGT. a, presecretory stage; b, formation of storage cavity; c, secretion into the storage cavity; d, release of oil upon injury. The PGTs were stained with toulidine blue.
Mentions: Spearmint leaves produce three different types of trichomes on their surfaces: non-glandular multicellular hair like, capitate glandular trichomes with a single secretory head cell and PGTs whose secretory head is composed of eight-cells with a single stalk and basal cell (Figure 1A). These PGT glands possess a large subcuticular storage space that is formed by the separation of the cuticle from the apical cells and the essential oil is secreted into this cavity [12] (Figure 1B). It is known that new glands keep initiating on the leaf till expansion ceases and the monoterpene content and compositions change with the age of the leaf [13-16]. Different studies have indicated that monoterpene biosynthesis is most active in young 12–20 day old leaves of peppermint after which the rate of synthesis slowly declines [17-19]. We performed gas chromatography–mass spectrometry (GC-MS) analysis on young spearmint leaves (about 1–2 cm in length) and found abundance of both limonene and carvone monoterpenes (Figure 2). Limonene is the first committed step towards carvone pathway. In addition to these monoterpenes, the presence of sesquiterpenes was also observed. This indicated the dynamic terpene biosynthetic activity of leaves at this stage of development. PGT were purified from leaves of this stage and RNA isolated. The leaves of the same stage were brushed to remove all trichomes and RNA extracted from them as controls (Additional file 1).Figure 1

Bottom Line: A significant number of these unigenes remained unannotated or encoded hypothetical proteins.We found 16 terpene synthases (TPS), 18 cytochrome P450s, 5 lipid transfer proteins and several transcription factors that were preferentially expressed in PGT.Among the 16 TPSs, two were characterized biochemically and found to be sesquiterpene synthases.

View Article: PubMed Central - PubMed

ABSTRACT

Background: Plant glandular trichomes are chemical factories with specialized metabolic capabilities to produce diverse compounds. Aromatic mint plants produce valuable essential oil in specialised glandular trichomes known as peltate glandular trichomes (PGT). Here, we performed next generation transcriptome sequencing of different tissues of Mentha spicata (spearmint) to identify differentially expressed transcripts specific to PGT. Our results provide a comprehensive overview of PGT's dynamic metabolic activities which will help towards pathway engineering.

Results: Spearmint RNAs from 3 different tissues: PGT, leaf and leaf stripped of PGTs (leaf-PGT) were sequenced by Illumina paired end sequencing. The sequences were assembled de novo into 40,587 non-redundant unigenes; spanning a total of 101 Mb. Functions could be assigned to 27,025 (67%) unigenes and among these 3,919 unigenes were differentially expressed in PGT relative to leaf - PGT. Lack of photosynthetic transcripts in PGT transcriptome indicated the high levels of purity of isolated PGT, as mint PGT are non-photosynthetic. A significant number of these unigenes remained unannotated or encoded hypothetical proteins. We found 16 terpene synthases (TPS), 18 cytochrome P450s, 5 lipid transfer proteins and several transcription factors that were preferentially expressed in PGT. Among the 16 TPSs, two were characterized biochemically and found to be sesquiterpene synthases.

Conclusions: The extensive transcriptome data set renders a complete description of genes differentially expressed in spearmint PGT. This will facilitate the metabolic engineering of mint terpene pathway to increase yield and also enable the development of strategies for sustainable production of novel or altered valuable compounds in mint.

No MeSH data available.