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A Novel Class of Plant Type III Polyketide Synthase Involved in Orsellinic Acid Biosynthesis from Rhododendron dauricum

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ABSTRACT

Rhododendron dauricum L. produces daurichromenic acid, the anti-HIV meroterpenoid consisting of sesquiterpene and orsellinic acid (OSA) moieties. To characterize the enzyme responsible for OSA biosynthesis, a cDNA encoding a novel polyketide synthase (PKS), orcinol synthase (ORS), was cloned from young leaves of R. dauricum. The primary structure of ORS shared relatively low identities to those of PKSs from other plants, and the active site of ORS had a unique amino acid composition. The bacterially expressed, recombinant ORS accepted acetyl-CoA as the preferable starter substrate, and produced orcinol as the major reaction product, along with four minor products including OSA. The ORS identified in this study is the first plant PKS that generates acetate-derived aromatic tetraketides, such as orcinol and OSA. Interestingly, OSA production was clearly enhanced in the presence of Cannabis sativa olivetolic acid cyclase, suggesting that the ORS is involved in OSA biosynthesis together with an unidentified cyclase in R. dauricum.

No MeSH data available.


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Analyses of the tissue distributions of DCA and PKS transcripts in R. dauricum. (A) DCA content in various tissues, analyzed by HPLC. Numbers indicate young leaves (1), mature leaves (2), twigs (3), flowers (4), and roots (5). The data are means ± SD of triplicate assays. ND, not detected. (B) Semi-quantitative RT-PCR analyses of ORS and CHS gene expression. The 18S rRNA gene fragment was amplified as a housekeeping gene. Numbers indicate the same tissues as shown in (A).
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Figure 9: Analyses of the tissue distributions of DCA and PKS transcripts in R. dauricum. (A) DCA content in various tissues, analyzed by HPLC. Numbers indicate young leaves (1), mature leaves (2), twigs (3), flowers (4), and roots (5). The data are means ± SD of triplicate assays. ND, not detected. (B) Semi-quantitative RT-PCR analyses of ORS and CHS gene expression. The 18S rRNA gene fragment was amplified as a housekeeping gene. Numbers indicate the same tissues as shown in (A).

Mentions: The tissue-specific expression of ORS and CHS in R. dauricum plants was analyzed by semi-quantitative RT-PCR experiments, using gene-specific primers. As shown in Figure 9B, the ORS gene is clearly expressed at the highest level in young leaves, and in lesser amounts in mature leaves and twigs. This distribution pattern agreed well with the DCA content in each tissue (Figure 9A). In contrast, the CHS gene was mostly expressed in flowers, followed by young leaves. Thus, the CHS herein obtained seems to participate in the flavonoid biosynthesis in flowers and young leaves, as R. dauricum produces various flavonoids in these tissues (Qiang et al., 2011).


A Novel Class of Plant Type III Polyketide Synthase Involved in Orsellinic Acid Biosynthesis from Rhododendron dauricum
Analyses of the tissue distributions of DCA and PKS transcripts in R. dauricum. (A) DCA content in various tissues, analyzed by HPLC. Numbers indicate young leaves (1), mature leaves (2), twigs (3), flowers (4), and roots (5). The data are means ± SD of triplicate assays. ND, not detected. (B) Semi-quantitative RT-PCR analyses of ORS and CHS gene expression. The 18S rRNA gene fragment was amplified as a housekeeping gene. Numbers indicate the same tissues as shown in (A).
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5037138&req=5

Figure 9: Analyses of the tissue distributions of DCA and PKS transcripts in R. dauricum. (A) DCA content in various tissues, analyzed by HPLC. Numbers indicate young leaves (1), mature leaves (2), twigs (3), flowers (4), and roots (5). The data are means ± SD of triplicate assays. ND, not detected. (B) Semi-quantitative RT-PCR analyses of ORS and CHS gene expression. The 18S rRNA gene fragment was amplified as a housekeeping gene. Numbers indicate the same tissues as shown in (A).
Mentions: The tissue-specific expression of ORS and CHS in R. dauricum plants was analyzed by semi-quantitative RT-PCR experiments, using gene-specific primers. As shown in Figure 9B, the ORS gene is clearly expressed at the highest level in young leaves, and in lesser amounts in mature leaves and twigs. This distribution pattern agreed well with the DCA content in each tissue (Figure 9A). In contrast, the CHS gene was mostly expressed in flowers, followed by young leaves. Thus, the CHS herein obtained seems to participate in the flavonoid biosynthesis in flowers and young leaves, as R. dauricum produces various flavonoids in these tissues (Qiang et al., 2011).

View Article: PubMed Central - PubMed

ABSTRACT

Rhododendron dauricum L. produces daurichromenic acid, the anti-HIV meroterpenoid consisting of sesquiterpene and orsellinic acid (OSA) moieties. To characterize the enzyme responsible for OSA biosynthesis, a cDNA encoding a novel polyketide synthase (PKS), orcinol synthase (ORS), was cloned from young leaves of R. dauricum. The primary structure of ORS shared relatively low identities to those of PKSs from other plants, and the active site of ORS had a unique amino acid composition. The bacterially expressed, recombinant ORS accepted acetyl-CoA as the preferable starter substrate, and produced orcinol as the major reaction product, along with four minor products including OSA. The ORS identified in this study is the first plant PKS that generates acetate-derived aromatic tetraketides, such as orcinol and OSA. Interestingly, OSA production was clearly enhanced in the presence of Cannabis sativa olivetolic acid cyclase, suggesting that the ORS is involved in OSA biosynthesis together with an unidentified cyclase in R. dauricum.

No MeSH data available.


Related in: MedlinePlus