Abstract
Artemisinin, a sesquiterpenoid endoperoxide, isolated from the plant Artemisia annua L., is widely used in the treatment of malaria. Another sesquiterpenoid, β-caryophyllene having antibiotic, antioxidant, anticarcinogenic and local anesthetic activities, is also presented in A. annua. The role played by sesquiterpene transporters in trichomes and accumulation of these metabolites is poorly understood in A. annua and in trichomes of other plant species. We identified AaPDR3, encoding a pleiotropic drug resistance (PDR) transporter located to the plasma membrane from A. annua. Expression of AaPDR3 is tissue-specifically and developmentally regulated in A. annua. GUS activity is primarily restricted to T-shaped trichomes of old leaves and roots of transgenic A. annua plants expressing proAaPDR3: GUS. The level of β-caryophyllene was decreased in transgenic A. annua plants expressing AaPDR3-RNAi while transgenic A. annua plants expressing increased levels of AaPDR3 accumulated higher levels of β-caryophyllene. When AaPDR3 was expressed in transformed yeast, yeasts expressing AaPDR3 accumulated more β-caryophyllene, rather than germacrene D and β-farnesene, compared to the non-expressing control.
Highlights
ATP-binding-cassette (ABC) proteins are one of the biggest protein families in plants, which function as channels, molecular switches, and transporters (Sugiyama et al, 2006)
We analyzed the expression of a PDR transporter PDR3 (AaPDR3) after the treatment with 100 μM MeJA, showing that MeJA induced the expression of AaPDR3 in A. annua (Figure S2)
These findings show that pleiotropic drug resistance (PDR) genes are predominately expressed in roots and leaves
Summary
ATP-binding-cassette (ABC) proteins are one of the biggest protein families in plants, which function as channels, molecular switches, and transporters (Sugiyama et al, 2006). FPP is converted to an array of cyclization products, such as amorpha-4,11-diene, β-caryophyllene, β-farnesene, germacrene A, and epi-cedrol, by amorpha-4,11-diene synthase (AaADS; Bouwmeester et al, 1999), β-caryophyllene synthase (AaCPS; Cai et al, 2002), β-farnesene synthase (AaBFS; Picaud et al, 2005), germacrene A synthase (AaGAS; Bertea et al, 2006), and epi-cedrol synthase (AaECS; Mercke et al, 1999) respectively in A. annua It is well-known that geranyl diphosphate (GPP) is the precursor of monoterpenes. The authors cloned PDR1 and PDR2 transporters from A. annua and suggested that PDR2 was related to artemisinin biosynthesis in tobacco, the substrate was not verified (Wang et al, 2016) These findings indicate that the multicellular T-shaped trichomes have the capacity to synthesize and store large quantities of sesquiterpenes in A. annua. We identified a PDR transporter involved in β-caryophyllene transport in A. annua
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