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The glandular secretory trichomes ( GSTs) on Artemisia annua leaves have the capacity to secrete and store artemisinin, a compound which is the most effective treatment for uncomplicated malaria. An effective strategy to improve artemisinin content is therefore to increase the density of GSTs in A. annua. However, the formation mechanism of GSTs remains poorly understood., To explore the mechanisms of GST initiation in A. annua, we screened myeloblastosis ( MYB) transcription factor genes from a GST transcriptome database and identified a MIXTA transcription factor, Aa MIXTA1, which is expressed predominantly in the basal cells of GST in A. annua. Overexpression and repression of Aa MIXTA1 resulted in an increase and decrease, respectively, in the number of GSTs as well as the artemisinin content in transgenic plants., Transcriptome analysis and cuticular lipid profiling showed that Aa MIXTA1 is likely to be responsible for activating cuticle biosynthesis. In addition, dual-luciferase reporter assays further demonstrated that Aa MIXTA1 could directly activate the expression of genes related to cuticle biosynthesis., Taken together, Aa MIXTA1 regulated cuticle biosynthesis and prompted GST initiation without any abnormal impact on the morphological structure of the GSTs and so provides a new way to improve artemisinin content in this important medicinal plant. [ABSTRACT FROM AUTHOR]

Artemisinin has attracted interest due to its medicinal value in treating malaria and its potential for use against certain cancers and viral diseases. Trichome density and capacity determine artemisinin content in Artemisia annua plants. Thus, the ATP-binding cassette transporter G (ABCG) subfamily involved in trichome cuticle development may also influence artemisinin accumulation. In this study, putative A. annua ABC transporter unigenes were identified and classified from the unigene sequences up to date in the National Center for Biotechnology Information database, and nine putative A. annua ABCG transporter unigenes that may be involved in cuticle development were selected for expression analyses. Two of them, AaABCG6 and AaABCG7, showed parallel expression pattern as two artemisinin biosynthesis-specific genes (amorpha-4, 11-diene synthase and a cytochrome P450-dependent hydroxylase, CYP71AV1) in different tissues and different leaf development stages and also showed similar induction in the plants after methyl jasmonate or abscisic acid treatments. Identification of these putative A. annua ABCG transporter unigenes could provide the basis for cloning of the full-length genes and further functional investigation to find the artemisinin relevant transporters, which could be used for improving artemisinin yield in both A. annua plants and heterologous systems using transgenic technology. [ABSTRACT FROM AUTHOR]

emisinin is currently the best therapeutic against both drug-resistant and cerebral-malaria-causing strains of Plasmodium falciparum. Allene oxide cyclase (AOC) is the key enzyme in the biosynthetic pathway of jasmonates. In this study, a full-length cDNA of AOC gene (named as AaAOC) was cloned from Artemisia annua L. AaAOC was 1,007 bp, containing an open reading frame (750 bp) encoding 249 amino acids. Comparative and bioinformatic analyses revealed that the deduced protein of AaAOC was highly homologous to AOC from other plant species. Phylogenetic analysis indicated that AaAOC was clustered in a closely related subgroup with AOC of Camptotheca acuminata. Southern blot analysis revealed that AaAOC was a multicopy gene. Reverse transcriptase-polymerase chain reaction (RT-PCR) and QPCR analysis showed that AaAOC mRNA accumulated most abundantly in alabastrums, in which the content of artemisinin was previously proven to be the highest. RT-PCR analysis revealed that MeJA, ABA, and ethylene treatments significantly enhanced AaAOC transcript expression. And the results of HPLC showed that the contents of artemisinin were greatly increased after the treatments of ABA and MeJA. [ABSTRACT FROM AUTHOR]

Tetraploid Artemisia annua plants were successfully inducted by using colchicine, and their ploidy was confirmed by flow cytometry. Higher stomatal length but lower frequency in tetraploids were revealed and could be considered as indicators of polyploidy. The average level of artemisinin in tetraploids was increased from 39% to 56% than that of the diploids during vegetation period, as detected by high-performance liquid chromatography-evaporative light scattering detector. Gene expressions of 10 key enzymes related to artemisinin biosynthetic pathway in different ploidy level were analyzed by semiquantitative polymerase chain reaction and significant upregulation of FPS, HMGR, and artemisinin metabolite-specific Aldh1 genes were revealed in tetraploids. Slight increased expression of ADS was also detected. Our results suggest that higher artemisinin content in tetraploid A. annua may result from the upregulated expression of some key enzyme genes related to artemisinin biosynthetic pathway. [ABSTRACT FROM AUTHOR]