Transgenic Artemisia Annua Research Articles

Engineering Nootkatone Biosynthesis in Artemisia annua.

Nootkatone is a valuable sesquiterpene widely used in the food, fragrance, and flavor industries. Its price is very high due to its limited production in grapefruit peels or Alaska cypress heartwoods. Chemical synthesis of nootkatone uses heavy metals, highly flammable compounds, and strong oxidants, which cause severe damage to the environment. In this study, nootkatone is synthesized in Artemisia annua, using synthetic biology methods. Engineered Artemisia annua coexpressing valencene synthase (VS) and valencene oxidase (VO) in the cytosol produced nootkatone ranging from 0.89 to 8.52 μg/g fresh weight (FW). Furthermore, transgenic Artemisia annua coexpressing farnesyl diphosphate synthase (FPS), VS, and VO in plastids produced nootkatone ranging from 12.11 to 47.80 μg/g FW. These results indicated that engineering nootkatone biosynthesis in plastids was superior to that in the cytosol. Meanwhile, artemisinin production was unaltered in nootkatone-producing Artemisia annua. Our study developed a green approach for producing nootkatone in Artemisia annua with great market potential.

T-shaped trichome-specific expression of monoterpene synthase ADH2 using promoter-β-GUS fusion in transgenic Artemisia annua L.

Artemisinin, a sesquiterpene lactone isolated from Artemisia annua L. (sweet wormwood), is extensively used in the treatment of malaria. In order to better understand the metabolism of terpenes in A. annua and the influence of terpene synthases on artemisinin yield, the expression pattern of a monoterpene alcohol dehydrogenase (ADH2) has been studied using transgenic plants expressing promoter-β-glucuronidase (GUS) fusion. ADH2 played a major role in monoterpenoid biosynthesis including carveol, borneol, and artemisia ketone through in vitro biochemical analysis. In this study, the ADH2 promoter was cloned by the genome walking method. A number of putative cis-acting elements were predicted in promoter region, suggesting that the ADH2 is driven by a complex regulation mechanism. ADH2 gene was highly expressed in old leaves, whereas the artemisinin biosynthetic genes were mainly expressed in bud and young leaves. The expression of ADH2 gene increased quickly during leaf development, revealed by qRT-PCR. GUS expression analysis in different tissues of transgenic A. annua demonstrates that ADH2 expression is exclusively located to T-shaped trichome, not glandular secretory trichome.

Effects of overexpression of AaWRKY1 on artemisinin biosynthesis in transgenic Artemisia annua plants

The effective anti-malarial medicine artemisinin is costly because of the low content in Artemisia annua. Genetic engineering of A. annua is one of the most promising approaches to improve the yield of artemisinin. In this work, the transcription factor AaWRKY1, which is thought to be involved in the regulation of artemisinin biosynthesis, was cloned from A. annua var. Chongqing and overexpressed using the CaMV35S promoter or the trichome-specific CYP71AV1 promoter in stably transformed A. annua plants. The transcript level of AaWRKY1 was increased more than one hundred times under the CaMV35S promoter and about 40 times under the CYP71AV1 promoter. The overexpressed AaWRKY1 activated the transcription of CYP71AV1 and moreover the trichome-specific overexpression of AaWRKY1 improved the transcription of CYP71AV1 much more effectively than the constitutive overexpression of AaWRKY1, i.e. up to 33 times as compared to the wild-type plant. However the transcription levels of FDS, ADS, and DBR2 did not change significantly in transgenic plants. The significantly up-regulated CYP71AV1 promoted artemisinin biosynthesis, i.e. up to about 1.8 times as compared to the wild-type plant. It is demonstrated that trichome-specific overexpression of AaWRKY1 can significantly activate the transcription of CYP71AV1 and the up-regulated CYP71AV1 promotes artemisinin biosynthesis.

T-DNA Insertion Alters the Terpenoid Content Composition and Bioactivity of Transgenic Artemisia annua

In this study, the interference of T-DNA insertion upon Agrobacterium-mediated transformation on the biochemical expression of the host genome is discussed. Plant extracts of transgenic Artemisia annua L. with or without an overexpressed famesyl pyrophosphate synthase gene have been investigated for their bioactivity and metabolic profile in comparison with wild type A. annua. The highest antimicrobial activity against Staphylococcus aureus, Bacillus subtilis and Candida albicans was observed in the T253 transgenic lines. Moreover, the crude extract from T253 showed higher antimalarial activity against the Plasmodium faciparum K1 strain than those of the others. The terpenoid constituents and antimicrobial properties of the plant samples were grouped by hierarchical clustering analysis. The clustering showed that squalene is a putative compound that might be involved in increasing the bioactivity of the transgenic line. In addition, T253 had a triterpene content that was about twice as great as that of the T253-2 line, which had a higher content of sesquiterpenes. However, both lines were transformed by the same FPS gene. These results suggested that the different bioactive properties observed in each transgenic line may be caused by variations in their terpenoid composition, which is affected by T-DNA insertion at different positions in the host plant.

Enhanced artemisinin accumulation and metabolic profiling of transgenic Artemisia annua L. plants over-expressing by rate-limiting enzymes from isoprenoid pathway

Artemisinin, a natural product isolated from aerial parts of Artemisia annua L. plant, is a potent antimalarial drug against drug-resistant malaria. In recent times, the demand (101–119 MT) for artemisinin is exponentially increasing with the increased incidence of drug-resistant malaria throughout the world, especially African and Asian continents. However, the commercial production of artemisinin-based combination therapies has limitation because of the presence of low concentration of artemisinin in plants. Therefore, transgenic lines of A. annua L. plants over-expressing both HMG-Co A reductase (hmgr) and amorpha-4, 11-diene synthase (ads) genes were developed to enhance the content of artemisinin. The selected transgenic lines (TR4, TR5, and TR7) were found to accumulate higher artemisinin (0.97–1.2%) as compared to the non-transgenic plants (0.63%). The secondary metabolite profiles of these lines were also investigated employing gas chromatography mass spectrometry, which revealed a clear difference in these metabolites in transgenic and non-transgenic lines of A. annua L. at different growth and developmental stages. The major metabolites reported in these lines at pre-flowering stage were related to essential oil and chlorophyll biosynthesis (71.33% in TR5 transgenic lines vs. 61.70% in non-transgenic line). Based on these results, we concluded that over-expression of both hmgr and ads genes in A. annua L. plants results not only increase in artemisinin content, but also enhances synthesis of other isoprenoid including essential oil. It is also evident from this study that the novel artemisinin-rich varieties of A. annua L. could be developed by suppressing essential oil biosynthesis, so that more carbon could preferentially be diverted from mevalonate pathway to artemisinin biosynthesis.

Studies on the Expression of Sesquiterpene Synthases Using Promoter-β-Glucuronidase Fusions in Transgenic Artemisia annua L

In order to better understand the influence of sesquiterpene synthases on artemisinin yield in Artemisia annua, the expression of some sesquiterpene synthases has been studied using transgenic plants expressing promoter-GUS fusions. The cloned promoter sequences were 923, 1182 and 1510 bp for β-caryophyllene (CPS), epi-cedrol (ECS) and β-farnesene (FS) synthase, respectively. Prediction of cis-acting regulatory elements showed that the promoters are involved in complex regulation of expression. Transgenic A. annua plants carrying promoter-GUS fusions were studied to elucidate the expression pattern of the three sesquiterpene synthases and compared to the previously studied promoter of amorpha-4,11-diene synthase (ADS), a key enzyme of artemisinin biosynthesis. The CPS and ECS promoters were active in T-shaped trichomes of leaves and stems, basal bracts of flower buds and also in some florets cells but not in glandular secretory trichome while FS promoter activity was only observed in leaf cells and trichomes of transgenic shoots. ADS, CPS, ECS and FS transcripts were induced by wounding in a time depended manner. The four sesquiterpene synthases may be involved in responsiveness of A. annua to herbivory. Methyl jasmonate treatment triggered activation of the promoters of all four sesquiterpene synthases in a time depended manner. Southern blot result showed that the GUS gene was inserted into genomic DNA of transgenic lines as a single copy or two copies. The relative amounts of CPS and ECS as well as germacrene A synthase (GAS) transcripts are much lower than that of ADS transcript. Consequently, down-regulation of the expression of the CPS, ECS or GAS gene may not improve artemsinin yield. However, blocking the expression of FS may have effects on artemisinin production.

Studies on the expression of linalool synthase using a promoter-β-glucuronidase fusion in transgenic Artemisia annua

Artemisinin, an antimalarial endoperoxide sesquiterpene, is synthesized in glandular trichomes of Artemisia annua L. A number of other enzymes of terpene metabolism utilize intermediates of artemisinin biosynthesis, such as isopentenyl and farnesyl diphosphate, and may thereby influence the yield of artemisinin. In order to study the expression of such enzymes, we have cloned the promoter regions of some enzymes and fused them to β-glucuronidase (GUS). In this study, we have investigated the expression of the monoterpene synthase linalool synthase (LIS) using transgenic A. annua carrying the GUS gene under the control of the LIS promoter. The 652bp promoter region was cloned by the genome walker method. A number of putative cis-acting elements were predicted indicating that the LIS is driven by a complex regulation mechanism. Transgenic plants carrying the promoter-GUS fusion showed specific expression of GUS in T-shaped trichomes (TSTs) but not in glandular secretory trichomes, which is the site for artemisinin biosynthesis. GUS expression was observed at late stage of flower development in styles of florets and in TSTs and guard cells of basal bracts. GUS expression after wounding showed that LIS is involved in plant responsiveness to wounding. Furthermore, the LIS promoter responded to methyl jasmonate (MeJA). These results indicate that the promoter carries a number of cis-acting regulatory elements involved in the tissue-specific expression of LIS and in the response of the plant to wounding and MeJA treatment. Southern blot analysis indicated that the GUS gene was integrated in the A. annua genome as single or multi copies in different transgenic lines. Promoter activity analysis by qPCR showed that both the wild-type and the recombinant promoter are active in the aerial parts of the plant while only the recombinant promoter was active in roots. Due to the expression in TSTs but not in glandular trichomes, it may be concluded that LIS expression will most likely have little or no effect on artemisinin production.

Promotion of artemisinin biosynthesis in transgenic Artemisia annua by overexpressing ADS, CYP71AV1 and CPR genes

Artemisinin is an effective anti-malarial drug isolated from A. annua, which has an enormous commercialization demand all over the world. However, the low artemisinin content of A. annua greatly limits the commercialization of artemisinin. In this study, we report the results of our experiments, where for the first time we have achieved the overexpression of ADS, CYP71AV1 and CPR genes in A. annua. Eight transgenic A. annua plants were obtained through Agrobacterium tumefaciens-mediated transformation, which was confirmed by PCR. Southern-blot analyses showed that some of the transgenic lines had low copies of the integration transgenes. The results of real time-qPCR showed that the expression levels of ADS, CYP71AV1 and CPR genes were significantly increased, too. The HPLC analyses showed that the artemisinin contents were significantly increased in these transgenic plants. One of the transgenic plants, ACR16, was found to contain 2.4-fold higher (15.1mg/g DW) artemisinin than the control plants (pCAMBIA2300 transgenic plants). All above results showed that overexpression of ADS, CYP71AV1 and CPR genes in A. annua could promoted the metabolic flux flows toward biosynthesis of artemisinin and effectively increase the level of artemisinin content in transgenic A. annua plants.

Validation of Artemisia Genus-Specific Gene, GEL4, for Use as an Endogenous Reference Gene in Qualitative PCR Detection of Putative Transgenic Artemisia annua

Abstract Artemisia annua L. is a popular medical plant used against malaria. Transgenic A. annua plants have been developed to increase the artemisinin content using genetic engineering. To develop a reliable PCR method of detecting transgenic A. annua, one Artemisia specific gene, GEL4, was selected and validated as suitable. Qualitative PCR methods were assayed with 16 different A. annua ecotypes and four Artemisia plants, and identical amplified products were obtained. No amplified products were observed when genomic DNA samples were extracted from 15 different plant species. An LOD of 0.05 ng of A. annua DNA was also determined. Furthermore, the results of a Southern blot method showed that the GEL4 gene was in three copies of the six A. annua ecotypes tested. To determine whether there was intraspecific variability in the GEL4 region between different A. annua ecotypes, the GEL4 region corresponding to the 10 A. annua ecotypes was cloned and sequenced. Alignment of the obtained sequences presented a highly conserved amplification product region in 10 A. annua ecotypes. Therefore, it is concluded that the GEL4 gene can be used as an endogenous reference gene of A. annua, and that the qualitative PCR system was reliable for the detection of transgenic A. annua.

Characterization and comparison of three transgenic Artemisia annua varieties and wild-type variety in environmental release trial

Artemisinin, a sesquiterpene isolated from Artemsisia annua L. (Chinese wormwood) is an increasingly popular drug against malaria. In this study, three transgenic A. annua varieties with increased artemisinin content were evaluated in an environmental release trial. First, because there were risks concerning genetically modified plants, the 3 transgenic varieties were compared with that of wild-type plants in regard to agronomic traits, viability and expressed material. Second, stress tolerances (salt, drought and herbicide) were evaluated under experimental conditions. The results indicated significant differences between the 3 transgenic and wild-type plants in some agronomic traits (as in plant height, crown width, stem diameter, 1000-seeds weight), and no significant differences in leaf shape. Also, the viability (germination rate, transplant survival and seeds wintering ability) from both transgenic and control plants were similar. Moreover, it also was determined that the 3 transgenic and control plants had similar stress tolerances (salt tolerance, drought tolerance, herbicide tolerance). The expression of target genes in transgenic varieties was either enhanced or suppressed. Thus, the artemisinin content was increased in transgenic varieties as expected. Key words: Transgenic Artemisia annua, agronomic traits, viability, expressed materials, stress tolerances.

Terpenoid metabolic profiling analysis of transgenic Artemisia annua L. by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Amorpha-4,11-diene synthase (ADS) is a very important enzyme which catalyzes the committed step of artemisinin biosynthesis. In this work, two lines of transgenic Artemisia annua L. which ADS was over-expressed (line A9) and suppressed (line Amsi), respectively, were utilized. And the transgenic line GUS with β-Glucuronidase gene was regarded as the control. Their terpenoid metabolic profiling was investigated by using GC × GC–TOFMS. The metabolic profiling method established included simple extraction, two-dimension separation and multivariate analysis. Partial least squares discriminant analysis (PLS-DA) was used to classify two transgenic lines and the control line. Eleven important compounds in classification were identified. Most of them were sesquiterpenoids including monoterpenoid, diterpenoid and four bioprecursors of artemsisnin. Compared with the control, artemisinin and bioprecursors in the line A9 increased as a result of over-expressing ADS. Borneol and phytol also increased in the line A9, but (E)-β-farnesene and germacrene D were reversely altered. The result indicated that over-expression of the ADS affected not only artemisinin biosynthesis, but also the whole metabolic network of terpenoid. Compared with the line A9, no opposite change of artemisinin and related derivatives was observed in the line Amsi, the ADS inhibition had no significant effect on artemisinin biosynthesis in the line Amsi.

Synergistic re-channeling of mevalonate pathway for enhanced artemisinin production in transgenic Artemisia annua

To interfere with the endogenous gene encoding squalene synthase (SS) responsible for sterol biosynthesis, an antisense SS cDNA ( asSS) was introduced into the genome of A. annua. Following the decline of SS mRNA and synchronous reduction of total sterols, mRNA coding for amorpha-4,11-diene synthase (ADS) tremendously elevated, whereas mRNAs for sesquiterpene cyclases encompassing 8-epicedrol synthase (EPS), β-caryophyllene synthase (CS) and β-farnesene synthase (FS) declined or kept homeostasis, suggesting a bias in redirection of the partially blocked metabolic flow to amorpha-4,11-diene. By phenotyping the chimeric ADS promoter-fused β-glucuronidase gene ( pADS-GUS), overexpression of the pADS-GUS reporter was detected upon chilling exposure and ultraviolet (UV) irradiation. In transgenic plants that expose to chilling, ADS and EPS were dramatically up-regulated, but CS was down-regulated and FS and SS were unaffected, implying further chilling-induced diversion of carbon flux among sesquiterpenes. Accordingly, ADS and cytochrome P450 reductase (CPR) were also chilling-inducible, while cytochrome P450 monooxygenase (CYP71AV1) reflected a complicated chilling profile. A maximal artemisinin content was accounted for 16.6 mg/g or 3.7-fold increase in a chilled transgenic line. Fascinatingly, an extraordinarily high artemisinin content of 23.5 mg/g or 5.2-fold increase was measured after 15-month storage of the ground powder from the identical chilled transgenic tissue, demonstrating non-enzymatic conversion from a putative artemisinin precursor to artemisinin. Moreover, a relevance of chilling exposure with singlet oxygen ( 1O 2) emission and artemisinin overproduction was established. These results indicated that the mevalonate pathway has been first skewed to amorpha-4, 11-diene and shunted ultimately to artemisinin through a synergy of genetic modification with environmental superinduction.

Quantitative Transcript Profiling Reveals Down-Regulation of A Sterol Pathway Relevant Gene and Overexpression of Artemisinin Biogenetic Genes in TransgenicArtemisia annuaPlants

To investigate the dynamic fluctuation of terpenoid relevant transcriptomics in transgenic ARTEMISIA ANNUA plants that express the genomic integrated antisense squalene synthase gene ( ASSS), we have quantified the transcript levels of the sterol anabolic SS gene as well as artemisinin biogenetic amorphadiene synthase (ADS), cytochrome P450 monooxygenase (CYP71AV1) and cytochrome P450 reductase (CPR) genes by real-time fluorescent quantitative polymerase chain reaction (RFQ-PCR). The SS mRNA level in transgenic plants sharply droped to 7.4 % - 55.3 % (i. e., 44.7 - 92.6 % reduction as the wild-type control), strongly implying that the expression of endogenous SS gene is significantly suppressed by the exogenous ASSS gene. In a synchronous fashion, ADS, CYP71AV1 and CPR mRNA levels elevated with the decline of SS mRNA level in transgenic plants, and the maximal ADS, CYP71AV1 and CPR mRNA levels in transgenic plants were 3.0-, 4.4- and 2.5-fold, respectively, higher than those in the control. Without a lethal effect but with a distinguishable impact on the organogenesis and morphology of transgenic plants, the down-regulation of SS gene has also led to the coordinated overexpression of ADS, CYP71AV1 and CPR genes together with the overproduction of artemisinin although no fully perfect correlation among the available experimental data has been shown.