Overexpression of a type-I isopentenyl pyrophosphate isomerase of Artemisia annua in the cytosol leads to high arteannuin B production and artemisinin increase.

We recently characterized a gene-terpene network that is associated with artemisinin biosynthesis in self-pollinated (SP) Artemisia annua, an effective antimalarial plant. We hypothesize that an alteration of gene expression in the network may improve the production of artemisinin and its precursors. In this study, we cloned an isopentenyl pyrophosphate isomerase (IPPI) cDNA, AaIPPI1, from Artemisia annua (Aa). The full-length cDNA encodes a type-I IPPI containing a plastid transit peptide (PTP) at its amino terminus. After the removal of the PTP, the recombinant truncated AaIPPI1 isomerized isopentenyl pyrophosphate (IPP) to dimethyl allyl pyrophosphate (DMAPP) and vice versa. The steady-state equilibrium ratio of IPP/DMAPP in the enzymatic reactions was approximately 1:7. The truncated AaIPPI1 was overexpressed in the cytosol of the SP A. annua variety. The leaves of transgenic plants produced approximately 4% arteannuin B (g g-1 , dry weight, dw) and 0.17-0.25% artemisinin (g g-1 , dw), the levels of which were significantly higher than those in the leaves of wild-type plants. In addition, transgenic plants showed an increase in artemisinic acid production of more than 1% (g g-1 , dw). In contrast, isoprene formation was significantly reduced in transgenic plants. These results provide evidence that overexpression of AaIPPI1 in the cytosol can lead to metabolic alterations of terpenoid biosynthesis, and show that these transgenic plants have the potential to yield high production levels of arteannuin B as a new precursor source for artemisinin.

Characterization of development and artemisinin biosynthesis in self-pollinated Artemisia annua plants.

Artemisia annua L. is the only natural resource that produces artemisinin (Qinghaosu), an endoperoxide sesquiterpene lactone used in the artemisinin-combination therapy of malaria. The cross-hybridization properties of A. annua do not favor studying artemisinin biosynthesis. To overcome this problem, in this study, we report on selection of self-pollinated A. annua plants and characterize their development and artemisinin biosynthesis. Self-pollinated F2 plants selected were grown under optimized growth conditions, consisting of long day (16 h of light) and short day (9 h of light) exposures in a phytotron. The life cycles of these plants were approximately 3 months long, and final heights of 30-35 cm were achieved. The leaves on the main stems exhibited obvious morphological changes, from indented single leaves to odd, pinnately compound leaves. Leaves and flowers formed glandular and T-shaped trichomes on their surfaces. The glandular trichome densities increased from the bottom to the top leaves. High performance liquid chromatography-mass spectrometry-based metabolic profiling analyses showed that leaves, flowers, and young seedlings of F2 plants produced artemisinin. In leaves, the levels of artemisinin increased from the bottom to the top of the plants, showing a positive correlation to the density increase of glandular trichomes. RT-PCR analysis showed that progeny of self-pollinated plants expressed the amorpha-4, 11-diene synthase (ADS) and cytochrome P450 monooxygenase 71 AV1 (CYP71AV1) genes, which are involved in artemisinin biosynthesis in leaves and flowers. The use of self-pollinated A. annua plants will be a valuable approach to the study of artemisinin biosynthesis.

Overexpression of Artemisia annua Cinnamyl Alcohol Dehydrogenase Increases Lignin and Coumarin and Reduces Artemisinin and Other Sesquiterpenes.

Artemisia annua is the only medicinal crop that produces artemisinin for malarial treatment. Herein, we describe the cloning of a cinnamyl alcohol dehydrogenase (AaCAD) from an inbred self-pollinating (SP) A. annua cultivar and its effects on lignin and artemisinin production. A recombinant AaCAD was purified via heterogeneous expression. Enzyme assays showed that the recombinant AaCAD converted p-coumaryl, coniferyl, and sinapyl aldehydes to their corresponding alcohols, which are key intermediates involved in the biosynthesis of lignin. Km, Vmax, and Vmax/Km values were calculated for all three substrates. To characterize its function in planta, AaCAD was overexpressed in SP plants. Quantification using acetyl bromide (AcBr) showed significantly higher lignin contents in transgenics compared with wild-type (WT) plants. Moreover, GC-MS-based profiling revealed a significant increase in coumarin contents in transgenic plants. By contrast, HPLC-MS analysis showed significantly reduced artemisinin contents in transgenics compared with WT plants. Furthermore, GC-MS analysis revealed a decrease in the contents of arteannuin B and six other sesquiterpenes in transgenic plants. Confocal microscopy analysis showed the cytosolic localization of AaCAD. These data demonstrate that AaCAD plays a dual pathway function in the cytosol, in which it positively enhances lignin formation but negatively controls artemisinin formation. Based on these data, crosstalk between these two pathways mediated by AaCAD catalysis is discussed to understand the metabolic control of artemisinin biosynthesis in plants for high production.

Xanosporic acid, an intermediate in bacterial degradation of the fungal phototoxin cercosporin.

The red fungal perylenequinone phototoxin cercosporin is oxidized by Xanthomonas campestris pv zinniae to a non-toxic, unstable green metabolite xanosporic acid, identified via its lactone as 1,12-bis(2'R-hydroxypropyl)-4,9-dihydroxy-6,7-methylenedioxy-11-methoxy-3-oxaperylen-10H-10-one-2-carboxylic acid. Xanosporolactone was isolated in approximately 2:1 ratio of M:P atropisomers.

Natural zinniol derivatives from Alternaria tagetica. Isolation, synthesis, and structure-activity correlation.

Two novel phytotoxins, 8-zinniol methyl ether (5) and 8-zinniol acetate (6), in addition to 6-(3',3'-dimethylallyloxy)-4-methoxy-5-methylphthalide (2), 5-(3',3'-dimethylallyloxy)-7-methoxy-6-methylphthalide (3), and the novel metabolites 8-zinniol 2-(phenyl)ethyl ether (4) and 7-zinniol acetate (7) have been identified as natural zinniol derivatives from the organic crude extract of Alternaria tagetica culture filtrates. Using zinniol as the starting material, phytotoxin 5 was synthesized, together with a number of synthetic intermediates (8-13). Both natural and synthetic zinniol derivatives were evaluated in the leaf-spot bioassay against marigold leaves (Tagetes erecta).