Molecular Cloning and Bacterial Expression of Germacrene A Synthase cDNA from Crepidiastrum sonchifolium

Germacrene A synthase（GAS） catalyzes the biosynthesis of germacrene A, which is a key precursor for sesquiterpone lactones. Cloning of a novel full-length cDNA encoding GAS from the medicinal plant Crepidiastrum sonchifolium（dosignated CsGAS） is reported in this study. The cDNA is 1837 bp long and contains a 1680-bp open reading frame encoding a 559 amino-acid protein. The functional expression of the cDNA in Escherichia coli, as an N-terminal thioredoxin fusion protein, with the pET32a vector yielding a recombinant enzyme. Sequence analysis was used to compare this enzyme with the mechanistically related epi-aristolochene synthase from tobacco, and the effect of possible involvement of a number of amino acids in sesquiterpone synthase on product specificity was also discussed.

Identification of a Unique Germacrene A Oxidase from Xanthium strumarium

8,12-sesquiterpene lactones(STLs)are an important class of natural products with unique pharmaceutical activities.For years the pathway leading to 8,12-STLs remains an enigma.Xanthium strumarium accumulates abundant 8,12-STLs,and xanthatin is a characteristic 8,12-STL in it.Xanthatin has been previously postulated to be derived from germacrene A,but the steps from germacrene A to xanthatin are unknown.As part of an effort to understand the xanthatin biosynthetic pathway.This study reports the characterization of a unique germacrene A oxidase(XsGAO)from X.strumarium.Unlike a classical GAO enzyme,which is known to catalyze a three-step oxidation of germarene A to yield germacrene A acid(GAA),surprisingly,XsGAO catalyzed only one-step conversion of germacrene A to germacrene A alcohol.We discussed that GAO may be pressured to acquire a novel activity during the evolutionary path for the biosynthesis of 8,12-STLs.

Chemical Compositions of the Leaf Essential Oils of <i>Aralia spinosa</i>from Three Habitats in Northern Alabama

Aralia spinosa leaves were collected from three different habitats in north Alabama. The leaf essential oils were collected by hydrodistillation and analyzed by gas chromatography / mass spectrometry (GC-MS). The most abundant components of A. spinosa essential oils were the sesquiterpenes germacrene D (28.0% - 37.3%), (E)-caryophyllene (8.2% - 15.7%), and α-humulene (1.9% - 4.9%);the monoterpene myrcene (up to 15.1%), and the fatty-acid-derivative (2E)-hexenal (trace to 28.9%). Fatty-acid derivatives and monoterpene hydrocarbons were more abundant in samples from suburban Huntsville than those from “natural” habitats (Monte Sano Mountain, Wheeler National Wildlife Refuge), while sesquiterpene hydrocarbons were more abundant in the natural/wild samples.

Chemical Composition and Antibacterial Activity of Essential Oils from <i>Struchium sparganophora</i>Linn. Ktze Asteraceae

Struchium sparganophora Linn. Ktze Asteraceae is a culinary herb that is consumed in the Western part of Nigeria and has wide medicinal uses in traditional medicine. The present study was carried out to determine the chemical composition of the oils from its leaf and stem and their antibacterial activity. Essential oils were collected from the leaf and stem of Struchium sparganophora by hydrodistillation and analysed by GC and GC-MS. The antimicrobial activity was tested against Gram negative (G-ve) and Gram positive (G + ve) microorganisms obtained from the Medical Microbiology Unit, University College Hospital (UCH), Ibadan, Nigeria. Forty-six compounds were identified in the leaf representing 95.3% of the total oil while fifty-five compounds were identified in the stem representing 93.5% of the oil. β-caryophyllene, Germacrene A, a-humulene and Germacrene D represented the major components in both oils. Antibacterial activity of the oils against certain strains of bacteria showed that the different concentrations of the oils (100 – 10,000 ppm) from the leaf had activity ranging from 9.0 ± 1.0 to 14.3 ± 2.55 mm while that from the stem had activity ranging from 18.5 ± 2.2 to 20.0 ± 0.0 mm for both G-ve.and G + ve microorganisms respectively.

Terpenes of the Essential Oil from Ipomoea alba Leaf in Response to Herbivore and Mechanical Injuries

There is no doubt that the chemical composition of plants,including norvolatile and volatile compounds,is widely affected by abiotic and biotic stress.Plants are able to biosynthesize a variety of secondary metabolites against actions of natural enemies,such as herbivores,fungus,virus and bacteria.The present study revealed that the chemical compositions of leaf essential oils from Ipomoea alba underwent quantitative and qualitative alterations both when infested with the grasshopper Elaeochlora trilineata and mechanically damaged.Grasshopper attack and mechanical wounding induced the biosynthesis of nine volatile compounds in leaves of I.alba:cumene,α-ylangene,β-panasinsene,β-gurjunene aromadendrene,β-funebrene,spirolepechinene,cubenol and sclareolide.The amount of germacrene D(33.2%to 20.4%)decreased when the leaves were mechanically damaged;but when the leaves were attacked by a grasshopper,the germacrene D increased from 33.2%to 39.4%.The results showed that I.alba leaves clearly responded to abiotic and biotic stress and contribute to an understanding of plant responses to stress conditions.

A chromosome-scale genome assembly of Artemisia argyi reveals unbiased subgenome evolution and key contributions of gene duplication to volatile terpenoid diversity

Artemisia argyi Le´vl.et Vant.,a perennial Artemisia herb with an intense fragrance,is widely used in traditional medicine in China and many other Asian countries.Here,we present a chromosome-scale genome assembly of A.argyi comprising 3.89 Gb assembled into 17 pseudochromosomes.Phylogenetic and comparative genomic analyses revealed that A.argyi underwent a recent lineage-specificwhole-genomeduplication(WGD)event after divergence fromArtemisia annua,resulting in two subgenomes.Wedeciphered the diploid ancestral genome of A.argyi,and unbiased subgenome evolution was observed.The recent WGD led to a large number of duplicated genes in the A.argyi genome.Expansion of the terpene synthase(TPS)gene family through various types of gene duplication may have greatly contributed to the diversity of volatile terpenoids in A.argyi.In particular,we identified a typical germacrene D synthase gene cluster within the expanded TPS gene family.The entire biosynthetic pathways of germacrenes,(+)-borneol,and(+)-camphor were elucidated in A.argyi.In addition,partial deletion of the amorpha-4,11-diene synthase(ADS)gene and loss of function of ADS homologs may have resulted in the lack of artemisinin production in A.argyi.Our study provides newinsights into the genome evolution of Artemisia and lays a foundation for further improvement of the quality of this important medicinal plant.