The Transcriptome Responses Involved In Artemisinin Biosynthesis In Artemisia Annua L. Under UV-B Radiation

Artemisinin, an endoperoxide sesquiterpene lactone produced by the traditional Chinese medicinal herb Artemisia annua L., is an effective drug against cerebral malaria and chloroquine-resistant strains of Plasmodium falciparum. There is an enormous demand for artemisinin supply all over the world. However, its low content in A. annua limits the commercialization of artemisinin production greatly. Attempts were made to improve the artemisinin production by optimizing chemical and physical environmental factors or by elicitation of abiotic and biotic factors. Ultraviolet B(UV-B) radiation(wavelength range 280 to 320 nm), a natural component of solar radiation, has been proved to affect humans, animals, plants and ecosystem. Moreover, after UV-B irradiation, plants display diverse morphological and physiological responses likely to be involved in signal transduction cascades and gene expression in the biosynthesis of secondary metabolites.In the present study, to study the effect of UV-B on gene expression and artemisinin biosynthesis, a low dose(1.44 k J m-2 d-1) of UV-B radiation was applied to A. annua seedlings. The mechanism of induction has also been investigated preliminarily here.Firstly, to study the physiological responses in A. annua, about 2-month-old plants were treated with UV-B for 10 days. 10-day period UV-B treatment(1 h per day) enhanced the content of artemisinin and photosynthetic pigments in A. annua leaves, also caused foliar injury and cell death estimated by Evans blue staining.Here, we focused on transcriptional changes in A. annua under UV-B radiation. A total of 358 transcripts were identified as differentially expressed under UV-B stress using an Agilent Gene Chip with 43,692 probe sets, of which 172 transcripts increased and 186 transcripts decreased in abundance. Bioinformatic analysis indicated UV-B-induced genes were enriched in response to stress, reactive oxygen species, and hormone(ethylene, ABA) stimulus.Finally, up-regulated transcripts related to signal transduction and antioxidant defense systems via its complex signaling cascade may play important roles in protection and artemisinin biosynthesis. UV-B treatment induced the generation of reactive oxygen species(ROS) including H2O2 and O2-, enhanced peroxidase activity and endogenous content of ABA in A. annua leaves. The content of ABA in UV-B treated group reached almost 2- and 1.5-fold on day 8 and 10, respectively.This is the first study on global gene expression patterns during UV-B stress in A. annua. The obtained results provide novel information for understanding the complexity of UV-B responses and further identification of the enzymes involve in artemisinin biosynthesis. Such work proposes an effective approach to use UV-B radiation as elicitor in plant secondary metabolite production and provides a potential application for artemisinin production in A. annua.