AUTHOR=Zhang Fangyuan , Liu Wanhong , Xia Jing , Zeng Junlan , Xiang Lien , Zhu Shunqin , Zheng Qiumin , Xie He , Yang Chunxian , Chen Min , Liao Zhihua 

TITLE=Molecular Characterization of the 1-Deoxy-D-Xylulose 5-Phosphate Synthase Gene Family in Artemisia annua

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00952

DOI=10.3389/fpls.2018.00952

ISSN=1664-462X

ABSTRACT=<p><italic>Artemisia annua</italic> produces artemisinin, an effective antimalarial drug. In recent decades, the later steps of artemisinin biosynthesis have been thoroughly investigated; however, little is known about the early steps of artemisinin biosynthesis. Comparative transcriptomics of glandular and filamentous trichomes and <sup>13</sup>CO<sub>2</sub> radioisotope study have shown that the 2-C-methyl-<sc><sc>D</sc></sc>-erythritol-4-phosphate (MEP) pathway, rather than the mevalonate pathway, plays an important role in artemisinin biosynthesis. In this study, we have cloned three <italic>1-deoxy-<sc>D</sc>-xylulose 5-phosphate synthase</italic> (<italic>DXS</italic>) genes from <italic>A</italic>. <italic>annua</italic> (<italic>AaDXS1</italic>, <italic>AaDXS2</italic>, and <italic>AaDXS3</italic>); the DXS enzyme catalyzes the first and rate-limiting enzyme of the MEP pathway. We analyzed the expression of these three genes in different tissues in response to multiple treatments. Phylogenetic analysis revealed that each of the three <italic>DXS</italic> genes belonged to a distinct clade. Subcellular localization analysis indicated that all three AaDXS proteins are targeted to chloroplasts, which is consistent with the presence of plastid transit peptides in their N-terminal regions. Expression analyses revealed that the expression pattern of <italic>AaDXS2</italic> in specific tissues and in response to different treatments, including methyl jasmonate, light, and low temperature, was similar to that of artemisinin biosynthesis genes. To further investigate the tissue-specific expression pattern of <italic>AaDXS2</italic>, the promoter of <italic>AaDXS2</italic> was cloned upstream of the <italic>β-glucuronidase</italic> gene and was introduced in arabidopsis. Histochemical staining assays demonstrated that <italic>AaDXS2</italic> was mainly expressed in the trichomes of Arabidopsis leaves. Together, these results suggest that <italic>AaDXS2</italic> might be the only member of the DXS family in <italic>A. annua</italic> that is involved in artemisinin biosynthesis.</p>