title: Global characterization of Artemisia annua glandular trichome transcriptome using 454 pyrosequencing.
abstract: BACKGROUND
  Glandular trichomes produce a wide variety of commercially important secondary metabolites in many plant species. The most prominent anti-malarial drug artemisinin, a sesquiterpene lactone, is produced in glandular trichomes of Artemisia annua. However, only limited genomic information is currently available in this non-model plant species.
  
  
  RESULTS
  We present a global characterization of A. annua glandular trichome transcriptome using 454 pyrosequencing. Sequencing runs using two normalized cDNA collections from glandular trichomes yielded 406,044 expressed sequence tags (average length = 210 nucleotides), which assembled into 42,678 contigs and 147,699 singletons. Performing a second sequencing run only increased the number of genes identified by approximately 30%, indicating that massively parallel pyrosequencing provides deep coverage of the A. annua trichome transcriptome. By BLAST search against the NCBI non-redundant protein database, putative functions were assigned to over 28,573 unigenes, including previously undescribed enzymes likely involved in sesquiterpene biosynthesis. Comparison with ESTs derived from trichome collections of other plant species revealed expressed genes in common functional categories across different plant species. RT-PCR analysis confirmed the expression of selected unigenes and novel transcripts in A. annua glandular trichomes.
  
  
  CONCLUSIONS
  The presence of contigs corresponding to enzymes for terpenoids and flavonoids biosynthesis suggests important metabolic activity in A. annua glandular trichomes. Our comprehensive survey of genes expressed in glandular trichome will facilitate new gene discovery and shed light on the regulatory mechanism of artemisinin metabolism and trichome function in A. annua.
authors.affiliation: Department of Biology and the State Key Lab for Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong SAR, PR China. wangwei@cuhk.edu.hk
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Yejun
authors.initials: Y
authors.lastname: Wang
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhang
authors.forename: Yan
authors.initials: Y
authors.lastname: Qi
authors.forename: Dianjing
authors.initials: D
authors.lastname: Guo
mesh_terms: D000595:Amino Acid Sequence; D031172:Artemisia annua / Q000201:enzymology / Q000235:genetics*; D037621:Artemisinins / Q000378:metabolism; D020451:Contig Mapping; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D020224:Expressed Sequence Tags; D020869:Gene Expression Profiling; D017343:Genes, Plant; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D037621:Artemisinins; D018076:DNA, Complementary; D018744:DNA, Plant