Cloning and functional characterization of a beta-pinene synthase from Artemisia annua that shows a circadian pattern of expression.
Artemisia annua plants produce a broad range of volatile compounds, including monoterpenes, which contribute to the characteristic fragrance of this medicinal species. A cDNA clone, QH6, contained an open reading frame encoding a 582-amino acid protein that showed high sequence identity to plant monoterpene synthases. The prokaryotically expressed QH6 fusion protein converted geranyl diphosphate to (-)-beta-pinene and (-)-alpha-pinene in a 94:6 ratio. QH6 was predominantly expressed in juvenile leaves 2 weeks postsprouting. QH6 transcript levels were transiently reduced following mechanical wounding or fungal elicitor treatment, suggesting that this gene is not directly involved in defense reaction induced by either of these treatments. Under a photoperiod of 12 h/12 h (light/dark), the abundance of QH6 transcripts fluctuated in a diurnal pattern that ebbed around 3 h before daybreak (9th h in the dark phase) and peaked after 9 h in light (9th h in the light phase). The contents of (-)-beta-pinene in juvenile leaves and in emitted volatiles also varied in a diurnal rhythm, correlating strongly with mRNA accumulation. When A. annua was entrained by constant light or constant dark conditions, QH6 transcript accumulation continued to fluctuate with circadian rhythms. Under constant light, advanced cycles of fluctuation of QH6 transcript levels were observed, and under constant dark, the cycle was delayed. However, the original diurnal pattern could be regained when the plants were returned to the normal light/dark (12 h/12 h) photoperiod. This is the first report that monoterpene biosynthesis is transcriptionally regulated in a circadian pattern.
Lu
Shan
S
National Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
Xu
Ran
R
Jia
Jun-Wei
JW
Pang
Jihai
J
Matsuda
Seiichi P T
SP
Chen
Xiao-Ya
XY
D000595:Amino Acid Sequence; D031172:Artemisia annua / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D001483:Base Sequence; D000081008:Bicyclic Monoterpenes; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D019753:Intramolecular Lyases / Q000235:genetics* / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D039821:Monoterpenes / Q000378:metabolism; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018547:Plant Stems / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
D000081008:Bicyclic Monoterpenes; D001643:Bridged Bicyclo Compounds; D018076:DNA, Complementary; D039821:Monoterpenes; D010940:Plant Proteins; D014157:Transcription Factors; C010789:beta-pinene; D019753:Intramolecular Lyases; C040265:pinene cyclase I; C005451:alpha-pinene