Comparison of transcripts in Phalaenopsis bellina and Phalaenopsis equestris (Orchidaceae) flowers to deduce monoterpene biosynthesis pathway.
BACKGROUND
Floral scent is one of the important strategies for ensuring fertilization and for determining seed or fruit set. Research on plant scents has hampered mainly by the invisibility of this character, its dynamic nature, and complex mixtures of components that are present in very small quantities. Most progress in scent research, as in other areas of plant biology, has come from the use of molecular and biochemical techniques. Although volatile components have been identified in several orchid species, the biosynthetic pathways of orchid flower fragrance are far from understood. We investigated how flower fragrance was generated in certain Phalaenopsis orchids by determining the chemical components of the floral scent, identifying floral expressed-sequence-tags (ESTs), and deducing the pathways of floral scent biosynthesis in Phalaneopsis bellina by bioinformatics analysis.


RESULTS
The main chemical components in the P. bellina flower were shown by gas chromatography-mass spectrometry to be monoterpenoids, benzenoids and phenylpropanoids. The set of floral scent producing enzymes in the biosynthetic pathway from glyceraldehyde-3-phosphate (G3P) to geraniol and linalool were recognized through data mining of the P. bellina floral EST database (dbEST). Transcripts preferentially expressed in P. bellina were distinguished by comparing the scent floral dbEST to that of a scentless species, P. equestris, and included those encoding lipoxygenase, epimerase, diacylglycerol kinase and geranyl diphosphate synthase. In addition, EST filtering results showed that transcripts encoding signal transduction and Myb transcription factors and methyltransferase, in addition to those for scent biosynthesis, were detected by in silico hybridization of the P. bellina unigene database against those of the scentless species, rice and Arabidopsis. Altogether, we pinpointed 66% of the biosynthetic steps from G3P to geraniol, linalool and their derivatives.


CONCLUSIONS
This systems biology program combined chemical analysis, genomics and bioinformatics to elucidate the scent biosynthesis pathway and identify the relevant genes. It integrates the forward and reverse genetic approaches to knowledge discovery by which researchers can study non-model plants.
Hsiao
Yu-Yun
YY
Department of Life Sciences, National Cheng-Kung University, Tainan 701, Taiwan. yunhsiao@mail2000.com.tw
Tsai
Wen-Chieh
WC
Kuoh
Chang-Sheng
CS
Huang
Tian-Hsiang
TH
Wang
Hei-Chia
HC
Wu
Tian-Shung
TS
Leu
Yann-Lii
YL
Chen
Wen-Huei
WH
Chen
Hong-Hwa
HH
D000080462:Acyclic Monoterpenes; D015152:Blotting, Northern; D019295:Computational Biology; D016208:Databases, Factual; D020224:Expressed Sequence Tags; D035264:Flowers / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005986:Glyceraldehyde 3-Phosphate / Q000378:metabolism; D008084:Lipoxygenase / Q000235:genetics / Q000378:metabolism; D008956:Models, Chemical; D039821:Monoterpenes / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D009812:Odorants / Q000032:analysis; D029595:Orchidaceae / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D010476:Perfume / Q000737:chemistry; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D014158:Transcription, Genetic / Q000235:genetics; D014835:Volatilization
D000080462:Acyclic Monoterpenes; D039821:Monoterpenes; D010476:Perfume; D010940:Plant Proteins; D012333:RNA, Messenger; D005986:Glyceraldehyde 3-Phosphate; D019289:Pyruvic Acid; C018584:linalool; D008084:Lipoxygenase