MOLECULAR ANALYSIS OF FLORAL PIGMENTATION IN THE ORCHID, BROMHEADIA FINLAYSONIANA
LIEW CHYE FONG
LIEW CHYE FONG
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Abstract
This project involved the isolation and characterisation of cDNAs in the
flavonoid biosynthetic pathway of a local species of orchid, Bromheadia finlaysoniana
(Lindl.) Rchb. F. A cDNA library was constructed from the fully-opened flowers of
Bromheadia finlaysoniana. cDNA clones encoding phenylalanine ammonia-lyase
(PAL), chalcone synthase (CHS), flavanone 3-hydroxylase (F3H) and dihydroflavonol
4-reductase (DFR) were then isolated by screening the cDNA library with respective
polymerase chain reaction (PCR) generated homologous probes. Southern blot
analysis revealed that PAL, CHS and F3H are encoded by small multigene families
while DFR is represented by a single gene in the genome of Bromheadia.
Northern blot and reverse transcriptase-PCR (RT-PCR) analysis showed that
PAL is preferentially expressed in flowers and expressed at low levels in young leaves rich in
Anthocyanin. PAL expression is also found to be transiently induced in leaves after
wounding. CHS and F3H shared a similar pattern of expression in different plant parts
indicating that they are coordinately regulated. Both CHS and F3H were expressed at
very high levels in young leaves but at much lower levels in mature whole flowers.
DFR expression however is spatially regulated and coincides well with anthocyanin
accumulation.
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Date
1998
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