MOLECULAR ANALYSIS OF FLORAL PIGMENTATION IN THE ORCHID, BROMHEADIA FINLAYSONIANA

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.

Author dc:creator

• LIEW CHYE FONG