CHARACTERIZATION OF FLAVONOL SYNTHASE AND LEUCOANTHOCYANIDIN DIOXYGENASE GENES IN ARABIDOPSIS - FURTHER EVIDENCE FOR DIFFERENTIAL REGULATION OF EARLY AND LATE GENES

As part of an ongoing investigation into the organization and regulati on of the flavonoid biosynthetic pathway, two Arabidopsis thaliana exp ressed sequence tag (EST) clones (153O10T7 and YAY780) with high homol ogy to leucoanthocyanidin dioxygenase (LDOX) or flavonol synthase (FLS ) were identified. EST YAY780 was sequenced and found to encode a prot ein 49 to 78% identical to all LDOX sequences in the database. EST 153 O10T7 was used to isolate a genomic clone encoding a protein with 59 t o 61% sequence identity to petunia (Petunia hybrida) and potato (Solan um tuberosum) FLS. DNA blot analysis was used to screen the Arabidopsi s genome for sequences related to FLS and LDOX and to determine the po sitions of the two clones on the RI map. The expression patterns of FL S and LDOX in etiolated seedlings moved to white light and in two puta tive regulatory mutants (ttg and tt8) were determined by RNA blot anal ysis. These studies indicate that FLS is an ''early'' flavonoid gene i n Arabidopsis seedlings, whereas LDOX is a ''late'' gene. Furthermore, FLS is the first flavonoid enzyme identified in Arabidopsis that may be encoded by a gene family.