A. Gauthier et al., CDNA CLONING AND CHARACTERIZATION OF A 3' 5'-O-METHYLTRANSFERASE FOR PARTIALLY METHYLATED FLAVONOLS FROM CHRYSOSPLENIUM-AMERICANUM/, Plant molecular biology, 32(6), 1996, pp. 1163-1169
Enzymatic O-methylation of plant secondary metabolites is an important
mechanism for the inactivation of reactive hydroxyl groups and for th
e modification of their solubility. A cDNA clone (pFOMT3') encoding th
e gene for the 3'/5'-O-methylation of partially methylated flavonols w
as isolated from Chrysosplenium americanum (Saxifragaceae). We used a
PCR fragment obtained with degenerate oligonucleotides designed from c
onserved regions of various O-methyltransferases (OMTs). The pFOMT3' c
DNA sequence shows about 67-85% similarity to other plant OMT sequence
s. The recombinant protein expresses strict specificity for positions
3'/5' (meta) of partially methylated flavonols, but does not accept qu
ercetin or caffeic acid for further methylation. Southern blot analysi
s of the genomic DNA probed with an OMT sequence suggests the presence
of a number of related genes in this species, consistent with the mul
tiple enzymatic methylations involved in the biosynthesis of polymethy
lated flavonols in this plant.