Diversification of the duplicated F3h genes in Triticeae.

The F3h gene encodes the flavonoid synthesis enzyme flavanone 3-hydroxylase. Unlike most plant genomes, the bread wheat (Triticum aestivum L.) B genome has two, rather than just one F3h copy. The paralogous F3h-B2 sequence was isolated by PCR and shown to be transcribed, but its predicted polypeptide differed from the typical F3H sequence at a number of the conserved residues associated with its putative substrate-binding sites. The F3h-B2 promoter region was highly divergent from that of F3h-B1, and the transcriptional profiles of the two genes were distinct. Among a panel of 95 Triticeae accessions, representing 24 species, an F3h-2 copy was only detected within those carrying a B, S, G, or an R genome. Analysis of the coding sequence divergence suggested that a small segmental duplication occurred early in the evolution of the Triticeae tribe. The duplicated F3h copy appears to have acquired a novel function in the progenitor of the closely related B, G, and S genomes, as well as in the R genome. In other Triticeae genomes, the F3h-2 paralog may have been lost following pseudogenization.