Characterization, expression and phylogenetic study of R2R3-MYB genes in orchid.

cDNA fragments representing 21 R2R3-MYB genes were isolated by RT-PCR from the Dendrobium orchid hybrid Woo Leng. Six full-length cDNA clones were obtained from a flower cDNA library, four of which, DwMYB1, DwMYB2, DwMYB8 and DwMYB10, represent typical plant R2R3-MYB genes. The conceptual DwMYB4 protein is truncated at the C-terminal region and contains the R2 repeat and the N-terminal half of the R3 repeat (R2R3'). DwMYB4 expression is restricted to flowers. DwMYB9 contains an 8 amino acid N-terminal deletion in the R2 repeat (R2'R3) and is expressed at high levels in mature flower and inflorescence, but at very low levels in young flower buds. DwMYB8 and DwMYB10 show similar expression patterns and share very high sequence similarity in the N-terminal part of the MYB domain. Analysis of amino acid substitution indicated that the pattern and type of substitution between Arabidopsis and maize are quite different. Maize may have more conserved substitution in the MYB(BRH) domain than Arabidopsis.