thase and C encodes dihydroflavonol reductase (Harper,
1976). Chalcone synthase converts a colorless precursor
into a colorless product; while dihydroflavonol reductase
converts a colorless precursor into the colored anthocyanin skeleton.
Besides the structural genes that encode enzymes, there
are regulatory genes that encoded proteins which control the expression of the structural genes. Anthocyanin
biosynthesis requires the coordinated expression of three
regulatory genes (Myc, Myb and Wd). A WD protein
serves as a platform to bind a MYC protein. The MYC
protein then binds a MYB protein to the platform. The
MYB protein binds directly to a specific target structural
gene to activate its expression.
In Phalaenopsis, anthocyanin biosynthesis requires the
coordinated expression of the three regulatory gene (Myc,
Myb and Wd) and two structural genes (R and C) described above for Cattleya. In purple flowers R, C, Myb,
Myc and Wd genes are expressed. While in white flowers,
only R, Myc and Wd genes are expressed. The absence of
Myb gene expression is responsible for the absence of C
gene expression, resulting is the lack of dihydroflavonol
4-reductase and white flowers. The same situation exists in
anthocynin-patterned flowers (i.e., spotted and striped).
The Myb and C genes are expressed in the spots or stripes,
but not in the white background. There is no difference
in R, Wd and Myc gene expression between the spots or
stripes and background (Ma, Pooler and Griesbach, 2009).
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References
Griesbach, R.J. 1984. Effects of carotenoid anthocyanin combinations
on flower color., J. Heredity 75:145-147.
Griesbach, R.J. 1990. Flavonoid copigments and anthocyanin of
Phalaenopsis schillerana., Lindleyana 5:231-234.
Griesbach, R.J., 1997. The biochemical basis for the blue flower color
mutations in Doritis pulcherrima and Phalaenopsis violacea.,
Lindleyana 12:64-71.
Griesbach, R.J. 2005. A scientific approach to breeding blue orchids.,
Orchids 74:376-379.
Griesbach, R.J., 2005. Biochemistry and genetics of flower color.,
Plant Breeding Reviews 25:89-114.
Harper, J. W. 1976. Genetic control of orchid pigments., Proc. 1st
Symp. Sci. Aspects of Orchids, Chem. Dept., Univ. of Detroit.,
p. 90-105.
Hurst, C.C., 1909. Inheritance of albinism in orchids., Gardener
Chronicles (3) 45:81-82.
Ma, H., Pooler, M., and Griesbach, R. 2009. Anthocyanin regulatory/
structural gene expression in Phalaenopsis., J. Amer. Soc. Hort. Sci.
134:88-96.
Tatsuzawa, F., Saito, N., Seki, H., Hara, R., Yokoi, M., and Honda, T.,
1997. Acylated cyanidin glycosides in the red-purple flowers of
Phalaenopsis., Phytochemitsry 45:173-177.
22
Phalaenopsis | Third Quarter | Volume 23 | 2013
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