Computational and evolutionary insights into anthocyanin biosynthesis

its closest wild relative (Wang et al, 1999). Grasses were thought to have evolved

around 55 million years ago and the age of Solanceae is about ~ 40 million years. It

has been reported by El-Sayed et al ., (2008) that Purple corn ( Zea mays ), a member

of poacea family, contains high concentration of anthocyanins (1277µg/g); much

higher than other anthocyanin-rich sources whereas some members of solanaceae

contain lesser or no anthocyanins such as cultivated tomatoes.

Enormous variations with respect to color and pigmentation patterns are observed

between plant species. Anthocyanins are major pigments that contribute colors to

different parts of the plants and help to attract pollinators. Any genetic alerations

in structural and regulatory genes of anthocyanin biosynthesis will lead to

variation in anthocyanin content, color and pigment patterns. Rausher et al . (1997)

reportd that adaptive evolution of flower color governed more by regulatory genes

because regulatory genes in anthocyanin pathway tend to evolve faster than the

structural genes they regulate. Espley et al . (1997) reported that red colouration

in apple fruit is due to the activity of a MYB transcription factor, MdMYB10

which regulate anthocyanins. Dias et al . (2003) reported that after duplication of

maize R2R3 Myb genes, divergence of C-terminal regions of these genes occurred

due to accumulation of substitutions during evolution and showed that divergent

C termini of these R2R3 MYB proteins were subjected to purifying selection.

Phylogenetic and evolutionary analyses of CHS gene family of Viola cornuta with

maize, petunia, grape and Ipomoea have been studied by Farzad et al . (2005).

Extensive research on the evolution of the CHS gene family has been conducted

in Petunia. Rausher et al. (1999) compared the six core anthocyanin structural

genes CHS, CHI, F3H, DFR, ANS and UF3GT in maize sequences to Ipomoea

and Antirrhinum and found more than fivefold difference of nonsynonymous

substitution rate between CHS and UF3GT. Durbin et al ., (2000) suggested that

different duplicate copies of CHS in Morning glory have acquired specialized

functional roles over the course of evolution. Durbin et al. , (2000) found that

Morning glory contains a six-member gene family exhibiting sequence similarity

to chalcone synthases from other plants. Three of these copies CHS-A, CHS-B and

CHS-C were unable to convert 4-coumaroyl-CoA and malonyl-CoA to naringenin

chalcone, two of these copies CHS-A, CHS-B were capable of catalyzing the

condensation reaction while the sixth copy was a pseudogene. Hof et al . (2008)

compared the CHS gene lineage tree and the plastid species phylogeny of Viola

and indicated that the different CHS copies in Viola were the products of both

recent and more ancient duplications. Lu and Rausher (2003) analyzed the rate

variation of anthocyanin genes and concluded that downstream enzymes evolve

faster than upstream enzymes. This might be due to reduced selective constraint

of downstream enzymes than upstream genes. They also observed the variation

in synonymous and nonsynonymous substitution rates in CHS, ANS , and UF3GT.

The same UF3GT showed higher amino acid substitution rate, ANS an intermediate

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