Dinabandhu

from Hordium vulgare in the place of Triticum aestivum and CHI from Solanum

melongena in the place of Petunia hybrid unavailability of the sequences in the

databases. In our study, McDonald and Kreitman analysis for positive selection

showed higher nonsynonymous substitution changes in downstream enzymes

DFR (171), ANS (166) and UF3GT (192) than upstream enzymes CHS (148)

and CHI (153) and F3H (160). Ka/Ks ratio among each gene between both plant

families was also substantially higher for downstream enzymes DFR, ANS and

UF3GT. McDonald and Kreitman (1991) proposed a test that compares the

synonymous and nonsynonymous variation within and between populations.

Rausher et al . (1999) concluded from their studies between plant species (morning

glory, snapdragon and maize) concluded that in anthocyanin pathway upstream

enzymes evolve more slowly than downstream enzymes. Similarly evolutionary

studies by Lu and Rausher (2003) in Ipomoea sp . concluded that the most upstream

enzyme, chalcone synthase-D (CHS-D), evolves more slowly than the two most

downstream enzymes, anthocyanidin synthase (ANS) and UDP glucose flavonoid

3-oxy-glucosyltransferase (UFGT). In this study, we observed same situation

for upstream enzyme as well as downstream enzymes by studying plant species

belonging to solanaceae and poaceae family. This indicates rapid evolution of

downstream enzymes than upstream enzymes between solanaceae and poaceae.

Between members of solanaceae and poaceae Ks was not available for CHS, DFR

and ANS indicating the synonymous substitutions of these genes between those

species have been saturated or close to saturation. Therefore, accurate estimation

of Ka/Ks was not possible individually for these genes. Mutation rate for slow

evolution of upstream enzymes were ruled out because Fisher’s exact test was

nonsignificant for all genes. Though CHS showed lower nonsynonymous changes,

it was also having higher synonymous changes between solanaceae and poaceae.

By assuming the mutation rate might not be the exact explanation of rate variation

between upstream and downstream enzymes, we conducted Tajima’s D test to

know whether there is action of purifying selection over these enzymes or not.

Tajima’D statistic was significantly negative for CHS and CHI indicating strong

purifying selection during course of their evolution. It was higher and positive

for downstream enzymes DFR, ANS and UF3GT. To support this interesting

evidence, we analysed the conserved DNA regions, polymorphic sites, segregating

sites and codon usage bias among these genes between solanaceae and poaceae.

The codon use bias significantly differs between solanaceae and poacea species

as these two are taxonomically divergent. Except F3H, GC content at third codon

position was higher in CHS and CHI than DFR, ANS and UF3GT between two

families. Effective number of codons (ENC) was higher in CHS and CHI than

others between solanaceae and poacea species. CHS and CHI also showed more

codon bias. The ENC and codon usage bias were higher for upstream enzymes.

Nucleotide diversity analysis showed that between both plants families CHI,ANS,

DFR are UF3GT are more diverse and CHS is least diverse. Multiple sequence

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International Journal of Bioinformatics and Biological Sciences : v.2 n.3&4. Dec. 2014