Abstract:

By using Thermal Asymmetric Interlaced PCR (TAIL-PCR) method, a DNA fragment of about 1 000 bp was amplified and cloned from a liverwort species (Lunularia cruciata (L.) Dum. ex Lindb). The nucleotide sequence of this fragment and its deduced amino acid sequence shared about 56% and 60% identity with those of exon 2 of CHS genes from vascular plants respectively. The four characteristic catalyzing sites of CHS were found conserved in the deduced amino acid sequences of the fragment when compared with other CHS sequences. This is the first report of cloning a CHS-like gene from liverworts, suggesting that the origin of CHS genes may predate liverworts. Using the CHS-like sequence from L. cruciata and CHS sequences from two fern-alien species, Psilotum nudum (L.) Griseb. and Equisetum arvense L., as outgroups, the phylogenetic trees of about 250 CHSs from 29 families of angiosperm plants were constructed by using the neighbour-joining (NJ), maximum parsimony (MP) and quartet puzzle (QP) methods. The results showed that the CHSs from most plant families were separated into two or more clades while sequences from the families Brassicaceae, Fabaceae and Poaceae were each grouped into an independent monophyletic clade. The relative base substitution rates were estimated for CHS genes in three plant families, Solanaceae, Convolvulaceae, and Asteraceae, where the heterogeneity rate was detected both within and among the families. Results indicated that CHS genes in angiosperm plants were greatly diverse in terms of copy number, base substitution rate, and duplication/deletion events, which might be correlated with the diversity of life history, habitat, floral characters, and defense system of angiosperm plants.

Key words: Lunularia cruciata , chalcone synthase, phylogeny, substitution rate