Abstract：Diversity of branching types is produced during the evolution of Asteraceae, which is originated by the diversity of branching genes. BRC1 (BRANCHED1) genes, as the member of TCP family, are proved to play important roles in inhibition of lateral branches. BRC1-like genes were replicated during evolution, and different members were through different selective pressures, both of which may lead to the large family and diverse functions. Twenty-one BRC1-like gene fragments were isolated from 16 Asteraceae species, which contained the conserved TCP domain, R domain and ECE motif, and were in the CYCLOIDEA1 (CYC1) subclade of TCP family. With the sequences we cloned and sequences from gerbera (Gerbera hybrid) and sunflower (Helianthus annuus)(downloaded from NCBI), phylogenetic tree were constructed. All the BRC1-like genes from Asteraceae were clustered into two groups, BRC1a and BRC1b, which indicated that CYC1 subclade replicated and expanded during evolution. Maximum likelihood (ML) branch test was performed to detect the selective pressure, the results indicated that BRC1b group evoloved under a strong purifying selection, while the BRC1a group had experienced a decrease in evolutionary constrains. Results in the ML branch-site test showed that, relaxation of selective constrains rather than positive selection was the process associated with the evolution of BRC1a group. The amino acid residue targets of selection in all BRC1-like genes were identified with ML site test model. The results indicated that, residues evolved under strong purifying selections were located in the TCP domain, R domain and ECE motif, inferred that important domains were fixed during evolution. The evolution of BRC1-like gene in Asteraceae indicates that two groups were clustered through replication, then these two groups underwent different selective pressures, which may lead to different functions of genes.
