Dynamics of mobile element activity in chalcone synthase loci in the common morning glory (Ipomoea purpurea)

Mobile element dynamics in seven alleles of the chalcone synthase D locus (CHS-D) of the common morning glory (Ipomoea purpurea) are analyzed in the context of synonymous nucleotide sequence distances for CHS-D exons. By using a nucleotide sequence of CHS-D from the sister species Ipomoea nil (Japanese morning glory [Johzuka-Hisatomi, Y., Hoshino, A., Mori, T., Habu, Y. & Iida, S. (1999) Genes Genet. Syst. 74, 141–147], it is also possible to determine the relative frequency of insertion and loss of elements within the CHS-D locus between these two species. At least four different types of transposable elements exist upstream of the coding region, or within the single intron of the CHS-D locus in I. purpurea. There are three distinct families of miniature inverted-repeat transposable elements (MITES), and some recent transpositions of Activator/Dissociation (Ac/Ds)-like elements (Tip100), of some short interspersed repetitive elements (SINEs), and of an insertion sequence (InsIpCHSD) found in the neighborhood of this locus. The data provide no compelling evidence of the transposition of the mites since the separation of I. nil and I. purpurea roughly 8 million years ago. Finally, it is shown that the number and frequency of mobile elements are highly heterogeneous among different duplicate CHS loci, suggesting that the dynamics observed at CHS-D are locus-specific.

Evolution of the chalcone synthase gene family in the genus Ipomoea.

The evolution of the chalcone synthase [CHS; malonyl-CoA:4-coumaroyl-CoA malonyltransferase (cyclizing), EC 2.3.1.74] multigene family in the genus Ipomoea is explored. Thirteen CHS genes from seven Ipomoea species (family Convolvulaceae) were sequenced--three from genomic clones and the remainder from PCR amplification with primers designed from the 5' flanking region and the end of the 3' coding region of Ipomoea purpurea Roth. Analysis of the data indicates a duplication of CHS that predates the divergence of the Ipomoea species in this study. The Ipomoea CHS genes are among the most rapidly evolving of the CHS genes sequenced to date. The CHS genes in this study are most closely related to the Petunia CHS-B gene, which is also rapidly evolving and highly divergent from the rest of the Petunia CHS sequences.