title: Duplication and functional divergence in the chalcone synthase gene family of Asteraceae: evolution with substrate change and catalytic simplification.
abstract: Plant-specific polyketide synthase genes constitute a gene superfamily, including universal chalcone synthase [CHS; malonyl-CoA:4-coumaroyl-CoA malonyltransferase (cyclizing) (EC 2.3.1.74)] genes, sporadically distributed stilbene synthase (SS) genes, and atypical, as-yet-uncharacterized CHS-like genes. We have recently isolated from Gerbera hybrida (Asteraceae) an unusual CHS-like gene, GCHS2, which codes for an enzyme with structural and enzymatic properties as well as ontogenetic distribution distinct from both CHS and SS. Here, we show that the GCHS2-like function is encoded in the Gerbera genome by a family of at least three transcriptionally active genes. Conservation within the GCHS2 family was exploited with selective PCR to study the occurrence of GCHS2-like genes in other Asteraceae. Parsimony analysis of the amplified sequences together with CHS-like genes isolated from other taxa of angiosperm subclass Asteridae suggests that GCHS2 has evolved from CHS via a gene duplication event that occurred before the diversification of the Asteraceae. Enzyme activity analysis of proteins produced in vitro indicates that the GCHS2 reaction is a non-SS variant of the CHS reaction, with both different substrate specificity (to benzoyl-CoA) and a truncated catalytic profile. Together with the recent results of Durbin et al. [Durbin, M. L., Learn, G. H., Jr., Huttley, G. A. & Clegg, M. T. (1995) Proc. Natl. Acad. Sci. USA 92, 3338-3342], our study confirms a gene duplication-based model that explains how various related functions have arisen from CHS during plant evolution.
authors.affiliation: Institute of Biotechnology, University of Helsinki, Finland.
authors.forename: Y
authors.initials: Y
authors.lastname: Helariutta
authors.forename: M
authors.initials: M
authors.lastname: Kotilainen
authors.forename: P
authors.initials: P
authors.lastname: Elomaa
authors.forename: N
authors.initials: N
authors.lastname: Kalkkinen
authors.forename: K
authors.initials: K
authors.lastname: Bremer
authors.forename: T H
authors.initials: TH
authors.lastname: Teeri
authors.forename: V A
authors.initials: VA
authors.lastname: Albert
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D000217:Acyltransferases / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D005075:Biological Evolution; D018076:DNA, Complementary / Q000235:genetics; D015723:Gene Library; D017343:Genes, Plant; D008316:Malonyl Coenzyme A / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D010944:Plants / Q000201:enzymology / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013379:Substrate Specificity
chemical_list: D000214:Acyl Coenzyme A; D018076:DNA, Complementary; C058644:4-coumaroyl-coenzyme A; D008316:Malonyl Coenzyme A; D000217:Acyltransferases; C020141:flavanone synthetase