title: Tandemly arranged chalcone synthase A genes contribute to the spatially regulated expression of siRNA and the natural bicolor floral phenotype in Petunia hybrida.
abstract: The natural bicolor floral traits of the horticultural petunia (Petunia hybrida) cultivars Picotee and Star are caused by the spatial repression of the chalcone synthase A (CHS-A) gene, which encodes an anthocyanin biosynthetic enzyme. Here we show that Picotee and Star petunias carry the same short interfering RNA (siRNA)-producing locus, consisting of two intact CHS-A copies, PhCHS-A1 and PhCHS-A2, in a tandem head-to-tail orientation. The precursor CHS mRNAs are transcribed from the two CHS-A copies throughout the bicolored petals, but the mature CHS mRNAs are not found in the white tissues. An analysis of small RNAs revealed the accumulation of siRNAs of 21 nucleotides that originated from the exon 2 region of both CHS-A copies. This accumulation is closely correlated with the disappearance of the CHS mRNAs, indicating that the bicolor floral phenotype is caused by the spatially regulated post-transcriptional silencing of both CHS-A genes. Linkage between the tandemly arranged CHS-A allele and the bicolor floral trait indicates that the CHS-A allele is a necessary factor to confer the trait. We suppose that the spatially regulated production of siRNAs in Picotee and Star flowers is triggered by another putative regulatory locus, and that the silencing mechanism in this case may be different from other known mechanisms of post-transcriptional gene silencing in plants. A sequence analysis of wild Petunia species indicated that these tandem CHS-A genes originated from Petunia integrifolia and/or Petunia inflata, the parental species of P. hybrida, as a result of a chromosomal rearrangement rather than a gene duplication event.
authors.affiliation: Institute of Floricultural Science, National Agriculture and Food Research Organization, Tsukuba 305-8519, Japan.
authors.forename: Yasumasa
authors.initials: Y
authors.lastname: Morita
authors.forename: Ryoko
authors.initials: R
authors.lastname: Saito
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Ban
authors.forename: Natsu
authors.initials: N
authors.lastname: Tanikawa
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Kuchitsu
authors.forename: Toshio
authors.initials: T
authors.lastname: Ando
authors.forename: Manabu
authors.initials: M
authors.lastname: Yoshikawa
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Habu
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ozeki
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakayama
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D035264:Flowers / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018628:Gene Dosage; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D056426:Genetic Loci; D008969:Molecular Sequence Data; D032306:Petunia / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism*; D050436:Regulatory Elements, Transcriptional; D013045:Species Specificity; D020080:Tandem Repeat Sequences
chemical_list: D010940:Plant Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D000217:Acyltransferases; C020141:flavanone synthetase