Transposon - lnduced lnversion in Antirrhinum Modifies niwea Gene Expression To Give a Nove 1 Flower Color Pattern under the Control of cycloídea radialis

The nivea (niv) gene of Antirrhinum majus encodes chalcone synthase, an enzyme involved in synthesis of anthocyanin pigments. The nivfeC:98 allele contains a single copy of the transposon Tamd inserted at the niv locus. A large chromosomal rearrangement derived from this mutant has been shown to be flanked by two copies of Tam3. In this study, we compared sequences involved in this rearrangement with their progenitor sequences and concluded that the rearrangement is an inversion resulting from an aberrant transposition occurring shortly after replication of Tam3 that left both copies of Tam3 active after the rearrangement. Excision of Tam3 from its position adjacent to the niv coding region resulted in a novel distribution of anthocyanin pigment in the flower tube, caused by the interaction of the new sequences with the remnant of the niw promoter. The new sequences upstream of niv serve both to enhance niv transcription and to redirect the pattern of gene expression, placing niw under the control of the gene cycloideafad'afls, which determines the morphogenetic polarity of the flower.