Interaction between the Tam1 and Tam2 transposable elements of Antirrhinum majus

Summary Two stable derivatives of the highly unstable niv-53::Tam1 allele of Antirrhinum majus were analysed. In both derivatives the Tam1 element is integrated at the same site and in the same orientation as in the parental niv-53::Tam1 allele. In both cases the Tam1 element was found to carry a 5 bp deletion (CACTA) in one of its termini. This explains the excision deficiency of these two alleles of Tam1, niv-53::Tam1-46 and niv-53::Tam1-49. Niv-44::Tam2, another stable nivea mutation, carries the 5 kb element Tam2, which is not a derivative of Tam1 but possesses identical terminal inverted repeats. When the stable lines 46 and 49 were corssed with line 44, suprisingly, a high number of the flowers in the F₁ displayed a variegated phenotype. Sequence analysis of two germinal revertants isolated from the heterozygote niv-53::Tam1-46/niv-44::Tam2 shows excision of the Tam2 element. This indicates that Tam2 is a defective element, which can be complemented by an active Tam1 element. However, the variegated F₁ phenotype observed is not inherited monofactorially. Variegation is seen only at particular times of development of the F₁ plants. These phenomena seem to involve both the Tam1 and Tam2 transposable elements.