A Torenia Mutant Bearing Shrunken Reddish-purple Flower and its Potential for Breeding

Abstract

A torenia mutant, designated as “reddish purple shrunken” (RPS) because of its shrunken reddish-purple petals, was isolated from the S₁ progeny of a “flecked” mutant containing an active DNA transposon Ttf1. Cyanidin-type anthocyanins—i.e., peonidin 3,5-diglucoside and cyanidin 3,5-diglucoside—were detected in petals of the RPS mutant, whereas delphinidin-type anthocyanins—i.e., malvidin 3,5-diglucoside, petunidin 3,5-diglucoside, and delphinidin 3,5-diglucoside—were the major anthocyanins in normal-type petals. Petal shrinkage could be attributed to this change in anthocyanin composition. A frameshift mutation in the first exon of flavonoid 3',5'-hydroxylase (TfF3'5'H^ΔC) inhibited biosynthesis of delphinidin-type anthocyanins in RPS. The “white” (W) mutant bore pure white petals in response to Ttf1 insertion in the first exon of the flavanone 3-hydroxylase gene (TfF3H^Ttf1). Some F₂ plants derived from the cross between RPS and W bore reddish-purple petals without any shrinkage; these were designated as “reddish purple” (RP). This RP genotype was revealed as a heterozygote of TfF3H⁺ and TfF3H^Ttf1 in the background of the TfF3'5'H^ΔC homozygote. A gene dosage effect of TfF3H reduced anthocyanin biosynthesis in RP compared with RPS, whereas this decrease caused no reduction in visual color density. Therefore, a partial decrease in anthocyanin biosynthesis may be beneficial if petal shrinkage prevents using a new-color mutant for breeding.