Anthocyanin Pigmentation Controlled by speckled and c-1 Mutations of Japanese Morning Glory

Abstract

Anthocyanin pigments and their related compounds were examined in the flowers of F1 and F2 plants generated by crosses between two acyanic lines, 54Y having a speckled mutation for pale yellow flowers and 78WWc-1 carrying the c-1 mutation conferring white flowers, in Japanese morning glory. The mutable speckled allele generates speckled flowers when a dominant genetic element, speckled-activator, is present in its genome. The Speckled and C-1 loci are tightly linked, and 78WWc-1, but not 54Y, bears the specked-activator. The flower color of F1 progeny is red-purple, and F2 population displays a ratio of 8 red-purple flowers: 4 white flowers: 3 speckled flowers with red-purple spots pale-yellow background: 1 pale-yellow flower. The anthocyanin components of red-purple flowers in F1 and F2 plants as well as red-purple spots of the speckled flower in the F2 generation were identical. Wedding Bells Anthocyanin (WBA) was accumulated in red-purple flowers as the dominant anthocyanin along with its precursor, pelargonidin 3-sophoroside-5-glucoside, and eight of its acylated derivatives as minor anthocyanins. The major flavonoid pigment in the pale-yellow flowers of 54Y and the F2 plants as well as the pale-yellow background of the speckled flower in the F2 generation was identified as chalcononaringenin 2'-glucoside by chemical and spectroscopic methods. Furthermore, chlorogenic acid and small amounts of caffeic acid as well as aureusidin 4-glucoside were obtained from the pale-yellow flowers. Chlorogenic acid and caffeic acid were also detected in the white flowers of F2 and 78WWc-1. These results suggest that anthocyanin biosynthesis in speckled and c1 mutants stopped at the steps mediated by chalcone isomerase (CHI) and chalcone synthase (CHS), respectively, and that anthocyanin biosynthesis was completely recovered in the red-purple tissue parts of the speckled flower. Moreover, we found that anthocyanin composition varied, especially in the red-purple flowers and red-purple tissue parts in the speckled flowers of F2 plants, implying that WBA biosynthesis depends on unknown genetic backgrounds.