Unstable anthocyanin pigmentation in Streptocarpus sect. Saintpaulia (African violet) is due to transcriptional selectivity of a single MYB gene

O_LISaintpaulia (African violet) pigmentation is notoriously unstable, particularly following passage through tissue culture, but the instability mechanism is unknown. White-striped petals were thought to be due to epigenetics, but the genes involved are unknown. We confirmed that white stripes result from epigenetic regulation based on the flower color traits of plants obtained from tissue culture. C_LIO_LIGene expression in several plant lines, anthocyanin quantification, bisulfite sequencing, and methylation analyses were used to demonstrate the presence of a single MYB gene responsible for pigment variation. We identified SiMYB2 as the cause of variations in tissue color patterning, and that two RNAs were generated from SiMYB2. SiMYB2-Long was expressed in colored tissues, while SiMYB2-Short was expressed only in non-colored tissues. Functional analyses revealed that SiMYB2-Long is an anthocyanin biosynthesis activator and SiMYB2-Short is non-functional. Exon 3 of SiMYB2 was generated by the insertion of a transposon-like sequence. A mutant lacking the element was obtained from cultivars with non-colored tissues. Anthocyanin content and SiMYB2-Long expression in the mutant were greatly increased compared to wild type. C_LIO_LIOur results suggest that the white-striped petals of Saintpaulia are not formed by periclinal chimeras but thorough the transcriptional selectivity of epigenetically regulated SiMYB2. C_LI