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

## TL;DR

African violets' unstable flower color is caused by a single MYB gene, SiMYB2, which produces two RNA variants that control pigment production through epigenetic regulation.

## Contribution

Discovery that unstable pigmentation in African violets is due to transcriptional selectivity of a single MYB gene, SiMYB2, and its epigenetic regulation.

## Key findings

- SiMYB2 generates two RNA variants, SiMYB2-Long and SiMYB2-Short, with distinct tissue-specific expression.
- SiMYB2-Long activates anthocyanin biosynthesis in colored tissues, while SiMYB2-Short is nonfunctional in noncolored tissues.
- A transposon-like insertion in Exon 3 of SiMYB2 correlates with pigment variation and increased anthocyanin content in mutants.

## Abstract

Saintpaulia (African violet) pigmentation is notoriously unstable and sometimes forms white stripes, particularly following passage through tissue culture. White‐striped petals were thought to be due to periclinal chimeras, but we confirmed that white stripes result from epigenetic regulation rather than periclinal chimeras based on the flower color traits of plants obtained from tissue culture.Gene 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 noncolored tissues. Functional analyses revealed that SiMYB2‐Long is an anthocyanin biosynthesis activator and SiMYB2‐Short is nonfunctional. Exon 3 of SiMYB2 was generated by the insertion of a transposon‐like sequence. A mutant lacking the element was obtained from cultivars with noncolored tissues. Anthocyanin content and SiMYB2‐Long expression in the mutant were greatly increased compared to wild‐type.Our results suggest that the white‐striped petals of Saintpaulia are not formed by periclinal chimeras but through the transcriptional selectivity of epigenetically regulated SiMYB2.

Saintpaulia (African violet) pigmentation is notoriously unstable and sometimes forms white stripes, particularly following passage through tissue culture. White‐striped petals were thought to be due to periclinal chimeras, but we confirmed that white stripes result from epigenetic regulation rather than periclinal chimeras based on the flower color traits of plants obtained from tissue culture.

Gene 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 noncolored tissues. Functional analyses revealed that SiMYB2‐Long is an anthocyanin biosynthesis activator and SiMYB2‐Short is nonfunctional. Exon 3 of SiMYB2 was generated by the insertion of a transposon‐like sequence. A mutant lacking the element was obtained from cultivars with noncolored tissues. Anthocyanin content and SiMYB2‐Long expression in the mutant were greatly increased compared to wild‐type.

Our results suggest that the white‐striped petals of Saintpaulia are not formed by periclinal chimeras but through the transcriptional selectivity of epigenetically regulated SiMYB2.