Study reveals the gene responsible for diverse color patterns in African violets

Flowers, specialized plant structures consisting of colorful petals and green sepals, play a key role in plant propagation. In addition to their ornamental value, flowers have gained emotional and cultural significance over the years. The African violet, scientifically known as Streptocarpus sect. Saintpaulia ionanthus Wendl., is a remarkable ornamental plant with unique color patterns in its flowers due to the accumulation of anthocyanins—a chemical substance that imparts different colors.

Among the diverse varieties of Saintpaulia flowers, the white-striped petal variety has been exclusively bred for its aesthetic appeal and horticultural value.

Until recently, scientists believed that the white-striped Saintpaulia flowers were a result of periclinal chimera—genetically distinct cell layers that give rise to different colors. However, recent studies involving chrysanthemum flowers suggest that a specific gene called MYB was responsible for floral color variation.

To identify the underlying mechanisms driving pigment accumulation and pattern formation in the petals of Saintpaulia flowers, a team of scientists led by Professor Munetaka Hosokawa from the Graduate School of Agriculture, Kindai University, Japan, including Dr. Daichi Kurata, also from the same university, conducted a new study.

The researchers hypothesized that the white-striped petal pattern was due to selective gene regulation rather than periclinal chimera, and they carried out an in-depth gene expression analysis and epigenomic profiling. Their research findings were published in the New Phytologist.

“Just as domestication in crops has led to the selection of specific genes, I became interested in uncovering which traits humans have favored in ornamental flowers,” says Prof. Hosokawa. “To conduct such studies, a suitable model plant is necessary, and we have continued our experiments with the belief that Saintpaulia could serve as a good model species.”

Initially, the researchers employed plant tissue culture techniques to obtain Saintpaulia plants with either pink petals or white petals or white-striped petals. During analysis of the phenotypes in regenerated plants, they observed variations in anthocyanin accumulation, resulting in random pigmentation and color. Furthermore, several flavonoid-based biomolecules enriched in the pink petal variety were present at very low quantities in the white petal plants.

Advanced genome sequencing analysis revealed that important anthocyanin biosynthesis genes (ABGs) were suppressed in white petals. To identify the key regulator that was responsible for ABG suppression, the researchers turned their attention to quantitative reverse transcription-polymerase chain reaction—an experimental technique to quantify gene expression levels—and molecular phylogenetic tree analysis. The results revealed that the SiMYB2 gene and SibHLH2 are the genes that could be involved in the unstable pigmentation of Saintpaulia petals.

By carefully analyzing the methylation levels of the two genes, they identified SiMYB2 as the specific gene associated with unstable pigment accumulation. Genomic mapping of the SiMYB2 gene revealed that it produces two distinct mRNA transcripts called SiMYB2-Long and SiMYB2-Short. Notably, SiMYB2-Long was expressed in colored tissues, while SiMYB2-Short was expressed only in noncolored tissues.

Taken together, this study identifies the gene responsible for the variation in Saintpaulia phenotype that changes during tissue culture-based propagation.

Prof. Hosokawa states, “Humans have long created many flower cultivars by making use of mutations. Research on floral patterns, however, is still in its early stages, and we are just beginning to understand how these patterns arise. In the next five to 10 years, the genetic basis of flower patterning may become clearer, potentially enabling more deliberate breeding of patterned flowers.”