The Role of Floral Symmetry Genes on Actinomorphic Reversion in Domesticated Saintpaulia ionantha

Flower symmetry switching from actinomorphy to zygomorphy is an important evolution trait in angiosperm. Zygomorphic flowering species often attract specific pollinators with greater pollination efficiency, therefore, these species usually have higher speciation rate. However, among zygomorphic Gesneriaceae species, some species have evolved from zygomorphy back to actinomorphy. In Saintpaulia ionantha (African violet, Gesneriaceae), actinomorphic peloria was raised in domesticated cultivation from the zygomorphic wild type. By comparing flower development between zygomorphic wild type and actinomorphic peloric type, the genetic differences can be identified. In model plant, Antirrhinum majus, CYCLOIDEA (CYC) and DICHOTOMA (DICH) have been shown expressed in dorsal petals and co-activate RADIALIS (RAD). On the other hand, DIVARICATA (DIV) expresses in ventral petals and antagonize with RAD to generate zygomorphy. Expression patterns of these Saintpaulia homologs (SiCYC, SiRAD, and SiDIV) thus were compared between flower buds of zygomorphic wild type and actinomorphic peloria. The results showed that, SiCYC1A and SiCYC1B were both detected in dorsal petals of wild type and peloria at early bud stage (3mm in diameter) but not in later stage (30 mm in diameter). On the other hand, SiDIV persists to express along late flowering stages in peloria but not in wild type. This suggests persistent expression of SiDIV and ceasing of SiCYC1A and SiCYC1B in late peloric flower stage may generate the actinomorphic flower (ventralized effect). Moreover, the expression of SiCYC in dorsal part of flowers in peloria may explain why the peloria retains traced zygomorphic syndrome (the dorsal and lateral stamens are smaller than the ventral ones). This is the first report that not only the differences of flower symmetry genes expression but also expression timings may result to zygomorphy/actinomorphy transition.