Genetic regulation of SaCYC on floral symmetry in domesticated African violet

Floral bilateral symmetry (zygomorphy) is a major evolutionary trend in creating floral diversity. Wild-type African violet (Saintpaulia ionantha) flower is bilateral symmetry with two smaller dorsal petals and three larger ventral petals. The two radial symmetry cultivars, one with 5 dorsalized petals and the other one with 5 ventralized petals, have been artificially selected. Previous research indicated that CYCLOIDEA-like genes (SaCYCs) have been shown a dorsal-specific expression in the zygomorphic wild-type flower, while a reduced expression in the ventralized flower and an expanded expression in entire dorsalized flower, implying the alteration of the spatial expression pattern of SaCYCs might contribute to the transition of floral symmetry among cultivars. The aims, therefore, are to examine the genetic regulation on SaCYCs by analyzing the association between SaCYC allele and floral symmetry and understand the functions of SaCYC in floral symmetry development. Here, crossing between the zygomorphic wild-type and the ventralized cultivar gave all F1 zygomorphy, suggesting the wild-type is homozygous dominant (SaCYCW/SaCYCW), while the ventralized cultivar is homozygous recessive (SaCYCV/SaCYCV). Overexpression of SaCYC1AW and SaCYC1AV in Arabidopsis both showed smaller petals, curled leaves and dwarfism, suggesting coding regions of wild-type and ventralized alleles have similar functions on cell proliferation in floral development. On the other hand, crossing between zygomorphic wild-type and dorsalized cultivar segregated close to a 1:1 ratio in F1 on each parental type, suggesting the dorsalized cultivar is a heterozygote (SaCYCD/SaCYCW) and SaCYCD is dominant to SaCYCW. Although F1 hybrids with dorsalized actinomorphy all have entire flower SaCYC expression, their allelic combinations could be SaCYCD/SaCYCW or SaCYCW/SaCYCW. Surprisingly, those zygomorphic F1 individuals all have SaCYC specifically expressed at dorsal petals, but combinations of these alleles showed no difference as those of dorsalized actinomorphic F1s. This seems to rule out that the differences between cis-regulating elements (promoter regions) of zygomorphic wildtype and dorsalized cultivars are responsible for the variations of spatial SaCYC expression patterns during symmetry transition. To conclude, SaCYC does participate a crucial and indispensable role in the signal transduction pathway for floral symmetry development, but there might be an unidentified upstream factor(s) regulating the spatially specific pattern of SaCYC (trans-regulation), leading to floral symmetry transition among these three cultivars. In the future, using a biolistic bombardment to introduce SaCYC promoters of wildtype and dorsalized cultivars into petals of the actinomorphic cultivar with a GUS reporter transient assay can further support my conclusion. Preliminarily data was found that at target distance 9 cm and helium pressure 900 psi condition appeared better signals. Overall, this study is the first to suggest the unknown upstream controller of SaCYC is also an important missing link for regulating floral symmetry.