4. Conclusion

In this study, we have reported the genome sequence for S. tetraptera . Based on this reference genome, we examined transcriptome differentiation of dimorphic flowers. In addition to MADS-box genes (Yiyang Liu et al., 2021), we revealed more distinctly expressed genes related to open versus closed pollination, nectary development, petal color, and bioactive compounds when comparing CH and CL flowers inS. tetraptera . It should be noted that we first found that the new genes derived from the species-specific WGD may have been involved in the evolution of such an innovative trait. In addition, we found contrasting concentrations of hormones and iridoids and the differential expression of related genes when comparing the two flower types. Therefore, the evolution and development of the aerial dimorphic flowers from numerous unrelated families (Campbell et al. , 1983; Culley and Klooster, 2007) may involve multiple but different genes despite the common ecological role of reproductive assurance in extreme habitats (Koontz et al. , 2017; Ansaldi et al. , 2018). Further genomic studies and comparisons of more species with dimorphic flowers are needed to examine how this innovative trait originated repeatedly in unrelated angiosperms. In addition, we identified candidate genes for iridoid biosynthesis in S. tetrapterae . Our co-expression analyses revealed two hub genes, which may be essential in transferring intermediate products during iridoid biosynthesis between leaves and flowers. This information may be very useful for artificially creating iridoids in cultivated crops in the future.