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.