Fig. 4.

Schematics of diverse flower symmetries and their developmental patterns. (A) Schematics showing different types of flower symmetry patterns, where dashed lines represent the axes of symmetry. (B-F) Schematics illustrating how flower symmetry develops in different species. Flower diagrams show sepals, petals, stamens and carpels from the outside-in. Gene expression patterns are superimposed on the diagrams of the developing flowers for which expression data are available; black represents CYC-like gene expression, red represents RADIALIS gene expression and blue represents DIVARICATA gene expression. (B) During flower symmetry development of Antirrhinum majus, CYC2 genes and their target RAD are spatially restricted to the dorsal region of the flower, inhibiting DIV activity in the dorsal region and leading to dorsal petal identity and an aborted dorsal stamen. (C) In New World Malpighiaceae zygomorphic flowers, there is a 36-degree rotation from the incipient axis of symmetry (dashed line) to the final axis of symmetry (solid line) during development, which is likely regulated by the dorsal restriction of CYC2 genes, and particularly the expression of BaCYC2B in one of the two dorsal petals. This leads to the formation of the banner petal and the rotation of the axis of symmetry. (D) Schematics show Solanaceae floral phyllotaxis and symmetry patterns, including actinomorphic Nicotiana (white), zygomorphic Browallia (dark purple) and the actinomorphic corolla with zygomorphic stamens of Mandragora (light purple). Little is known about the underlying mechanisms leading to these alternate symmetry patterns between organ whorls of Solanaceae flowers. (E) Expression of CYC-like genes superimposed on floral diagrams of external and internal florets of Knautia (Dipsacaceae). Differences in the expression of CYC-like genes in the ventral region lead to differences in morphology between the florets. (F) Expression of CYC-like genes superimposed on floral diagrams of disc and ray florets of Asteraceae. In actinomorphic disk florets, the expression of the CYC-like genes is the same (either present or absent) across all petals, whereas in zygomorphic ray florets it is differential between dorsal and ventral petals.