Specific Duplication and Dorsoventrally Asymmetric Expression Patterns of Cycloidea-Like Genes in Zygomorphic Species of Ranunculaceae

Floral bilateral symmetry (zygomorphy) has evolved several times independently in angiosperms from radially symmetrical (actinomorphic) ancestral states. Homologs of the Antirrhinum majus Cycloidea gene (Cyc) have been shown to control floral symmetry in diverse groups in core eudicots. In the basal eudicot family Ranunculaceae, there is a single evolutionary transition from actinomorphy to zygomorphy in the stem lineage of the tribe Delphinieae. We characterized Cyc homologs in 18 genera of Ranunculaceae, including the four genera of Delphinieae, in a sampling that represents the floral morphological diversity of this tribe, and reconstructed the evolutionary history of this gene family in Ranunculaceae. Within each of the two RanaCyL (Ranunculaceae Cycloidea-like) lineages previously identified, an additional duplication possibly predating the emergence of the Delphinieae was found, resulting in up to four gene copies in zygomorphic species. Expression analyses indicate that the RanaCyL paralogs are expressed early in floral buds and that the duration of their expression varies between species and paralog class. At most one RanaCyL paralog was expressed during the late stages of floral development in the actinomorphic species studied whereas all paralogs from the zygomorphic species were expressed, composing a species-specific identity code for perianth organs. The contrasted asymmetric patterns of expression observed in the two zygomorphic species is discussed in relation to their distinct perianth architecture.花两侧对称（zygomorphy）已在被子植物中多次从辐射对称（actinomorphy）的祖先状态独立演化而来。金鱼草（Antirrhinum majus）的Cycloidea基因（Cyc）同源基因已被证实可调控核心真双子叶植物不同类群的花对称性。在基部真双子叶植物类群毛茛科（Ranunculaceae）中，翠雀族的茎谱系仅发生过一次从辐射对称到两侧对称的演化转变。我们对覆盖翠雀族花形态多样性的采样样本中的毛茛科18个属（含该族4个属）的Cyc同源基因进行了表征，并重构了该基因家族在毛茛科中的演化历史。在先前鉴定出的两个RanaCyL（Ranunculaceae Cycloidea-like）谱系中，均发现了一次可能早于翠雀族起源的额外基因复制事件，使得两侧对称物种中最多可存在4个基因拷贝。表达分析结果表明，RanaCyL旁系同源基因在花芽发育早期即有表达，且其表达时长因物种及旁系同源类群而异。在所研究的辐射对称物种中，花发育后期最多仅有一种RanaCyL旁系同源基因得以表达；而两侧对称物种的所有旁系同源基因均有表达，这构成了花被器官的物种特异性身份编码。本文针对两种两侧对称物种中观察到的对比鲜明的不对称表达模式，结合其独特的花被结构展开了相关讨论。