Kostyun Jamie L, Robertson Josephine E, Preston Jill C
Department of Plant Biology, The University of Vermont, 111 Jeffords Hall, 63 Carrigan Drive, Burlington, VT 05405 USA.
Evodevo. 2019 Apr 19;10:9. doi: 10.1186/s13227-019-0122-9. eCollection 2019.
Understanding the evolution of novel features requires homology assessments at different levels of biological organization. In flowering plants, floral coronas that play various roles in plant-pollinator interactions have evolved multiple times independently, but are highly variable in their final position and overall morphology. Coronas of the Solanaceae species are found between the corolla and stamens, adjacent to the gynoecium, and form cups that house copious amounts of their characteristic blood red nectar. To test the hypothesis that coronas evolved as an outgrowth of stamens and therefore have staminal identity, we assessed their development, floral organ identity gene expression, and cellular morphology.
coronas emerge after the initiation of all conventional floral organs on the abaxial side of the proximally modified stamens and then expand medially and laterally to form nectar cups. Overlapping expression of the B-class organ identity genes and both orthologs ( and ), and the C-class-like gene -like, unites the stamens and corona. Epidermal cell shape also connects the adaxial surface of coronas and petals, and the stamen base, with remaining floral organs showing divergent cell types.
Our data, based on multiple lines of evidence, support a largely staminal origin for coronas. However, since slightly enlarged stamen bases are found in species that lack coronas, and stamen bases share cell types with petals, we hypothesize that stamen bases recruited part of the petal identity program prior to fully expanding into a corona.
理解新特征的进化需要在生物组织的不同层面进行同源性评估。在开花植物中，在植物与传粉者相互作用中发挥各种作用的花副冠已经多次独立进化，但其最终位置和整体形态变化很大。茄科植物的副冠位于花冠和雄蕊之间，与雌蕊相邻，形成容纳大量其特有的血红色花蜜的杯状结构。为了验证副冠是作为雄蕊的突出物进化而来，因此具有雄蕊身份的假说，我们评估了它们的发育、花器官身份基因表达和细胞形态。
副冠在近端经过修饰的雄蕊的远轴侧所有传统花器官起始之后出现，然后向内侧和外侧扩展形成花蜜杯。B类器官身份基因及其两个直系同源基因（和）以及C类样基因-like的重叠表达将雄蕊和副冠联系在一起。表皮细胞形状也将副冠和花瓣的近轴表面以及雄蕊基部与其余花器官连接起来，其余花器官显示出不同的细胞类型。
我们基于多条证据的数据支持副冠主要起源于雄蕊。然而，由于在没有副冠的物种中发现雄蕊基部略有增大，并且雄蕊基部与花瓣共享细胞类型，我们推测雄蕊基部在完全扩展成副冠之前招募了部分花瓣身份程序。
