Ruelens Philip, Zhang Zhicheng, van Mourik Hilda, Maere Steven, Kaufmann Kerstin, Geuten Koen
Department of Biology, KU Leuven, B-3001 Leuven, Belgium.
Laboratory of Molecular Biology, Wageningen University, 6708PB Wageningen, The Netherlands.
Plant Cell. 2017 Feb;29(2):229-242. doi: 10.1105/tpc.16.00366. Epub 2017 Jan 18.
The origin of flowers has puzzled plant biologists ever since Darwin referred to their sudden appearance in the fossil record as an abominable mystery. Flowers are considered to be an assembly of protective, attractive, and reproductive male and female leaf-like organs. Their origin cannot be understood by a morphological comparison to gymnosperms, their closest relatives, which develop separate male or female cones. Despite these morphological differences, gymnosperms and angiosperms possess a similar genetic toolbox consisting of phylogenetically related MADS domain proteins. Using ancestral MADS domain protein reconstruction, we trace the evolution of organ identity quartets along the stem lineage of crown angiosperms. We provide evidence that current floral quartets specifying male organ identity, which consist of four types of subunits, evolved from ancestral complexes of two types of subunits through gene duplication and integration of SEPALLATA proteins just before the origin of flowering plants. Our results suggest that protein interaction changes underlying this compositional shift were the result of a gradual and reversible evolutionary trajectory. Modeling shows that such compositional changes may have facilitated the evolution of the perfect, bisexual flower.
自从达尔文将花朵在化石记录中的突然出现称为“可恶的谜团”以来，花朵的起源一直困扰着植物生物学家。花朵被认为是由具有保护、吸引和繁殖功能的雄性和雌性叶状器官组成的集合体。通过与裸子植物（它们最亲近的亲属，裸子植物产生单独的雄性或雌性球果）进行形态学比较，无法理解花朵的起源。尽管存在这些形态学差异，但裸子植物和被子植物拥有一个由系统发育相关的MADS结构域蛋白组成的类似遗传工具箱。利用祖先MADS结构域蛋白重建，我们沿着冠层被子植物的茎系追溯器官身份四重奏的进化。我们提供的证据表明，目前指定雄性器官身份的花四重奏由四种类型的亚基组成，它是在开花植物起源之前通过基因复制和SEPALLATA蛋白的整合，从两种类型亚基的祖先复合体进化而来的。我们的结果表明，这种组成变化背后的蛋白质相互作用变化是一个渐进且可逆的进化轨迹的结果。模型显示，这种组成变化可能促进了完美两性花的进化。
