State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
Mol Biol Evol. 2010 Jul;27(7):1598-611. doi: 10.1093/molbev/msq044. Epub 2010 Feb 10.
Floral MADS-box genes encode transcription factors that play critical roles in the development and evolution of the flower. Proteins of floral MADS-box genes regulate the expression of their downstream genes by forming various homodimers/heterodimers and quaternary complexes. Interactions among proteins of floral MADS-box genes have been documented in several model species, yet the information accumulated so far is still not sufficient to draw a general picture of the evolution of the interactions. We have characterized 28 putative floral MADS-box genes from three representative basal eudicots (i.e., Euptelea pleiospermum, Akebia trifoliata, and Pachysandra terminalis) and investigated the protein-protein interactions (PPIs) among the proteins encoded by these genes using yeast two-hybrid assays. We found that, although the PPIs in basal eudicots are largely consistent with those in core eudicots and monocots, there are lineage-specific features that have not been observed elsewhere. We also reconstructed the evolutionary histories of the PPIs among members of seven MADS-box gene lineages (i.e., AP1, AP3, PI, AG, STK, AGL2, and AGL9) in angiosperms. We revealed that the PPIs were extremely conserved in nine (or 32.1%) of the 28 possible combinations, whereas considerable variations existed in seven (25.0%) of them; in the remaining 12 (or 42.9%) combinations, however, no interaction was observed. Notably, most of the PPIs required for the formation of quaternary complexes, as suggested by the "quartet model," were highly conserved. This suggested that the evolutionarily conservative PPIs may have played critical roles in the establishment of the basic structure (or architecture) of the flower and experienced coevolution to maintain their functions. The evolutionarily variable PPIs, however, seem to have played subsidiary roles in flower development and have contributed to the variation in floral traits.
花器官 MADS-box 基因编码的转录因子在花的发育和进化中起着关键作用。花器官 MADS-box 基因的蛋白质通过形成各种同源二聚体/异源二聚体和四聚体复合物来调节其下游基因的表达。在几个模式物种中已经记录了花器官 MADS-box 基因的蛋白质之间的相互作用，但迄今为止积累的信息还不足以描绘相互作用进化的总体情况。我们从三个代表性的基干真双子叶植物（即 Euptelea pleiospermum、Akebia trifoliata 和 Pachysandra terminalis）中鉴定了 28 个假定的花器官 MADS-box 基因，并使用酵母双杂交试验研究了这些基因编码的蛋白质之间的蛋白质-蛋白质相互作用（PPIs）。我们发现，尽管基干真双子叶植物的 PPIs 在很大程度上与核心真双子叶植物和单子叶植物的 PPIs 一致，但也存在其他地方没有观察到的谱系特异性特征。我们还重建了 7 个 MADS-box 基因谱系（即 AP1、AP3、PI、AG、STK、AGL2 和 AGL9）成员之间的 PPIs 的进化历史。我们揭示了在 28 个可能的组合中的 9 个（或 32.1%）中，PPIs 是极其保守的，而在其中的 7 个（25.0%）中存在相当大的变异；然而，在其余的 12 个（或 42.9%）组合中，没有观察到相互作用。值得注意的是，正如“ Quartet 模型”所建议的，形成四聚体复合物所需的大多数 PPIs 高度保守。这表明进化保守的 PPIs 可能在花的基本结构（或架构）的建立中发挥了关键作用，并经历了共同进化以维持其功能。然而，进化上可变的 PPIs 似乎在花发育中发挥了辅助作用，并促进了花特征的变异。
