目的:缺陷(DEF)-和GLOBOSA(GLO)样蛋白构成了两个花同源转录因子的姐妹进化枝,它们已经存在于现存被子植物的最新共同祖先(MRCA)中。它们共同指定开花植物中花瓣和雄蕊的身份。在核心欧元图中,DEF-和GLO-样蛋白在细胞中仅作为彼此的异二聚体起作用。有证据表明,这种专性的异二聚化在进化过程中促成了核心eudicots花结构的渠化。对于这种严格的异二聚体化是否是古老的特征,可以追溯到现存开花植物的MRCA,还是在冠组被子植物的进化过程中后来进化,尚不清楚。
方法:通过使用酵母双杂交分析和电泳迁移率变化分析(EMSA),分析了早期分化的被子植物Amborellatrichopoda和Nupharadvena以及木兰鹅掌子花的DEF和GLO样蛋白的相互作用。字符状态重建,包括其他物种的数据,用于推断DEF-和GLO-样蛋白的祖先相互作用模式。
结果:酵母双杂交和EMSA数据表明,早期分化的被子植物中的DEF-和GLO-样蛋白均为同源二聚化和异源二聚化。特征状态重建表明,在现存的被子植物的MRCA中已经存在形成异二聚体复合物的能力,并且在整个被子植物进化过程中,这种特性仍然高度保守。DEF-和GLO-样蛋白的同二聚化也存在于所有现存被子植物的MRCA中。DEF样蛋白的同源二聚化可能在被子植物进化的早期就丢失了,并且在eudicots和单子叶植物的MRCA中不存在。GLO样蛋白的同源二聚化可能在进化的后期丢失,但很可能不存在于Eudicots的MRCA中。
结论:早期分化的被子植物中DEF和GLO样蛋白相互作用的灵活性可能是在这些物种中观察到高度多样化的花形态的原因之一。结果加强了以下假设:DEF-和GLO-样蛋白的相互作用伴侣数量减少,DEF-GLO异二聚体仍然是核心Eudicots中唯一的DNA结合二聚体,有助于发育的稳健性,花的发育和被子植物的多样化。
OBJECTIVE: DEFICIENS (DEF)- and GLOBOSA (GLO)-like proteins constitute two sister clades of floral homeotic transcription factors that were already present in the most recent common ancestor (MRCA) of extant angiosperms. Together they specify the identity of petals and stamens in flowering plants. In core eudicots, DEF- and GLO-like proteins are functional in the cell only as heterodimers with each other. There is evidence that this obligate heterodimerization contributed to the canalization of the flower structure of core eudicots during evolution. It remains unknown as to whether this strict heterodimerization is an ancient feature that can be traced back to the MRCA of extant flowering plants or if it evolved later during the evolution of the crown group angiosperms.
METHODS: The interactions of DEF- and GLO-like proteins of the early-diverging angiosperms Amborella trichopoda and Nuphar advena and of the magnoliid Liriodendron tulipifera were analysed by employing yeast two-hybrid analysis and electrophoretic mobility shift assay (EMSA). Character-state reconstruction, including data from other species as well, was used to infer the ancestral interaction patterns of DEF- and GLO-like proteins.
RESULTS: The yeast two-hybrid and EMSA data suggest that DEF- and GLO-like proteins from early-diverging angiosperms both homo- and heterodimerize. Character-state reconstruction suggests that the ability to form heterodimeric complexes already existed in the MRCA of extant angiosperms and that this property remained highly conserved throughout angiosperm evolution. Homodimerization of DEF- and GLO-like proteins also existed in the MRCA of all extant angiosperms. DEF-like protein homodimerization was probably lost very early in angiosperm evolution and was not present in the MRCA of eudicots and monocots. GLO-like protein homodimerization might have been lost later during evolution, but very probably was not present in the MRCA of eudicots.
CONCLUSIONS: The flexibility of DEF- and GLO-like protein interactions in early-diverging angiosperms may be one reason for the highly diverse flower morphologies observed in these species. The results strengthen the hypothesis that a reduction in the number of interaction partners of DEF- and GLO-like proteins, with DEF-GLO heterodimers remaining the only DNA-binding dimers in core eudicots, contributed to developmental robustness, canalization of flower development and the diversification of angiosperms.