Department of Molecular Plant Genetics, Max Planck Institute for Plant Breeding Research, Cologne, Germany.
Mol Biol Evol. 2010 May;27(5):1201-11. doi: 10.1093/molbev/msq005. Epub 2010 Jan 15.
Land plants (embryophytes) are characterized by an alternation of two generations, the haploid gametophyte and the diploid sporophyte. The development of the small and simple male gametophyte of the flowering plant Arabidopsis (Arabidopsis thaliana) critically depends on the action of five MIKC* group MCM1-AGAMOUS-DEFICIENS-SRF-box (MADS-box) proteins. In this study, these MIKC* MADS-box genes were isolated from land plants with relatively large and complex gametophyte bodies, namely the bryophytes. We found that although the gene family expanded in the mosses Sphagnum subsecundum, Physcomitrella patens, and Funaria hygrometrica, only a single homologue, Marchantia polymorpha MADS-box gene 1 (MpMADS1), has been retained in the liverwort M. polymorpha. Liverworts are the earliest diverging land plants, and so a comparison of MpMADS1 with its angiosperm homologues addresses the molecular evolution of an embryophyte-specific transcription factor over the widest phylogenetic distance. MpMADS1 was found to form a homodimeric DNA-binding complex, which is in contrast to the Arabidopsis proteins that are functional only as heterodimeric complexes. The M. polymorpha homodimer, nevertheless, recognizes the same DNA sequences as its angiosperm counterparts and can functionally replace endogenous MIKC* complexes to a significant extent when heterologously expressed in Arabidopsis pollen. The 11 MIKC* homologues from the moss F. hygrometrica are highly and almost exclusively expressed in the gametophytic generation. Taken together, these findings suggest that MIKC* MADS-box proteins have largely preserved molecular roles in the gametophytic generation of land plants.
陆生植物（胚胎植物）的特征是具有两个世代的交替，即单倍体配子体和二倍体孢子体。拟南芥（Arabidopsis thaliana）的小而简单的雄性配子体的发育严重依赖于五个 MIKC组 MCM1-AGAMOUS-DEFICIENS-SRF-box（MADS-box）蛋白的作用。在这项研究中，从具有相对较大和复杂配子体的陆生植物中分离出这些 MIKCMADS-box 基因，即苔藓植物。我们发现，尽管基因家族在藓类植物 Sphagnum subsecundum、Physcomitrella patens 和 Funaria hygrometrica 中扩张，但只有一个同源物，即 Marchantia polymorpha MADS-box 基因 1（MpMADS1），在苔类植物 M. polymorpha 中被保留下来。苔类植物是最早分化的陆地植物，因此将 MpMADS1 与其被子植物同源物进行比较，可以解决胚胎植物特有的转录因子在最广泛的系统发育距离上的分子进化问题。发现 MpMADS1 形成同源二聚体 DNA 结合复合物，与拟南芥蛋白形成功能性异源二聚体复合物形成对比。然而，M. polymorpha 同源二聚体识别与同源物相同的 DNA 序列，并且当在拟南芥花粉中异源表达时可以在很大程度上替代内源性 MIKC复合物发挥功能。藓类植物 F. hygrometrica 的 11 个 MIKC同源物在配子体世代中高度且几乎完全表达。总之，这些发现表明 MIKC*MADS-box 蛋白在陆地植物的配子体世代中基本上保留了分子作用。
