MADS life on MAdLand II: Changes in DNA-binding specificity of MADS-domain transcription factors during the transition of plants to land

我们在Madland的两个阶段的项目的首要目标是研究MIKC型MADS结构域转录因子(MTF)在植物向陆地过渡过程中的作用。MTF组成四聚体蛋白，称为花四重组样复合体(FQCs)，控制着陆地植物的主要发育过程。FQC的高结合潜力和协同DNA结合使其能够以一种特别有效和特异的方式控制靶基因的活性。FQC的这一特征可能与陆地植物复杂新奇事物的进化起源有因果联系，因此具有极大的生物学意义。MTF起源于现存的链藻的茎类群，包括所有陆地植物及其近亲(轮藻)。在Madland的第一阶段，我们证明了在现存陆地植物的茎群中，MTF的蛋白质-蛋白质相互作用结构域发生了重要的变化。这些变化是在基因复制导致MTF的两个亚家族，称为MIKCC-和MIKC*-型蛋白之后发生的。MIKCC-和MIKC*-型蛋白是两个基本独立的基因调控网络的主要组成部分，这两个网络分别控制陆地植物孢子体和配子体发育的重要方面。在Madland的第二阶段，我们想要研究地钱植物中唯一的MIKCC类型蛋白MpMADS2 FQC形成的生物学相关性，反映在植物向陆地的过渡过程中FQC形成的能力所获得的功能收益。我们将通过研究我们在第一阶段产生的无法形成FQC的MpMADS2突变体来做到这一点。此外，我们希望确定FQC的形成对所选轮藻物种的MTF全基因组DNA结合的影响。这也将为轮藻中潜在的MIKC型蛋白的目标基因提供有用的洞察，目前还没有这样的数据。此外，我们希望通过研究MTF的DNA结合MADS结构域中的主要进化变化来补充我们关于蛋白质-蛋白质相互作用结构域进化的发现。初步数据表明，在植物过渡到陆地之前存在的祖先MTF，与MIKCC-和MIKC*-型蛋白质相比，具有更混杂的DNA结合模式。在我们的项目中，我们希望确定导致DNA识别变化的MTF的MADS结构域中的突变，以及由不同类型的MTF控制的那些基因的活性的后果。

The overarching goal of our projects in both phases of MAdLand is to investigate the role of MIKC-type MADS-domain transcription factors (MTFs) during the transition of plants to land. MTFs constitute tetrameric proteins termed floral quartet-like complexes (FQCs) that control major developmental processes in land plants. The high combinatorial potential and cooperative DNA binding of FQCs enables the control of target gene activity in an especially efficient and specific way. This feature of FQCs is probably causally linked to the evolutionary origin of complex novelties in land plants and thus is of great biological interest. MTFs originated in the stem group of extant streptophytes, comprising all land plants and their closest relatives (charophyte algae). During the first phase of MAdLand we demonstrated that in the stem group of extant land plants important changes within the protein-protein interaction domain of MTFs occurred. These changes followed a gene duplication that led to two subfamilies of MTFs, termed MIKCC- and MIKC*-type proteins. MIKCC- and MIKC*-type proteins are major constituents of two largely independent gene regulatory networks that control important aspects of sporophyte and gametophyte development in land plants, respectively. In the second phase of MAdLand we want to study the biological relevance of FQC formation of the only MIKCC-type protein MpMADS2 in the liverwort M. polymorpha, reflecting the functional gain achieved by the ability of FQC formation during the transition of plants to land. We will do that by studying MpMADS2 mutants unable of FQC formation that we generated during the first phase. In addition, we want to determine the impact of FQC formation on genome-wide DNA-binding of MTFs for selected charophyte species. This will also provide useful insight into potential target genes of MIKC-type proteins in charophytes, for which no such data are available so far. Moreover, we want to complement our findings about the evolution of the protein-protein interaction domain by investigating major evolutionary changes within the DNA-binding MADS-domain of MTFs. Preliminary data suggest that ancestral MTFs that existed prior to the transition of plants to land, had a more promiscuous mode of DNA-binding than MIKCC- and MIKC*-type proteins. In our project we want to determine the mutations in the MADS-domain of MTFs that brought about these changes in DNA-recognition, and the consequences for the activity of those genes that are controlled by the different types of MTFs.