Stiller John W, Yang Chunlin, Collén Jonas, Kowalczyk Nathalie, Thompson Beth E
Department of Biology, East Carolina University, Greenville, North Carolina, 27858, USA.
Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana, 46202, USA.
J Phycol. 2018 Dec;54(6):879-887. doi: 10.1111/jpy.12795. Epub 2018 Oct 25.
Red algae are the oldest identifiable multicellular eukaryotes, with a fossil record dating back more than a billion years. During that time two major rhodophyte lineages, bangiophytes and florideophytes, have evolved varied levels of morphological complexity. These two groups are distinguished, in part, by different patterns of multicellular development, with florideophytes exhibiting a far greater diversity of morphologies. Interestingly, during their long evolutionary history, there is no record of a rhodophyte achieving the kinds of cellular and tissue-specific differentiation present in other multicellular algal lineages. To date, the genetic underpinnings of unique aspects of red algal development are largely unexplored; however, they must reflect the complements and patterns of expression of key regulatory genes. Here we report comparative evolutionary and gene expression analyses of core subunits of the SWI/SNF chromatin-remodeling complex, which is implicated in cell differentiation and developmental regulation in more well studied multicellular groups. Our results suggest that a single, canonical SWI/SNF complex was present in the rhodophyte ancestor, with gene duplications and evolutionary diversification of SWI/SNF subunits accompanying the evolution of multicellularity in the common ancestor of bangiophytes and florideophytes. Differences in how SWI/SNF chromatin remodeling evolved subsequently, in particular gene losses and more rapid divergence of SWI3 and SNF5 in bangiophytes, could help to explain why they exhibit a more limited range of morphological complexity than their florideophyte cousins.
红藻是最古老的可识别多细胞真核生物，其化石记录可追溯到十亿多年前。在那段时间里，红藻的两个主要谱系，即红毛菜纲和真红藻纲，进化出了不同程度的形态复杂性。这两个类群部分是通过不同的多细胞发育模式来区分的，真红藻纲表现出更为多样的形态。有趣的是，在它们漫长的进化历史中，没有记录表明红藻能够实现其他多细胞藻类谱系中存在的那种细胞和组织特异性分化。迄今为止，红藻发育独特方面的遗传基础在很大程度上尚未被探索；然而，它们必定反映了关键调控基因的互补和表达模式。在这里，我们报告了SWI/SNF染色质重塑复合体核心亚基的比较进化和基因表达分析，该复合体在研究更深入的多细胞类群中与细胞分化和发育调控有关。我们的结果表明，红藻祖先中存在一个单一的、典型的SWI/SNF复合体，随着红毛菜纲和真红藻纲共同祖先中多细胞性的进化，SWI/SNF亚基发生了基因复制和进化多样化。随后SWI/SNF染色质重塑的进化差异，特别是红毛菜纲中SWI3和SNF5的基因丢失和更快的分化，可能有助于解释为什么它们的形态复杂性范围比其真红藻纲的近亲更为有限。
