Shan Hongyan, Zhang Ning, Liu Cuijing, Xu Guixia, Zhang Jian, Chen Zhiduan, Kong Hongzhi
State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, The Chinese Academy of Sciences, Xiangshan, Beijing, People's Republic of China.
Mol Phylogenet Evol. 2007 Jul;44(1):26-41. doi: 10.1016/j.ympev.2007.02.016. Epub 2007 Feb 25.
Members of the AP1/SQUA subfamily of plant MADS-box genes play broad roles in the regulation of reproductive meristems, the specification of sepal and petal identities, and the development of leaves and fruits. It has been shown that AP1/SQUA-like genes are angiosperm-specific, and have experienced several major duplication events. However, the evolutionary history of this subfamily is still uncertain. Here, we report the isolation of 14 new AP1/SQUA-like genes from seven early-diverging eudicots and the identification of 11 previously uncharacterized ESTs and genomic sequences from public databases. Sequence comparisons of these and other published sequences reveal a conserved C-terminal region, the FUL motif, in addition to the known euAP1/paleoAP1 motif, in AP1/SQUA-like proteins. Phylogenetic analyses further suggest that there are three major lineages (euAP1, euFUL, and AGL79) in core eudicots, likely resulting from two close duplication events that predated the divergence of core eudicots. Among the three lineages, euFUL is structurally very similar to FUL-like genes from early-diverging eudicots and basal angiosperms, whereas euAP1 might have originally been generated through a 1-bp deletion in the exon 8 of an ancestral euFUL- or FUL-like gene. Because euFUL- and FUL-like genes usually have broad expression patterns, we speculate that AP1/SQUA-like genes initially had broad functions. Based on these observations, the evolutionary fates of duplicate genes and the contributions of the frameshift mutation and alternative splicing to functional diversity are discussed.
植物MADS-box基因的AP1/SQUA亚家族成员在生殖分生组织的调控、萼片和花瓣特征的确定以及叶片和果实的发育过程中发挥着广泛作用。研究表明，AP1/SQUA类基因是被子植物特有的，并且经历了几次主要的复制事件。然而，该亚家族的进化历史仍不明确。在此，我们报告了从七种早期分化的真双子叶植物中分离出14个新的AP1/SQUA类基因，并从公共数据库中鉴定出11个先前未表征的EST和基因组序列。对这些序列以及其他已发表序列的比较揭示，除了已知的euAP1/paleoAP1基序外，AP1/SQUA类蛋白中还有一个保守的C端区域，即FUL基序。系统发育分析进一步表明，在核心真双子叶植物中有三个主要谱系（euAP1、euFUL和AGL79），这可能是由核心真双子叶植物分化之前的两次紧密复制事件导致的。在这三个谱系中，euFUL在结构上与早期分化的真双子叶植物和基部被子植物中的FUL类基因非常相似，而euAP1可能最初是通过祖先euFUL或FUL类基因外显子8中的1个碱基缺失产生的。由于euFUL和FUL类基因通常具有广泛的表达模式，我们推测AP1/SQUA类基因最初具有广泛的功能。基于这些观察结果，我们讨论了重复基因的进化命运以及移码突变和可变剪接对功能多样性的贡献。
