miR156靶基因SPL在植物中的系统分布和进化模式分析

Squamosa promoter binding protein like genes (SPLs)在植物发育过程中具有重要作用。很多SPLs被miR156调节，然而，对于它们在植物中的系统分布和进化模式还知之甚少。本文对9个测序物种（藻类，苔藓，石松，单子叶和双子叶植物）的183个SPLs进行了生物信息学分析。结果表明miR156应答元件（MREs）仅在陆生植物SPLs中发现，藻类中不存在。系统进化分析显示陆生植物SPLs分为两大分支：group I和group II。 MiR156靶基因仅分布于group II，表明它们有着共同的祖先。Group II进一步分为7个亚支(IIa IIg)，miR156靶基因分布在除IId外的其余6个亚支的特定SPLs。系统分类与基因结构的相关性反映了SPL靶基因结构上的变化。在进化过程中，它们可能发生外显子的丢失且伴随MRE的丢失。另外，基因重复对SPL靶基因的丰度变化影响很大，尤其是被子植物与低等植物分歧后它们数量明显增加。以拟南芥为模式植物分析发现串联重复和片段重复是SPL靶基因扩张的主要机制。

Unraveling the Distribution and Evolution of miR156-targeted SPLs in Plants by Phylogenetic Analysis

Squamosa promoter-binding protein-like genes (SPLs) are critical during plant development and mostly regulated by miR156. However, little is known about phylogenetic distribution and evolutionary patterns of miR156-targeted SPLs. In this study, 183 SPLs from nine genome-sequenced species representing algae, bryophytes, lycophyte, monocots, and eudicots were computationally analyzed. Our results showed that miR156 responsive elements (MREs) on SPLs were present in land plants but absent from unicellular green algae. Phylogenetic analysis revealed that miR156-targeted SPLs only distributed in group II not group I of land plants, suggesting they originated from a common ancestor. In addition, group II were further divided into seven subgroups (IIa-IIg) and miR156-targeted SPLs distributed in some specific members of SPLs from six subgroups except subgroup IId. Such distribution pattern was well elucidated by gene structure evolution of miR156-targeted SPLs based on the correlation of phylogenetic classification and gene structure. They could suffer from the exon loss events combined with MREs loss during evolution. Moreover, gene duplication contributed to the abundance of miR156-targeted SPLs, which had significantly increased after angiosperms and lower plants split. With Arabidopsis as the model species, we found segmental and tandem gene duplications predominated during miR156-targeted SPLs expansion. Taken together, these results provide better insights in understanding the function diversity and evolution of miR156-targeted SPLs in plants.