拟南芥Argonaute1/2/4/5序列分歧以及与特定miRNA的协同表达

Argonaute(Ago)是RNA诱导的基因沉默复合体（RISC）中的一个重要组成部分，在RNA沉默通路中结合小RNA发挥着关键的作用. 本文对12个物种的85个Ago/Ago-like基因序列进行了系统发育进化分析. 结果表明,植物Ago可被分为3大分支，且基因在物种产生分歧之前就已经发生了重复. 3个分支之间高同义和非同义突变频率揭示了Ago蛋白家族功能的高度保守性.采用实时荧光定量PCR对拟南芥Ago1/2/4/5在不同发育阶段和胁迫条件下的表达情况进行了分析. 结果显示,Ago1在拟南芥幼苗和成熟组织中表达显著；与23℃（最适温度）相比，16℃（亚适温度）条件下，Ago1表达量显著下调，Ago5表达量则显著上调；在脱水胁迫下，Ago5表达量下调，Ago4表达量上调. 另外，根据5′端碱基类型不同，188 954个幼苗miRNAs和2 047 843个成熟组织miRNAs被分类. 结果显示,5′端为U的miRNAs在植物中的含量最多，这与Ago1表达量最高是协同的；16℃条件下，5′ 端为C的miRNAs和Ago5表达协同上调. 这些结果都表明,Ago蛋白及其偏好的miRNAs是协同表达的.

Sequence Divergence of Arabidopsis Argonaute 1/2/4/5 and Their Coordinated Expression with Specific miRNAs

As an important component of RNA-induced silencing complexes, argonaute (Ago) proteins play a crucial role in gene silencing by associating with small RNAs. A phylogenetic tree constructed from 85 Ago/Ago-like sequences of 12 species indicated that plant Agos consisted of three branches, and Ago duplication occurred before the divergence of the current plant species. High rate of synonymous/non-synonymous substitution among the three branches indicated conserved function of the argonaute protein family. At different developmental stages or stress conditions, the expression of Ago 1/2/4/5 in Arabidopsis was examined by real-time PCR. The results showed that Ago1 was expressed at high levels in both seedlings and mature plants, but was dramatically down-regulated at 16℃ (sub-optimal temperature) as compared to those at 23℃ (optimum temperature), contrary to the expression of Ago5 which was significantly up-regulated. Under dehydration, Ago5 was down-regulated, but Ago4 was up-regulated. In plants, miRNAs with 5′ U were most abundant in both seedlings and mature plants, which is coincident with the high expression of Ago1. Under 16℃, the expression of miRNAs with 5′ C correlated with the up-regulated Ago5. These results suggested a coordinated expression of argonautes and its preferential miRNA targets.