On Nov. 21, 2016, Prof. Yijun Qi’s group published a research paper in the recent issue of The Plant Cell entitled “Transportin1 promotes the association of microRNA with Argonaute1 in Arabidopsis”. The paper reported an important role of Transportin1 in regulating miRNA activity in Arabidopsis.
In Arabidopsis, microRNAs (miRNAs) are mainly loaded into Argonaute 1 (AGO1) to post-transcriptionally regulate gene expression. Prof. Qi’s group has previously found that Enhanced MiRNA Activity 1 (EMA1), an importin β family protein, negatively regulates miRNA loading into AGO1. In this paper, they performed a suppressor screening of ema1 and identified another importin β protein, Transportin 1 (TRN1), as a new regulatory component in the miRNA pathway. Mutation of TRN1 did not reduce miRNA accumulation but impaired miRNA activity. They found that TRN1 interacted with AGO1. Mutation of the three conserved residues required for cargo recognition of TRN1 reduced its interaction with AGO1 and compromised its function in regulating miRNA activity. Intriguingly, TRN1 dysfunction did not change the cytoplasmic-nuclear distribution of miRNAs and AGO1 but reduced the amount of miRNAs associated with AGO1. These results indicate that TRN1 positively regulates miRNA activity by promoting the association of miRNAs with AGO1 and reveal opposing roles of two importin β family proteins in miRNA loading.
Ph.D student Yuwei Cui and post-doc Xiaofeng Fang from School of Life Sciences at Tsinghua University are the co-first authors of the paper. The study was supported by grants from Ministry of Science and Technology of China, Tsinghua-Peking Joint Center for Life Sciences, and National Science Foundation of China.
Figure 1. Transportin1 and Importin β together balance the association of microRNAs with Argonaute1 in Arabidopsis