miRNAs play critical roles in almost every biological processes in eukaryotes. The tiny RNAs function in cytoplasm to silence target transcripts whereas they are born in nucleus in plants. On the other hand, the factory components that are used to produce miRNAs are made in cytoplasm while they need to be transported into the nucleus to process raw miRNA precursors. HYL1 is one of the core components in the factory in the model plant Arabidopsis. Here, the Zhang lab fellows applied a proteomics approach and identified an importin β-protein, KETCH1, as a partner of HYL1 protein. KETCH1 mutation causes developmental defect, reminiscent of mutants in the miRNA pathway. The mutation also reduces miRNA abundance but does not affect its nuclear-cytoplasmic distribution. Rather, KETCH1 mutation decreases the accumulation of HYL1 protein in the nucleus and compromises the HYL1-mediated miRNA production. Thus, they concluded that KETCH1 specifically transports HYL1 into the nucleus to facilitate miRNA production. Given that HYL1 and importin β-proteins are all conserved in various organisms, this study sheds light on the poorly understood nuclear-cytoplasmic trafficking of miRNA-producing machinery through eukaryotes.
The co-1st authors are Dr. Zhonghui Zhang, and former graduate Ms. Chunxiao Ge from the Zhang lab and Ms. Xinwei Guo, a visiting student from the laboratory of Dr. Tianhong Li at China Agricultural University. The study also involved the collaboration from the laboratories of Drs. Hisashi Koiwa at Department of Horticulture, TAMU and Seong Wook Yang, Yonsei University, Republic of Korea. The picture shows the function model of KETCH1 protein in vivo. For further reading, please see
- Zhang Z, Guo X, Ge C, Ma Z, Jiang M, Li T, Koiwa H, Yang SW, Zhang X. (2017) KETCH1 imports HYL1 to nucleus for miRNA biogenesis in Arabidopsis. Proc Natl Acad Sci USA. pii: 201619755. doi: 10.1073/pnas.1619755114.
- Zhang Z, Hu F, Sung MW, Shu C, Castillo-González C, Koiwa H, Tang G, Dickman M, Li P, Zhang X, RISC-interacting clearing 3′- 5′ exoribonucleases (RICEs) degrade uridylated cleavage fragments to maintain functional RISC in Arabidopsis thaliana. eLife May 2;6. pii: e24466. doi: 10.7554/eLife.24466
- AgriLife Today