MAC3 Proteins Regulate MicroRNA Biogenesis

Li et al. uncovered the roles of MAC3 in miRNA biogenesis in Arabidopsis. Plant Cell (2018).

By Shengjun Li and Bin Yu

Background: microRNAs (miRNAs) are tiny RNA molecules that regulate gene expression. Plants use miRNAs to control development and physiology. Consequently, understanding of the mechanism governing miRNA production is fundamental to plant biology and is essential for improving crop traits. miRNAs are generated from precursor molecules called primary miRNA transcripts (pri-miRNAs) that are majorly transcribed by DNA-dependent RNA polymerase II (Pol II). In plants, pri-miRNAs are cut by a protein complex containing the RNase III enzyme DICER-LIKE1 (DCL1), the RNA-binding protein HYL1 and the zinc-finger protein SERRATE (SE) to release miRNAs. However, it is not well defined how the transcription and processing of pri-miRNAs are regulated to control miRNA production.

Question: MAC3A and MAC3B, two ortholog proteins, are key components of the MOS4-associated complex that is required for plant development and immunity to bacterial infection. We wanted to know the role of MAC3A and MAC3B in miRNA production. We examined how MAC3A and MAC3B modulate the activity of the DCL1 complex.

Finding: We found that MAC3A and MAC3B positively regulate miRNA accumulation through promoting pri-miRNA stability and the activity of the DCL1 complex. They interact with the DCL1 complex and are required for the DCL1 complex formation. Moreover, we showed that MAC3A is a phosphorylation-depended E3 ubiquitin ligase and this enzymatic activity is essential for miRNA production. These results reveal that certain signals can modulate MAC3A activity through phosphorylation, and thereby regulate miRNA accumulation.

Next steps: We are working on how MAC3A and MAC3B act coordinately with other MAC components to control miRNA biogenesis. Moreover, we are studying the biological significance of phosphorylation-dependent E3 ubiquitin ligase activity of MAC3A in miRNA biogenesis by identifying the enzyme that phosphorylates MAC3A and the substrates of MAC3A.

Li, S., Liu K, Zhou, B., Li, M., Zhang, M., Zeng, L., Zhang, C. and Yu, B. (2018). MAC3A and MAC3B, two core subunits of the MOS4-associated complex, positively impact miRNA biogenesis. Plant Cell 30: 481-494; DOI:

Key words: Development, Gene Regulation, miRNA Biogenesis, Molecular biology