Mol Plant. 2021 April 05; 14(4): 541–543. doi:10.1016/j.molp.2021.02.009
MicroRNAs (miRNAs) are one of the most important regulators of gene expression. Their biogenesis starts with the transcription of primary miRNA transcripts (pri-miRNAs). In plants, the RNase III enzyme DICER-LIKER 1 (DCL1), together with its partner, the double-stranded RNA-binding protein HYPONASTIC LEAVES 1 (HYL1), and the zinc-finger protein SERRATE (SE), process the imperfect miRNA-residing stem loop of primiRNAs to release the miRNA/miRNA* duplexes in the nucleus, which are then methylated by HUA1 ENHANCER 1 (Rogers and Chen, 2013; Song et al., 2019). Then, most miRNAs are sorted into AGONAUTE 1 to mediate mRNA-cleavage or translation inhibition based on sequence complementarity (Rogers and Chen, 2013; Song et al., 2019). Studies have shown that miRNA biogenesis is controlled through modulating pri-miRNA transcription, stability and processing, which is often coupled with various developmental and environmental signals. In a recent study, Park et al. (2021) found that forkhead-associated domain 2 (FHA2) negatively regulates miRNA biogenesis. It interacts with DCL1 to repress pri-miRNA processing. Remarkably, FHA2 is stabilized by light and modulates light-triggered changes in pri-miRNA processing during de-etiolation, suggesting that FHA2 links light signal to miRNA biogenesis (Park et al., 2021).