microRNA biogenesis, degradation and activity in plants

Abstract

microRNAs (miRNAs) are important regulators of gene expression. After excised from primary miRNA transcript by dicer-like1 (DCL1, an RNAse III enzyme), miRNAs bind and guide their effector protein named argonaute 1 (AGO1) to silence the expression of target RNAs containing their complementary sequences in plants. miRNA levels and activities are tightly controlled to ensure their functions in various biological processes such as development, metabolism and responses to abiotic and biotic stresses. Studies have identified many factors that involve in miRNA accumulation and activities. Characterization of these factors in turn greatly improves our understanding of the processes related to miRNAs. Here, we review recent progress of mechanisms underlying miRNA expression and functions in plants.

DELAY OF GERMINATION1 ( DOG1 ) regulates both seed dormancy and flowering time through microRNA pathways

“…4 E-G), and previous studies found that miR156 and miR172 levels are altered in mutants of DCL1, HYL1, SE, TGH, and CDC5 (42,56,58,62,63). However, multiple feedback loops are associated with transcription and processing of miRNAs (41), so further study is needed to clarify the specific mechanism by which DOG1 affects miRNA levels. In addition, the strong effects of DOG1 overexpression in enhancing seed dormancy even in the absence of MIR156 overexpression (SI Appendix, Fig.…”

“…miRNAs have been implicated previously as being involved separately in seed germination and flowering time (30,32). Mutants that are defective in DCL1, HYL1, and SE, all of which are required for miRNA biogenesis (41), display abnormal flowering and alteration in ABA sensitivity of seed germination (54,55). Interestingly, the delayed-flowering phenotype of dcl1-7 mutant could be rescued by expression of a DCL4-dependent MIR839 in which the mature sequence was replaced by the one encoding MIR172, suggesting that the delayed flowering in dcl1-7 plants is a result of the reduction in miR172 (56).…”

“…4 A and B), we tested whether transcripts of genes encoding proteins associated with miRNA transcription or processing were altered. After preliminary screening, we focused on five genes: DICER-LIKE 1 (DCL1), HYPONASTIC LEAVES1 (HYL1), the G-patch domain protein TOUGH (TGH), the zinc finger protein SERRATE (SE), and CELL DIVISION CYCLE 5 (CDC5) that binds RNA polymerase II and MIR promoters to positively regulate transcription of MIR-encoding genes (41,42). Although the specific effects varied somewhat among the Arabidopsis and lettuce genotypes and mutants tested, transcript levels of all of these genes differed from their respective WTs in at least some cases (Fig.…”

RNA-binding protein DUS16 plays an essential role in primary miRNA processing in the unicellular alga Chlamydomonas reinhardtii

“…Although many RNA-binding proteins have been well characterized as essential factors for the production of miRNAs in animals and plants, the composition of RNA-binding domains in DUS16 is unique among them (6)(7)(8)49). Dead End 1 (Dnd1) does consist of a single RRM and a single dsRBD, but it counteracts the function of miRNAs by binding to transcripts at miRNA target sites in humans and zebrafish and is not involved in miRNA biogenesis (58).…”

“…Several RNA-binding proteins play important roles in producing subsets of miRNAs by assisting the accurate and efficient processing of pri-miRNA and pre-miRNAs in animals and plants (6)(7)(8). In humans, pri-miRNAs are cotranscriptionally recognized by the microprocessor complex consisting of the RNase III enzyme Drosha and the dsRNA-binding protein DGCR8 and then are processed to liberate pre-miRNA hairpins from pri-miRNA in the nucleus (9)(10)(11)(12).…”