Project description:A key step in microRNA (miRNA) biogenesis is the processing of a primary precursor RNA by the microprocessor into a precursor miRNA (pre-miRNA) intermediate. In plants, little is known about the processes that act on pre-miRNAs to influence miRNA biogenesis. Here, we performed 3’ RACE-seq to profile pre-miRNA 3’ ends in Arabidopsis. 3’ end heterogeneity was prevalent and the three microprocessor components promoted 3’ end precision. Extensive cytidylation and uridylation of precise and imprecise pre-miRNA 3’ ends were uncovered. The nucleotidyl transferase HESO1 uridylated pre-miRNAs in vitro and was responsible for most pre-miRNA uridylation in vivo. HESO1, NTP6 and NTP7 contribute to pre-miRNA cytidylation. Tailing of pre-miRNAs tended to restore trimmed pre-miRNAs to intact lengths to promote further processing. In addition, HESO1-mediated uridylation led to the degradation of some imprecisely processed pre-miRNAs. Thus, we uncovered widespread cytidylation and uridylation of pre-miRNAs and demonstrated diverse functions of pre-miRNA tailing in plants.
Project description:miRNA levels depend on both biogenesis and turnover. The methyltransferase HEN1 stabilizes plant miRNAs, animal piRNAs, and siRNAs in both kingdoms via 3' terminal methylation. Loss of HEN1 in plants results in non-templated oligo-uridylation and accelerated degradation of miRNAs. In hen1 mutants from Arabidopsis and rice, we found that the patterns of miRNA truncation and uridylation differ substantially among miRNA families, but such patterns for the same miRNA are conserved between species. miR166 and miR163 are truncated predominantly to ~17 and ~16 nt, and subsequently recover via uridylation to approximately their original sizes, 21 and 24 nt, suggesting that in these cases miRNA truncation triggers uridylation. miR171 is untruncated but uridylated to 22 nt in hen1 mutants, gaining the ability to trigger production of phased, secondary siRNAs. Truncated and tailed variants were bound by ARGONAUTE1 (AGO1) in hen1, implying that these events occur while miRNAs are still bound by AGO1. Unexpectedly, a portion of miR158 in wildtype remains unmethylated and thus subject to uridylation and destabilization, suggesting that plants naturally utilize miRNA methylation to modulate miRNA accumulation. Our results suggest that the AGO1-containing RISC complex may undergo programming to reflect each bound miRNA, determining a defined, distinct decay destiny. In this analysis, we sequenced sRNAs from two hen1 mutant alleles in Arabidopsis and three hen1 alleles in rice. In Arabidopsis, the strong hen1-1 allele in the Landsberg erecta (Ler) ecotype is the first hen1 mutant and emerged from an enhancer screen in the hua1-1/hua2-1 background, and hen1-8 in the Columbia (Col) background is a weak allele. In rice, WAVY LEAF1 (WAF1) is the ortholog of Arabidopsis HEN1, and two mutant alleles waf1-1 and waf1-2 each bear a single-base substitution leading to a premature stop codon in the second exon and a non-functional splicing site of the fourth intron, respectively. We identified a third mutant allele of the rice HEN1 gene (Oshen1-3 from the Korean (POSTEC) rice T-DNA mutant population).
Project description:miRNA levels depend on both biogenesis and turnover. The methyltransferase HEN1 stabilizes plant miRNAs, animal piRNAs, and siRNAs in both kingdoms via 3' terminal methylation. Loss of HEN1 in plants results in non-templated oligo-uridylation and accelerated degradation of miRNAs. In hen1 mutants from Arabidopsis and rice, we found that the patterns of miRNA truncation and uridylation differ substantially among miRNA families, but such patterns for the same miRNA are conserved between species. miR166 and miR163 are truncated predominantly to ~17 and ~16 nt, and subsequently recover via uridylation to approximately their original sizes, 21 and 24 nt, suggesting that in these cases miRNA truncation triggers uridylation. miR171 is untruncated but uridylated to 22 nt in hen1 mutants, gaining the ability to trigger production of phased, secondary siRNAs. Truncated and tailed variants were bound by ARGONAUTE1 (AGO1) in hen1, implying that these events occur while miRNAs are still bound by AGO1. Unexpectedly, a portion of miR158 in wildtype remains unmethylated and thus subject to uridylation and destabilization, suggesting that plants naturally utilize miRNA methylation to modulate miRNA accumulation. Our results suggest that the AGO1-containing RISC complex may undergo programming to reflect each bound miRNA, determining a defined, distinct decay destiny.
Project description:Uridylation of diverse RNA species represents an emerging theme in post-transcriptional gene regulation. In the microRNA pathway, such modifications regulate small RNA biogenesis and stability in plants, worms and mammals. Here, we report the first uridylyltransferase that acts on small RNAs in Drosophila, which we refer to as Tailor. Tailor is the source for the majority of 3´ end-modifications in microRNAs and predominantly targets precursor-hairpins. Uridylation modulates the characteristic two-nucleotide 3´ overhangs of microRNA hairpins, which regulates processing by Dicer-1 and destabilizes RNA hairpins. Furthermore, Tailor preferentially uridylates mirtron-hairpins, thereby impeding the production of non-canonical microRNAs. Mirtron-selectivity is explained by unique primary sequence specificity of Tailor, selecting RNA substrates ending with a 3´ guanosine, a feature not previously observed for TUTases. In contrast to mirtrons, conserved Drosophila pre-miRNAs are significantly depleted in 3´ guanosine, thereby escaping regulatory uridylation. Our data support the hypothesis that evolutionary adaptation to pre-miRNA uridylation shapes the nucleotide composition of pre-miRNA 3´ ends. Hence, hairpin-uridylation may serve as a barrier for the de novo creation of miRNAs in Drosophila.
Project description:Terminal uridylyl transferases (TUTs) function as integral regulators of microRNA (miRNA) biogenesis by modifying the end structure of precursor miRNA (pre-miRNA). Using biochemistry and deep sequencing techniques, we here investigate the mechanism how human TUT7 recognizes and uridylates pre-miRNAs. We show that the overhang of a pre-miRNA is the key structural element that TUT7 and its paralogues, TUT4 and TUT2, recognize. For group II pre-miRNAs which have a 1 nt 3’ overhang, TUT7 restores the canonical end structure (2 nt 3’ overhang) by mono-uridylation, and thereby promotes miRNA biogenesis. Interestingly, once the 3’ end is receded into the stem (3’ trimmed pre-miRNAs such as Ago-cleaved-pre-miRNA), TUT7 effectively generates an oligo-U tail that consequently leads to degradation. Our single-molecule study further suggests that a distributive mode is employed for both pathways, but the overhang length determines the frequency of TUT7-RNA interaction. Our results explain how TUT7 and TUT4 differentiate pre-miRNA species and reveal a role for TUT7 and TUT4 in the oligo-uridylation and removal of defective pre-miRNAs. HeLa cells were knocked down of control or TUT2/4/7, then total RNAs were prepared for RNA-seq
Project description:Terminal uridylyl transferases (TUTs) function as integral regulators of microRNA (miRNA) biogenesis by modifying the end structure of precursor miRNA (pre-miRNA). Using biochemistry and deep sequencing techniques, we here investigate the mechanism how human TUT7 recognizes and uridylates pre-miRNAs. We show that the overhang of a pre-miRNA is the key structural element that TUT7 and its paralogues, TUT4 and TUT2, recognize. For group II pre-miRNAs which have a 1 nt 3’ overhang, TUT7 restores the canonical end structure (2 nt 3’ overhang) by mono-uridylation, and thereby promotes miRNA biogenesis. Interestingly, once the 3’ end is receded into the stem (3’ trimmed pre-miRNAs such as Ago-cleaved-pre-miRNA), TUT7 effectively generates an oligo-U tail that consequently leads to degradation. Our single-molecule study further suggests that a distributive mode is employed for both pathways, but the overhang length determines the frequency of TUT7-RNA interaction. Our results explain how TUT7 and TUT4 differentiate pre-miRNA species and reveal a role for TUT7 and TUT4 in the oligo-uridylation and removal of defective pre-miRNAs.
Project description:Uridylation of diverse RNA species represents an emerging theme in post-transcriptional gene regulation. In the microRNA pathway, such modifications regulate small RNA biogenesis and stability in plants, worms and mammals. Here, we report the first uridylyltransferase that acts on small RNAs in Drosophila, which we refer to as Tailor. Tailor is the source for the majority of 3´ terminal uridine-modifications in small RNAs and predominantly targets precursor-miRNAs. Uridylation modulates the characteristic two-nucleotide 3´ overhangs of miRNA hairpins, which regulates pre-miRNA processing by Dicer-1. Furthermore, Tailor preferentially uridylates mirtron hairpins, thereby impeding the production of non-canonical microRNAs. Mirtron-selectivity is explained by unique primary sequence specificity of Tailor, selecting RNA substrates ending with a 3´ guanosine, a feature not previously observed for terminal uridylyltransferases. In contrast to mirtrons, conserved Drosophila pre-miRNAs are significantly depleted in 3´ guanosine, thereby escaping regulatory uridylation.Our data support the hypothesis that evolutionary adaptation to pre-miRNA uridylation shapes the nucleotide composition of pre-miRNA 3´ ends and may serve as a barrier for the de novo creation of miRNAs in Drosophila.
Project description:Recent small RNA sequencing data has uncovered extensive modification of the 3’ end of mature microRNAs (miRNAs). This non-templated nucleotide addition can impact miRNA gene regulatory networks through the control of miRNA stability or by interfering with the repression of target mRNAs. The miRNA modifying enzymes responsible for this regulation remain largely uncharacterized. Here we describe the ability for two related terminal uridyl transferases (TUTases), Zcchc6 (TUT7) and Zcchc11 (TUT4), to 3’ mono-uridylate a specific subset of miRNAs involved in cell differentiation and Hox gene control. Zcchc6/11 selectively uridylate these miRNAs in vitro, and we biochemically define a bipartite sequence motif that is necessary and sufficient to confer Zcchc6/11 catalyzed uridylation. Depletion of these TUTases in cultured cells causes the selective loss of 3’ mono-uridylation of many of the same miRNAs. Interestingly, upon TUTase dependent loss of uridylation we observe a concomitant increase in non-templated 3’ mono-adenylation. Our results uncover the molecular basis for sequence specific miRNA mono-uridylation by Zcchc6/11, highlight the precise control of different 3’ miRNA modifications in cells, and have implications for miRNA regulation during development. small RNA profiles in TUTases knock-down and control HeLa cells were generated by Illumina deep sequencing
Project description:Phased, secondary siRNAs (phasiRNAs) represent a class of small RNAs in plants generated via distinct biogenesis pathways, predominantly dependent on the activity of 22 nt miRNAs. Most 22 nt miRNAs are processed by DCL1 from miRNA precursors containing an asymmetric bulge, yielding a 22/21 nt miRNA/miRNA* duplex. Here we show that miR1510, a soybean miRNA capable of triggering phasiRNA production from numerous NB-LRRs, previously described as 21 nt in its mature form, primarily accumulates as a 22 nt isoform via monouridylation. We demonstrate that in Arabidopsis, this uridylation is performed by HESO1. Biochemical experiments showed that the 3' terminus of miR1510 is only partially 2'-O-methylated, because of the terminal mispairing in the miR1510/miR1510* duplex that inhibits HEN1 activity in soybean. miR1510 emerged in the Phaseoleae ~41 to 42 MYA with a conserved precursor structure yielding a 22 nt monouridylated form, yet a variant in mung bean is processed directly in a 22 nt mature form. This analysis of miR1510 yields two observations: (1) plants can utilize post-processing modification to generate abundant 22 nt miRNA isoforms to more efficiently regulate target mRNA abundances; (2) comparative analysis demonstrates an example of selective optimization of precursor processing of a young plant miRNA.
Project description:Using 3' RACE-seq method, we analyzed the impact of URT1 and/or HESO1 inactivation on the uridylation of GFLV, TuMV and TCV RNAs in Arabidopsis.