Fast and Efficient 5'P Degradome Library Preparation for Analysis of Co-Translational Decay in Arabidopsis

Molecular Insights into MpAGO1 and Its Regulatory miRNA, miR11707, in the High-Temperature Acclimation of Marchantia polymorpha

As a model plant for bryophytes, Marchantia polymorpha offers insights into the role of RNA silencing in aiding early land plants navigate the challenges posed by high-temperature environments. Genomic analysis revealed unique ARGONAUTE1 ortholog gene (MpAGO1) in M. polymorpha, which is regulated by two species-specific microRNAs (miRNAs), miR11707.1 and miR11707.2. Comparative studies of small RNA profiles from M. polymorpha cellular and MpAGO1 immunoprecipitation (MpAGO1-IP) profiles at various temperatures, along with analyses of Arabidopsis AGO1 (AtAGO1), revealed that MpAGO1 has a low selectivity for a diverse range of small RNA species than AtAGO1. Protein structural comparisons revealed no discernible differences in the guide strand small RNA recognition middle domain, MID domain, of MpAGO1 and AtAGO1, suggesting the complexity of miRNA species specificity and necessitating further exploration. Small RNA profiling and size exclusion chromatography have pinpointed a subset of M. polymorpha miRNAs, notably miR11707, that remain in free form within the cell at 22°C but are loaded into MpAGO1 at 28°C to engage in RNA silencing. Investigations into the mir11707 gene editing (mir11707ge) mutants provided evidence of the regulation of miR11707 in MpAGO1. Notably, while MpAGO1 mRNA expression decreases at 28°C, the stability of the MpAGO1 protein and its associated miRNAs is essential for enhancing the RNA-inducing silencing complex (RISC) activity, revealing the importance of RNA silencing in enabling M. polymorpha to survive thermal stress. This study advances our understanding of RNA silencing in bryophytes and provides groundbreaking insights into the evolutionary resilience of land plants to climatic adversities.

Multi-transcriptomics identifies targets of the endoribonuclease DNE1 and highlights its coordination with decapping

Decapping is a crucial step in mRNA degradation in eucaryotes and requires the formation of a holoenzyme complex between the decapping enzyme DECAPPING 2 (DCP2) and the decapping enhancer DCP1. In Arabidopsis (Arabidopsis thaliana), DCP1-ASSOCIATED NYN ENDORIBONUCLEASE 1 (DNE1) is a direct protein partner of DCP1. The function of both DNE1 and decapping is necessary to maintain phyllotaxis, the regularity of organ emergence in the apex. In this study, we combined in vivo mRNA editing, RNA degradome sequencing, transcriptomics, and small RNA-omics to identify targets of DNE1 and study how DNE1 and DCP2 cooperate in controlling mRNA fate. Our data reveal that DNE1 mainly contacts and cleaves mRNAs in the coding sequence and has sequence cleavage preferences. DNE1 targets are also degraded through decapping, and both RNA degradation pathways influence the production of mRNA-derived small interfering RNAs. Finally, we detected mRNA features enriched in DNE1 targets including RNA G-quadruplexes and translated upstream open reading frames. Combining these four complementary high-throughput sequencing strategies greatly expands the range of DNE1 targets and allowed us to build a conceptual framework describing the influence of DNE1 and decapping on mRNA fate. These data will be crucial to unveil the specificity of DNE1 action and understand its importance for developmental patterning.

Genome-wide analysis of mRNA decay in Arabidopsis shoot and root reveals the importance of co-translational mRNA decay in the general mRNA turnover

Until recently, the general 5'-3' mRNA decay was placed in the cytosol after the mRNA was released from ribosomes. However, the discovery of an additional 5' to 3' pathway, the Co-Translational mRNA Decay (CTRD), changed this paradigm. Up to date, defining the real contribution of CTRD in the general mRNA turnover has been hardly possible as the enzyme involved in this pathway is also involved in cytosolic decay. Here we overcame this obstacle and created an Arabidopsis line specifically impaired for CTRD called XRN4ΔCTRD. Through a genome-wide analysis of mRNA decay rate in shoot and root, we tested the importance of CTRD in mRNA turnover. First, we observed that mRNAs tend to be more stable in root than in shoot. Next, using XRN4ΔCTRD line, we demonstrated that CTRD is a major determinant in mRNA turnover. In shoot, the absence of CTRD leads to the stabilization of thousands of transcripts while in root its absence is highly compensated resulting in faster decay rates. We demonstrated that this faster decay rate is partially due to the XRN4-dependent cytosolic decay. Finally, we correlated this organ-specific effect with XRN4ΔCTRD line phenotypes revealing a crucial role of CTRD in mRNA homeostasis and proper organ development.

Diurnal gene oscillations modulated by RNA metabolism in tomato

Diurnal rhythms are known to regulate the expression of a large number of genes, coordinating plant growth and development with diel changes in light and temperature. However, the impact of RNA metabolism on rhythmic gene oscillations in plant is not yet fully understood. To address this question, we performed transcriptome and degradome profiling on tomato leaves at 6 time points during one 24 h cycle, using RNA-seq and genome-wide mapping of uncapped and cleavage transcripts (GMUCT). Time-series profiling of RNA-seq revealed 9342 diurnal-oscillated genes, which were enriched in various metabolic processes. To quantify the general level of RNA degradation for each gene, we utilized the Proportion Uncapped (PU) metric, which represents the GMUCT/RNA-seq ratio. Oscillated PU analysis revealed that 3885 genes were regulated by rhythmic RNA degradation. The RNA decay of these diurnal genes was highly coordinated with mRNA downregulation during oscillation, highlighting the critical role of internal transcription-degradation balance in rhythmic gene oscillation. Furthermore, we identified 2190 genes undergoing co-translational RNA decay (CTRD) with 5' phosphate read ends enriched at the boundary of ribosomes stalling at translational termination sites. Interestingly, diurnal-changed mRNAs with large amplitudes tended to be co-translationally decay, suggesting that CTRD contributed to the rapid turnover of diurnal mRNAs. Finally, we also identified several genes, whose miRNA cleavage efficiency oscillated in a diurnal manner. Taken together, these findings uncovered the vital functions of RNA metabolism, including rhythmic RNA degradation, CTRD, and miRNA cleavage, in modulating the diurnal mRNA oscillations during diel change at post-transcriptional level in tomato.

RNA degradome analysis reveals DNE1 endoribonuclease is required for the turnover of diverse mRNA substrates in Arabidopsis

In plants, cytoplasmic mRNA decay is critical for posttranscriptionally controlling gene expression and for maintaining cellular RNA homeostasis. Arabidopsis DCP1-ASSOCIATED NYN ENDORIBONUCLEASE 1 (DNE1) is a cytoplasmic mRNA decay factor that interacts with proteins involved in mRNA decapping and nonsense-mediated mRNA decay (NMD). There is limited information on the functional role of DNE1 in RNA turnover, and the identities of its endogenous targets are unknown. In this study, we utilized RNA degradome approaches to globally investigate DNE1 substrates. Monophosphorylated 5' ends, produced by DNE1, should accumulate in mutants lacking the cytoplasmic exoribonuclease XRN4, but be absent from DNE1 and XRN4 double mutants. In seedlings, we identified over 200 such transcripts, most of which reflect cleavage within coding regions. While most DNE1 targets were NMD-insensitive, some were upstream ORF (uORF)-containing and NMD-sensitive transcripts, indicating that this endoribonuclease is required for turnover of a diverse set of mRNAs. Transgenic plants expressing DNE1 cDNA with an active-site mutation in the endoribonuclease domain abolished the in planta cleavage of transcripts, demonstrating that DNE1 endoribonuclease activity is required for cleavage. Our work provides key insights into the identity of DNE1 substrates and enhances our understanding of DNE1-mediated mRNA decay.

Identification of short open reading frames in plant genomes

The roles of short/small open reading frames (sORFs) have been increasingly recognized in recent years due to the rapidly growing number of sORFs identified in various organisms due to the development and application of the Ribo-Seq technique, which sequences the ribosome-protected footprints (RPFs) of the translating mRNAs. However, special attention should be paid to RPFs used to identify sORFs in plants due to their small size (~30 nt) and the high complexity and repetitiveness of the plant genome, particularly for polyploidy species. In this work, we compare different approaches to the identification of plant sORFs, discuss the advantages and disadvantages of each method, and provide a guide for choosing different methods in plant sORF studies.

Degradome Assisted Plant MicroRNA Prediction Under Alternative Annotation Criteria

Current microRNA (miRNA) prediction methods are generally based on annotation criteria that tend to miss potential functional miRNAs. Recently, new miRNA annotation criteria have been proposed that could lead to improvements in miRNA prediction methods in plants. Here, we investigate the effect of the new criteria on miRNA prediction in Arabidopsis thaliana and present a new degradome assisted functional miRNA prediction approach. We investigated the effect by applying the new criteria, and a more permissive criteria on miRNA prediction using existing miRNA prediction tools. We also developed an approach to miRNA prediction that is assisted by the functional information extracted from the analysis of degradome sequencing. We demonstrate the improved performance of degradome assisted miRNA prediction compared to unassisted prediction and evaluate the approach using miRNA differential expression analysis. We observe how the miRNA predictions fit under the different criteria and show a potential novel miRNA that has been missed within Arabidopsis thaliana. Additionally, we introduce a freely available software 'PAREfirst' that employs the degradome assisted approach. The study shows that some miRNAs could be missed due to the stringency of the former annotation criteria, and combining a degradome assisted approach with more permissive miRNA criteria can expand confident miRNA predictions.