Posttranscriptional coordination of splicing and miRNA biogenesis in plants

MiRNAs differentially expressed in vegetative and reproductive organs of Marchantia polymorpha - insights into their expression pattern, gene structures and function

MicroRNAs regulate gene expression affecting a variety of plant developmental processes. The evolutionary position of Marchantia polymorpha makes it a significant model to understand miRNA-mediated gene regulatory pathways in plants. Previous studies focused on conserved miRNA-target mRNA modules showed their critical role in Marchantia development. Here, we demonstrate that the differential expression of conserved miRNAs among land plants and their targets in selected organs of Marchantia additionally underlines their role in regulating fundamental developmental processes. The main aim of this study was to characterize selected liverwort-specific miRNAs, as there is a limited knowledge on their biogenesis, accumulation, targets, and function in Marchantia. We demonstrate their differential accumulation in vegetative and generative organs. We reveal that all liverwort-specific miRNAs examined are encoded by independent transcriptional units. MpmiR11737a, MpmiR11887 and MpmiR11796, annotated as being encoded within protein-encoding genes, have their own independent transcription start sites. The analysis of selected liverwort-specific miRNAs and their pri-miRNAs often reveal correlation in their levels, suggesting transcriptional regulation. However, MpmiR11796 shows a reverse correlation to its pri-miRNA level, suggesting post-transcriptional regulation. Moreover, we identify novel targets for selected liverwort-specific miRNAs and demonstrate an inverse correlation between their expression and miRNA accumulation. In the case of one miRNA precursor, we provide evidence that it encodes two functional miRNAs with two independent targets. Overall, our research sheds light on liverwort-specific miRNA gene structure, provides new data on their biogenesis and expression regulation. Furthermore, identifying their targets, we hypothesize the potential role of these miRNAs in early land plant development and functioning.

Intronic microRNA-directed regulation of mitochondrial reactive oxygen species enhances plant stress tolerance in Arabidopsis

MicroRNAs (miRNAs) play crucial roles in regulating plant development and stress responses. However, the functions and mechanism of intronic miRNAs in plants are poorly understood. This study reports a stress-responsive RNA splicing mechanism for intronic miR400 production, whereby miR400 modulates reactive oxygen species (ROS) accumulation and improves plant tolerance by downregulating its target expression. To monitor the intron splicing events, we used an intronic miR400 splicing-dependent luciferase transgenic line. Luciferase activity was observed to decrease after high cadmium concentration treatment due to the retention of the miR400-containing intron, which inhibited the production of mature miR400. Furthermore, we demonstrated that under Cd treatments, Pentatricopeptide Repeat Protein 1 (PPR1), the target of miR400, acts as a positive regulator by inducing ROS accumulation. Ppr1 mutation affected the Complex III activity in the electron transport chain and RNA editing of the mitochondrial gene ccmB. This study illustrates intron splicing as a key step in intronic miR400 production and highlights the function of intronic miRNAs as a 'signal transducer' in enhancing plant stress tolerance.

The DEAD-box helicase RCF1 plays roles in miRNA biogenesis and RNA splicing in Arabidopsis

RCF1 is a highly conserved DEAD-box RNA helicase found in yeast, plants, and mammals. Studies about the functions of RCF1 in plants are limited. Here, we uncovered the functions of RCF1 in Arabidopsis thaliana as a player in pri-miRNA processing and splicing, as well as in pre-mRNA splicing. A mutant with miRNA biogenesis defects was isolated, and the defect was traced to a recessive point mutation in RCF1 (rcf1-4). We show that RCF1 promotes D-body formation and facilitates the interaction between pri-miRNAs and HYL1. Finally, we show that intron-containing pri-miRNAs and pre-mRNAs exhibit a global splicing defect in rcf1-4. Together, this work uncovers roles for RCF1 in miRNA biogenesis and RNA splicing in Arabidopsis.

SERRATE: a key factor in coordinated RNA processing in plants

The SERRATE (SE) protein is involved in the processing of RNA polymerase II (RNAPII) transcripts. It is associated with different complexes engaged in different aspects of plant RNA metabolism, including assemblies involved in transcription, splicing, polyadenylation, miRNA biogenesis, and RNA degradation. SE stability and interactome properties can be influenced by phosphorylation. SE exhibits an intriguing liquid-liquid phase separation property that may be important in the assembly of different RNA-processing bodies. Therefore, we propose that SE seems to participate in the coordination of different RNA-processing steps and can direct the fate of transcripts, targeting them for processing or degradation when they cannot be properly processed or are synthesized in excess.

Biogenesis, Mode of Action and the Interactions of Plant Non-Coding RNAs

The central dogma of genetics, which outlines the flow of genetic information from DNA to RNA to protein, has long been the guiding principle in molecular biology. In fact, more than three-quarters of the RNAs produced by transcription of the plant genome are not translated into proteins, and these RNAs directly serve as non-coding RNAs in the regulation of plant life activities at the molecular level. The breakthroughs in high-throughput transcriptome sequencing technology and the establishment and improvement of non-coding RNA experiments have now led to the discovery and confirmation of the biogenesis, mechanisms, and synergistic effects of non-coding RNAs. These non-coding RNAs are now predicted to play important roles in the regulation of gene expression and responses to stress and evolution. In this review, we focus on the synthesis, and mechanisms of non-coding RNAs, and we discuss their impact on gene regulation in plants.

Beyond transcription: compelling open questions in plant RNA biology

The study of RNAs has become one of the most influential research fields in contemporary biology and biomedicine. In the last few years, new sequencing technologies have produced an explosion of new and exciting discoveries in the field but have also given rise to many open questions. Defining these questions, together with old, long-standing gaps in our knowledge, is the spirit of this article. The breadth of topics within RNA biology research is vast, and every aspect of the biology of these molecules contains countless exciting open questions. Here, we asked 12 groups to discuss their most compelling question among some plant RNA biology topics. The following vignettes cover RNA alternative splicing; RNA dynamics; RNA translation; RNA structures; R-loops; epitranscriptomics; long non-coding RNAs; small RNA production and their functions in crops; small RNAs during gametogenesis and in cross-kingdom RNA interference; and RNA-directed DNA methylation. In each section, we will present the current state-of-the-art in plant RNA biology research before asking the questions that will surely motivate future discoveries in the field. We hope this article will spark a debate about the future perspective on RNA biology and provoke novel reflections in the reader.

MicroRNAs from Holarrhena pubescens stems: Identification by small RNA Sequencing and their Potential Contribution to Human Gene Targets

Holarrhena pubescens is an effective medicinal plant from the Apocynaceae family, widely distributed over the Indian subcontinent and extensively used by Ayurveda and ethno-medicine systems without apparent side effects. We postulated that miRNAs, endogenous non-coding small RNAs that regulate gene expression at the post-transcriptional level, may, after ingestion into the human body, contribute to the medicinal properties of plants of this species by inducing regulated human gene expression to modulate. However, knowledge is scarce about miRNA in Holarrhena. In addition, to test the hypothesis on the potential pharmacological properties of miRNA, we performed a high-throughput sequencing analysis using the Next Generation Sequencing Illumina platform; 42,755,236 raw reads have been generated from H. pubescens stems from a library of small RNA isolated, identifying 687 known and 50 new miRNAs led. The novel H. pubescens miRNAs were predicted to regulate specific human genes, and subsequent annotations of gene functions suggested a possible role in various biological processes and signaling pathways, such as Wnt, MAPK, PI3K-Akt, and AMPK signaling pathways and endocytosis. The association of these putative targets with many diseases, including cancer, congenital malformations, nervous system disorders, and cystic fibrosis, has been demonstrated. The top hub proteins STAT3, MDM2, GSK3B, NANOG, IGF1, PRKCA, SNAP25, SRSF1, HTT, and SNCA show their interaction with human diseases, including cancer and cystic fibrosis. To our knowledge, this is the first report of uncovering H. pubescens miRNAs based on high-throughput sequencing and bioinformatics analysis. This study has provided new insight into a potential cross-species control of human gene expression. The potential for miRNA transfer should be evaluated as one possible mechanism of action to account for the beneficial properties of this valuable species.

microRNA production in Arabidopsis

In plants, microRNAs (miRNAs) associate with ARGONAUTE (AGO) proteins and act as sequence-specific repressors of target gene expression, at the post-transcriptional level through target transcript cleavage and/or translational inhibition. MiRNAs are mainly transcribed by DNA-dependent RNA polymerase II (POL II) and processed by DICER LIKE1 (DCL1) complex into 21∼22 nucleotide (nt) long. Although the main molecular framework of miRNA biogenesis and modes of action have been established, there are still new requirements continually emerging in the recent years. The studies on the involvement factors in miRNA biogenesis indicate that miRNA biogenesis is not accomplished separately step by step, but is closely linked and dynamically regulated with each other. In this article, we will summarize the current knowledge on miRNA biogenesis, including MIR gene transcription, primary miRNA (pri-miRNA) processing, miRNA AGO1 loading and nuclear export; and miRNA metabolism including methylation, uridylation and turnover. We will describe how miRNAs are produced and how the different steps are regulated. We hope to raise awareness that the linkage between different steps and the subcellular regulation are becoming important for the understanding of plant miRNA biogenesis and modes of action.

Recent Insights into Plant miRNA Biogenesis: Multiple Layers of miRNA Level Regulation

MicroRNAs are small RNAs, 20-22 nt long, the main role of which is to downregulate gene expression at the level of mRNAs. MiRNAs are fundamental regulators of plant growth and development in response to internal signals as well as in response to abiotic and biotic factors. Therefore, the deficiency or excess of individual miRNAs is detrimental to particular aspects of a plant's life. In consequence, the miRNA levels must be appropriately adjusted. To obtain proper expression of each miRNA, their biogenesis is controlled at multiple regulatory layers. Here, we addressed processes discovered to influence miRNA steady-state levels, such as MIR transcription, co-transcriptional pri-miRNA processing (including splicing, polyadenylation, microprocessor assembly and activity) and miRNA-encoded peptides synthesis. MiRNA stability, RISC formation and miRNA export out of the nucleus and out of the plant cell also define the levels of miRNAs in various plant tissues. Moreover, we show the evolutionary conservation of miRNA biogenesis core proteins across the plant kingdom.

Chromatin-associated microprocessor assembly is regulated by the U1 snRNP auxiliary protein PRP40

In plants, microRNA (miRNA) biogenesis involves cotranscriptional processing of RNA polymerase II (RNAPII)-generated primary transcripts by a multi-protein complex termed the microprocessor. Here, we report that Arabidopsis (Arabidopsis thaliana) PRE-MRNA PROCESSING PROTEIN 40 (PRP40), the U1 snRNP auxiliary protein, positively regulates the recruitment of SERRATE, a core component of the plant microprocessor, to miRNA genes. The association of DICER-LIKE1 (DCL1), the microprocessor endoribonuclease, with chromatin was altered in prp40ab mutant plants. Impaired cotranscriptional microprocessor assembly was accompanied by RNAPII accumulation at miRNA genes and retention of miRNA precursors at their transcription sites in the prp40ab mutant plants. We show that cotranscriptional microprocessor assembly, regulated by AtPRP40, positively affects RNAPII transcription of miRNA genes and is important to reach the correct levels of produced miRNAs.

Arabidopsis AAR2, a conserved splicing factor in eukaryotes, acts in microRNA biogenesis

In yeast and humans, AAR2 is involved in pre-messenger RNA (pre-mRNA) splicing through regulating U5 snRNP assembly. This study shows that Arabidopsis AAR2 promotes microRNA (miRNA) accumulation in addition to its conserved role in pre-mRNA splicing. AAR2 is associated with the microprocessor component HYL1 and promotes its dephosphorylation to produce the active form in miRNA biogenesis. The study also reveals a previously unknown role of HYL1 in causing the degradation of the primary precursors to miRNAs (pri-miRNAs) and a role of AAR2 in protecting pri-miRNAs from HYL1-depedent degradation. Taken together, our findings provide insights into the role of a conserved splicing factor in miRNA biogenesis in plants.

MicroRNAs (miRNAs) play an essential role in plant growth and development, and as such, their biogenesis is fine-tuned via regulation of the core microprocessor components. Here, we report that Arabidopsis AAR2, a homolog of a U5 snRNP assembly factor in yeast and humans, not only acts in splicing but also promotes miRNA biogenesis. AAR2 interacts with the microprocessor component hyponastic leaves 1 (HYL1) in the cytoplasm, nucleus, and dicing bodies. In aar2 mutants, abundance of nonphosphorylated HYL1, the active form of HYL1, and the number of HYL1-labeled dicing bodies are reduced. Primary miRNA (pri-miRNA) accumulation is compromised despite normal promoter activities of MIR genes in aar2 mutants. RNA decay assays show that the aar2-1 mutation leads to faster degradation of pri-miRNAs in a HYL1-dependent manner, which reveals a previously unknown and negative role of HYL1 in miRNA biogenesis. Taken together, our findings reveal a dual role of AAR2 in miRNA biogenesis and pre-messenger RNA splicing.

Transcriptional and post-transcriptional regulation of RNAi-related gene expression during plant-virus interactions

As sessile organisms, plants encounter diverse invasions from pathogens including viruses. To survive and thrive, plants have evolved multilayered defense mechanisms to combat virus infection. RNAi, also known as RNA silencing, is an across-kingdom innate immunity and gene regulatory machinery. Molecular framework and crucial roles of RNAi in antiviral defense have been well-characterized. However, it is largely unknown that how RNAi is transcriptionally regulated to initiate, maintain and enhance cellular silencing under normal or stress conditions. Recently, insights into the transcriptional and post-transcriptional regulation of RNAi-related genes in different physiological processes have been emerging. In this review, we integrate these new findings to provide updated views on how plants modulate RNAi machinery at the (post-) transcriptional level to respond to virus infection.

Biogenesis, conservation, and function of miRNA in liverworts

MicroRNAs (miRNAs) are small non-coding endogenous RNA molecules, 18-24 nucleotides long, that control multiple gene regulatory pathways via post-transcriptional gene silencing in eukaryotes. To develop a comprehensive picture of the evolutionary history of miRNA biogenesis and action in land plants, studies on bryophyte representatives are needed. Here, we review current understanding of liverwort MIR gene structure, miRNA biogenesis, and function, focusing on the simple thalloid Pellia endiviifolia and the complex thalloid Marchantia polymorpha. We review what is known about conserved and non-conserved miRNAs, their targets, and the functional implications of miRNA action in M. polymorpha and P. endiviifolia. We note that most M. polymorpha miRNAs are encoded within protein-coding genes and provide data for 23 MIR gene structures recognized as independent transcriptional units. We identify M. polymorpha genes involved in miRNA biogenesis that are homologous to those identified in higher plants, including those encoding core microprocessor components and other auxiliary and regulatory proteins that influence the stability, folding, and processing of pri-miRNAs. We analyzed miRNA biogenesis proteins and found similar domain architecture in most cases. Our data support the hypothesis that almost all miRNA biogenesis factors in higher plants are also present in liverworts, suggesting that they emerged early during land plant evolution.

The Importance of a Genome-Wide Association Analysis in the Study of Alternative Splicing Mutations in Plants with a Special Focus on Maize

Alternative splicing is an important mechanism for regulating gene expressions at the post-transcriptional level. In eukaryotes, the genes are transcribed in the nucleus to produce pre-mRNAs and alternative splicing can splice a pre-mRNA to eventually form multiple different mature mRNAs, greatly increasing the number of genes and protein diversity. Alternative splicing is involved in the regulation of various plant life activities, especially the response of plants to abiotic stresses and is also an important process of plant growth and development. This review aims to clarify the usefulness of a genome-wide association analysis in the study of alternatively spliced variants by summarizing the application of alternative splicing, genome-wide association analyses and genome-wide association analyses in alternative splicing, as well as summarizing the related research progress.

MiRNA fine tuning for crop improvement: using advance computational models and biotechnological tools

MiRNAs modulate target genes expression at post-transcriptional levels, by reducing spatial abundance of mRNAs. MiRNAs regulats plant metabolism, and emerged as regulators of plant stress responses. Which make miRNAs promising candidates for fine tuning to affectively alter crop stress tolerance and other important traits. With recent advancements in the computational biology and biotechnology miRNAs structure and target prediction is possible resulting in pin point editing; miRNA modulation can be done by up or down regulating miRNAs using recently available biotechnological tools (CRISPR Cas9, TALENS and RNAi). In this review we have focused on miRNA biogenesis, miRNA roles in plant development, plant stress responses and roles in signaling pathways. Additionally we have discussed latest computational prediction models for miRNA to target gene interaction and biotechnological systems used recently for miRNA modulation. We have also highlighted setbacks and limitations in the way of miRNA modulation; providing entirely a new direction for improvement in plant genomics primarily focusing miRNAs.

Noncoding RNAs in Drug Resistance of Gastrointestinal Stromal Tumor

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor in the gastrointestinal tracts and a model for the targeted therapy of solid tumors because of the oncogenic driver mutations in KIT and PDGDRA genes, which could be effectively inhibited by the very first targeted agent, imatinib mesylate. Most of the GIST patients could benefit a lot from the targeted treatment of this receptor tyrosine kinase inhibitor. However, more than 50% of the patients developed resistance within 2 years after imatinib administration, limiting the long-term effect of imatinib. Noncoding RNAs (ncRNAs), the non-protein coding transcripts of human, were demonstrated to play pivotal roles in the resistance of various chemotherapy drugs. In this review, we summarized the mechanisms of how ncRNAs functioning on the drug resistance in GIST. During the drug resistance of GIST, there were five regulating mechanisms where the functions of ncRNAs concentrated: oxidative phosphorylation, autophagy, apoptosis, drug target changes, and some signaling pathways. Also, these effects of ncRNAs in drug resistance were divided into two aspects. How ncRNAs regulate drug resistance in GIST was further summarized according to ncRNA types, different drugs and categories of resistance. Moreover, clinical applications of these ncRNAs in GIST chemotherapies concentrated on the prognostic biomarkers and novel therapeutic targets.

Identification of microRNAs from Medicinal Plant Murraya koenigii by High-Throughput Sequencing and Their Functional Implications in Secondary Metabolite Biosynthesis

MicroRNAs (miRNAs) are small noncoding RNA molecules that play crucial post-transcriptional regulatory roles in plants, including development and stress-response signaling. However, information about their involvement in secondary metabolism is still limited. Murraya koenigii is a popular medicinal plant, better known as curry leaves, that possesses pharmaceutically active secondary metabolites. The present study utilized high-throughput sequencing technology to investigate the miRNA profile of M. koenigii and their association with secondary metabolite biosynthesis. A total of 343,505 unique reads with lengths ranging from 16 to 40 nt were obtained from the sequencing data, among which 142 miRNAs were identified as conserved and 7 as novel miRNAs. Moreover, 6078 corresponding potential target genes of M. koenigii miRNAs were recognized in this study. Interestingly, several conserved and novel miRNAs of M. koenigii were found to target key enzymes of the terpenoid backbone and the flavonoid biosynthesis pathways. Furthermore, to validate the sequencing results, the relative expression of eight randomly selected miRNAs was determined by qPCR. To the best of our knowledge, this is the first report of the M. koenigii miRNA profile that may provide useful information for further elucidation of the involvement of miRNAs in secondary metabolism. These findings might be crucial in the future to generate artificial-miRNA-based, genetically engineered M. koenigii plants for the overproduction of medicinally highly valuable secondary metabolites.

MicroRNA-mediated bioengineering for climate-resilience in crops

Global projections on the climate change and the dynamic environmental perturbations indicate severe impacts on food security in general, and crop yield, vigor and the quality of produce in particular. Sessile plants respond to environmental challenges such as salt, drought, temperature, heavy metals at transcriptional and/or post-transcriptional levels through the stress-regulated network of pathways including transcription factors, proteins and the small non-coding endogenous RNAs. Amongs these, the miRNAs have gained unprecedented attention in recent years as key regulators for modulating gene expression in plants under stress. Hence, tailoring of miRNAs and their target pathways presents a promising strategy for developing multiple stress-tolerant crops. Plant stress tolerance has been successfully achieved through the over expression of microRNAs such as Os-miR408, Hv-miR82 for drought tolerance; OsmiR535A and artificial DST miRNA for salinity tolerance; and OsmiR535 and miR156 for combined drought and salt stress. Examples of miR408 overexpression also showed improved efficiency of irradiation utilization and carbon dioxide fixation in crop plants. Through this review, we present the current understanding about plant miRNAs, their roles in plant growth and stress-responses, the modern toolbox for identification, characterization and validation of miRNAs and their target genes including in silico tools, machine learning and artificial intelligence. Various approaches for up-regulation or knock-out of miRNAs have been discussed. The main emphasis has been given to the exploration of miRNAs for development of bioengineered climate-smart crops that can withstand changing climates and stressful environments, including combination of stresses, with very less or no yield penalties.

Serrate-Associated Protein 1, a splicing-related protein, promotes miRNA biogenesis in Arabidopsis

MicroRNAs (miRNAs) are essential regulators of gene expression in metazoans and plants. In plants, most miRNAs are generated from primary miRNA transcripts (pri-miRNAs), which are processed by the Dicer-like 1 (DCL1) complex along with accessory proteins. Serrate-Associated Protein 1 (SEAP1), a conserved splicing-related protein, has been studied in human and yeast. However, the functions of SEAP1 in plants remain elusive. Lack of SEAP1 results in embryo lethality and knockdown of SEAP1 by an artificial miRNA (amiR^SEAP1 ) causes pleiotropic developmental defects and reduction in miRNA accumulation. SEAP1 associates with the DCL1 complex, and may promote the interaction of the DCL1 complexes with pri-miRNAs. SEAP1 also enhances pri-miRNA accumulation, but does not affect pri-miRNA transcription, suggesting it may indirectly or directly stabilize pri-miRNAs. In addition, SEAP1 affects the splicing of some pri-miRNAs and intron retention of messenger RNAs at global levels. Our findings uncover both conserved and novel functions of SEAP1 in plants. Besides the role as a splicing factor, SEPA1 may promote miRNA biogenesis by positively modulating pri-miRNA splicing, processing and/or stability.

Comparative analysis identifies micro-RNA associated with nutrient homeostasis, development and stress response in Arabidopsis thaliana upon high Zn and metal hyperaccumulator Arabidopsis halleri

miRNAs have been found to be key players in mineral homeostasis, both in the control of nutrient balance and in the response to toxic trace elements. However, the effect of Zn excess on miRNAs has not been elucidated; moreover, no data are present regarding miRNAs in hyperaccumulator species, where metal homeostasis is tightly regulated. Therefore, expression levels of mature miRNAs were measured by RNA-Seq in Zn-sensitive Arabidopsis thaliana grown in control conditions and upon high Zn, in soil and in Zn-hyperaccumulator Arabidopsis halleri grown in control conditions. Differential expression of notable miRNAs and their targets was confirmed by real-time RT-PCR. The comparison in A. thaliana revealed a small subset modulated upon Zn treatment that is associated with stress response and nutrient homeostasis. On the other hand, a more consistent group of miRNAs was differentially expressed in A. halleri compared with A. thaliana, reflecting inherent differences in nutritional requirements and response to stresses and plant growth and development. Overall, these results confirm the involvement of miRNAs in Zn homeostasis and support the hypothesis of distinct regulatory pathways in hyperaccumulator species.

Nitric oxide, crosstalk with stress regulators and plant abiotic stress tolerance

Nitric oxide is a dynamic gaseous molecule involved in signalling, crosstalk with stress regulators, and plant abiotic-stress responses. It has great exploratory potentials for engineering abiotic stress tolerance in crops. Nitric oxide (NO), a redox-active gaseous signalling molecule, though present uniformly through the eukaryotes, maintain its specificity in plants with respect to its formation, signalling, and functions. Its cellular concentrations are decisive for its function, as a signalling molecule at lower concentrations, but triggers nitro-oxidative stress and cellular damage when produced at higher concentrations. Besides, it also acts as a potent stress alleviator. Discovered in animals as neurotransmitter, NO has come a long way to being a stress radical and growth regulator in plants. As a key redox molecule, it exhibits several key cellular and molecular interactions including with reactive chemical species, hydrogen sulphide, and calcium. Apart from being a signalling molecule, it is emerging as a key player involved in regulations of plant growth, development and plant-environment interactions. It is involved in crosstalk with stress regulators and is thus pivotal in these stress regulatory mechanisms. NO is getting an unprecedented attention from research community, being investigated and explored for its multifaceted roles in plant abiotic stress tolerance. Through this review, we intend to present the current knowledge and updates on NO biosynthesis and signalling, crosstalk with stress regulators, and how biotechnological manipulations of NO pathway are leading towards developing transgenic crop plants that can withstand environmental stresses and climate change. The targets of various stress responsive miRNA signalling have also been discussed besides giving an account of current approaches used to characterise and detect the NO.

Waterlogging-Stress-Responsive LncRNAs, Their Regulatory Relationships with miRNAs and Target Genes in Cucumber (Cucumis sativus L.)

Low oxygen level is a phenomenon often occurring during the cucumber cultivation period. Genes involved in adaptations to stress can be regulated by non-coding RNA. The aim was the identification of long non-coding RNAs (lncRNAs) involved in the response to long-term waterlogging stress in two cucumber haploid lines, i.e., DH2 (waterlogging tolerant—WL-T) and DH4 (waterlogging sensitive—WL-S). Plants, at the juvenile stage, were waterlogged for 7 days (non-primed, 1xH), and after a 14-day recovery period, plants were stressed again for another 7 days (primed, 2xH). Roots were collected for high-throughput RNA sequencing. Implementation of the bioinformatic pipeline made it possible to determine specific lncRNAs for non-primed and primed plants of both accessions, highlighting differential responses to hypoxia stress. In total, 3738 lncRNA molecules were identified. The highest number (1476) of unique lncRNAs was determined for non-primed WL-S plants. Seventy-one lncRNAs were depicted as potentially being involved in acquiring tolerance to hypoxia in cucumber. Understanding the mechanism of gene regulation under long-term waterlogging by lncRNAs and their interactions with miRNAs provides sufficient information in terms of adaptation to the oxygen deprivation in cucumber. To the best of our knowledge, this is the first report concerning the role of lncRNAs in the regulation of long-term waterlogging tolerance by priming application in cucumber.

MicroRNAs in Apple-Derived Nanoparticles Modulate Intestinal Expression of Organic Anion-Transporting Peptide 2B1/SLCO2B1 in Caco-2 Cells

Plant-derived nanoparticles exert cytoprotective effects on intestinal cells by delivering their cargo to intestinal tissues. We previously reported that apple-derived nanoparticles (APNPs) downregulate the mRNA of the human intestinal transporter organic anion-transporting peptide 2B1 (OATP2B1)/SLCO2B1 and that the 3'-untranslated region (3'UTR) is required for the response to APNPs. Here, we investigated the involvement of microRNAs (miRNAs) in APNPs in suppressing OATP2B1 expression to demonstrate that APNP macromolecules directly interact with intestinal tissues. Using in silico analysis, seven apple miRNAs were predicted as candidate miRNAs that interact with the SLCO2B1-3'UTR. The APNP-mediated decrease in luciferase activity of pGL3/SLCO2B1-3'UTR was abrogated by inhibitors of mdm-miR-160a-e, -7121a-c, or -7121d-h. Each miRNA mimic reduced the endogenous expression of SLCO2B1 mRNA in Caco-2 cells. The luciferase activity of the truncated pGL3/SLCO2B1-3'UTR, which contains approximately 200 bp around each miRNA recognition element (MRE), was decreased by the miR-7121d-h mimic but decreased little by the other mimics. APNP also reduced the luciferase activity of truncated pGL3/SLCO2B1-3'UTR containing an MRE for miR-7121d-h. Thus, we demonstrated that mdm-miR-7121d-h contributes to the APNP-mediated downregulation of intestinal OATP2B1. Accordingly, plant macromolecules, such as miRNAs, may directly interact with intestinal tissues via nanoparticles. SIGNIFICANCE STATEMENT: This study demonstrates that mdm-miR7121d-h contained in apple-derived nanoparticles downregulated the mRNA expression of SLCO2B1 by interacting with SLCO2B1-3'-untranslated region directly and that SLCO2B1 mRNA might also be decreased by mdm-miR160a-e and -7121a-c indirectly. This finding that the specific apple-derived microRNAs influence human intestinal transporters provides a novel concept that macromolecules in foods directly interact with and affect the intestinal function of the host.

MicroRNA‑193a‑5p exerts a tumor suppressive role in epithelial ovarian cancer by modulating RBBP6

Epithelial ovarian cancer (EOC), a gynecological tumor, is associated with high mortality. MicroRNAs (miRs) serve a crucial role in EOC; however, the mechanisms underlying the effect of miRNA-193a-5p in EOC are not completely understood. Therefore, the present study aimed to investigate the expression levels of miR-193a-5p in serum samples of patients with EOC and to determine the role of miR-193a-5p in EOC. Reverse transcription-quantitative PCR was used to analyze the expression levels of miR-193a-5p in serum samples of patients with EOC and EOC cell lines. The effects of miR-193a-5p and RB binding protein 6, ubiquitin ligase (RBBP6) on the biological functions of EOC were determined by conducting a series of in vitro cell function experiments. The results indicated that the expression levels of miR-193a-5p were significantly decreased in serum samples obtained from patients with EOC and EOC cell lines compared with healthy individuals and normal cells, respectively. Further investigations indicated that RBBP6 was a target gene of miR-193a-5p. The expression levels of RBBP6 were significantly increased in patients with EOC compared with healthy individuals. In addition, in vitro analysis suggested that miR-193a-5p mimic significantly decreased SKOV3 cell proliferation, migration and invasion, and promoted SKOV3 cell apoptosis compared with the control and mimic-negative control groups. In addition, RBBP6 overexpression reversed miR-193a-5p mimic-mediated effects. In conclusion, the results of the present study suggested that downregulated expression levels of miR-193a-5p may serve an inhibitory role in EOC by inhibiting cell proliferation and metastasis, and promoting apoptosis.

Regulation of pri-MIRNA processing: mechanistic insights into the miRNA homeostasis in plant

miRNAs in plant plays crucial role in controlling proper growth, development and fitness by modulating the expression of their target genes. Therefore to modulate the expression of any stress/development related gene specifically, it is better to modulate expression of the miRNA that can target that gene. To modulate the expression level of miRNA, it is prerequisite to uncover the underlying molecular mechanism of its biogenesis. The biogenesis pathway consists of two major steps, transcription of MIR gene to pri-MIRNA and processing of pri-MIRNA into mature miRNA via sequential cleavage steps. Both of these pathways are tightly controlled by several different factors involving structural and functional molecules. This review is mainly focused on different aspects of pri-MIRNA processing mechanism to emphasize on the fact that to modulate the level of a miRNA in the cell only over-expression or knock-down of that MIR gene is not always sufficient rather it is also crucial to take processing regulation into consideration. The data collected from the recent and relevant literatures depicts that processing regulation is controlled by several aspects like structure and size of the pri-MIRNA, presence of introns in MIR gene and their location, interaction of processing factors with the core components of processing machinery etc. These detailed information can be utilized to figure out the particular point which can be utilized to modulate the expression of the miRNA which would ultimately be beneficial for the scientist and researcher working in this field to generate protocol for engineering plant with improved yield and stress tolerance.

Differential Epigenetic Marks Are Associated with Apospory Expressivity in Diploid Hybrids of Paspalum rufum

Apomixis seems to emerge from the deregulation of preexisting genes involved in sexuality by genetic and/or epigenetic mechanisms. The trait is associated with polyploidy, but diploid individuals of Paspalum rufum can form aposporous embryo sacs and develop clonal seeds. Moreover, diploid hybrid families presented a wide apospory expressivity variation. To locate methylation changes associated with apomixis expressivity, we compare relative DNA methylation levels, at CG, CHG, and CHH contexts, between full-sib P. rufum diploid genotypes presenting differential apospory expressivity. The survey was performed using a methylation content-sensitive enzyme ddRAD (MCSeEd) strategy on samples at premeiosis/meiosis and postmeiosis stages. Based on the relative methylation level, principal component analysis and heatmaps, clearly discriminate samples with contrasting apospory expressivity. Differential methylated contigs (DMCs) showed 14% of homology to known transcripts of Paspalum notatum reproductive transcriptome, and almost half of them were also differentially expressed between apomictic and sexual samples. DMCs showed homologies to genes involved in flower growth, development, and apomixis. Moreover, a high proportion of DMCs aligned on genomic regions associated with apomixis in Setaria italica. Several stage-specific differential methylated sequences were identified as associated with apospory expressivity, which could guide future functional gene characterization in relation to apomixis success at diploid and tetraploid levels.

Processing of coding and non-coding RNAs in plant development and environmental responses

Precursor RNAs undergo extensive processing to become mature RNAs. RNA transcripts are subjected to 5′ capping, 3′-end processing, splicing, and modification; they also form dynamic secondary structures during co-transcriptional and post-transcriptional processing. Like coding RNAs, non-coding RNAs (ncRNAs) undergo extensive processing. For example, secondary small interfering RNA (siRNA) transcripts undergo RNA processing, followed by further cleavage to become mature siRNAs. Transcriptome studies have revealed roles for co-transcriptional and post-transcriptional RNA processing in the regulation of gene expression and the coordination of plant development and plant–environment interactions. In this review, we present the latest progress on RNA processing in gene expression and discuss phased siRNAs (phasiRNAs), a kind of germ cell-specific secondary small RNA (sRNA), focusing on their functions in plant development and environmental responses.

Barley microRNAs as metabolic sensors for soil nitrogen availability

Barley (Hordeum vulgare) is one of the most important crops in the world, ranking 4th in the worldwide production. Crop breeders are facing increasing environmental obstacles in the field, such as drought, salinity but also toxic over fertilization which not only impacts quality of the grain but also an yield. One of the most prevalent mechanisms of gene expression regulation in plants is microRNA-mediated silencing of target genes. We identified 13 barley microRNAs and 2 microRNAs* that are nitrogen excess responsive. Four microRNAs respond only in root, eight microRNAs only in shoot and one displays broad response in roots and shoots. We demonstrate that 2 microRNAs* are induced in barley shoot by nitrogen excess. For all microRNAs we identified putative target genes and confirmed microRNA-guided cleavage sites for ten out of thirteen mRNAs. None of the identified microRNAs or their target genes is known as nitrogen excess responsive. Analysis of expression pattern of thirteen target mRNAs and their cognate microRNAs showed expected correlations of their levels. The plant microRNAs analyzed are also known to respond to nitrogen deprivation and exhibit the opposite expression pattern when nitrogen excess/deficiency conditions are compared. Thus, they can be regarded as metabolic sensors of the regulation of nitrogen homeostasis in plants.

Quantitative Analysis of Plant miRNA Primary Transcripts

MicroRNAs control plant development and are key regulators of plant responses to biotic and abiotic stresses. Thus, their expression must be carefully controlled since both excess and deficiency of a given microRNA may be deleterious to plant cell. MicroRNA expression regulation can occur at several stages of their biogenesis pathway. One of the most important of these regulatory checkpoints is transcription efficiency. mirEX database is a tool for exploration and visualization of plant pri-miRNA expression profiles. It includes results obtained using high-throughput RT-qPCR platform designed to monitor pri-miRNA expression in different miRNA biogenesis mutants and developmental stages of Arabidopsis, barley, and Pellia plants. A step-by-step instruction for browsing the database and detailed protocol for high-throughput RT-qPCR experiments, including list of primers designed for the amplification of pri-miRNAs, are presented.

Core spliceosomal Sm proteins as constituents of cytoplasmic mRNPs in plants

In recent years, research has increasingly focused on the key role of post-transcriptional regulation of messenger ribonucleoprotein (mRNP) function and turnover. As a result of the complexity and dynamic nature of mRNPs, the full composition of a single mRNP complex remains unrevealed and mRNPs are poorly described in plants. Here we identify canonical Sm proteins as part of the cytoplasmic mRNP complex, indicating their function in the post-transcriptional regulation of gene expression in plants. Sm proteins comprise an evolutionarily ancient family of small RNA-binding proteins involved in pre-mRNA splicing. The latest research indicates that Sm could also impact on mRNA at subsequent stages of its life cycle. In this work we show that in the microsporocyte cytoplasm of Larix decidua, the European larch, Sm proteins accumulate within distinct cytoplasmic bodies, also containing polyadenylated RNA. To date, several types of cytoplasmic bodies involved in the post-transcriptional regulation of gene expression have been described, mainly in animal cells. Their role and molecular composition in plants remain less well established, however. A total of 222 mRNA transcripts have been identified as cytoplasmic partners for Sm proteins. The specific colocalization of these mRNAs with Sm proteins within cytoplasmic bodies has been confirmed via microscopic analysis. The results from this work support the hypothesis, that evolutionarily conserved Sm proteins have been adapted to perform a whole repertoire of functions related to the post-transcriptional regulation of gene expression in Eukaryota. This adaptation presumably enabled them to coordinate the interdependent processes of splicing element assembly, mRNA maturation and processing, and mRNA translation regulation, and its degradation.

Insights into the N6-methyladenosine mechanism and its functionality: progress and questions

N⁶-methyladenosine (m6A) RNA methylation has become a progressively popular area of molecular research since the discovery of its potentially essential regulatory role amongst eukaryotes. m6A marks are observed in the 5'UTR, 3'UTR and coding regions of eukaryotes and its mediation has been associated with various human diseases, RNA stability and translational efficiency. To understand the implications of m6A methylation in molecular governance, its functionality and mechanism must be initially understood. m6A regulation through its readers, writers and erasers as well as an insight into the potential "cross-talk" occurring between m6A and previously well documented regulatory molecular mechanisms have been characterized. The majority of research to date has been limited to few species and has yet to explore the species- and tissue specific nature or mechanistic plasticity of m6A regulation. There is still a tremendous gap in our knowledge surrounding the mechanism and functionality of m6A RNA methylation. Here we review the formation, removal, and decoding of m6A amongst animals, yeast, and plants while noting potential "cross-talk" between various mechanisms and highlighting potential areas of future research.

Emerging role of tumor-related functional peptides encoded by lncRNA and circRNA

Non-coding RNAs do not encode proteins and regulate various oncological processes. They are also important potential cancer diagnostic and prognostic biomarkers. Bioinformatics and translation omics have begun to elucidate the roles and modes of action of the functional peptides encoded by ncRNA. Here, recent advances in long non-coding RNA (lncRNA) and circular RNA (circRNA)-encoded small peptides are compiled and synthesized. We introduce both the computational and analytical methods used to forecast prospective ncRNAs encoding oncologically functional oligopeptides. We also present numerous specific lncRNA and circRNA-encoded proteins and their cancer-promoting or cancer-inhibiting molecular mechanisms. This information may expedite the discovery, development, and optimization of novel and efficacious cancer diagnostic, therapeutic, and prognostic protein-based tools derived from non-coding RNAs. The role of ncRNA-encoding functional peptides has promising application perspectives and potential challenges in cancer research. The aim of this review is to provide a theoretical basis and relevant references, which may promote the discovery of more functional peptides encoded by ncRNAs, and further develop novel anticancer therapeutic targets, as well as diagnostic and prognostic cancer markers.

SMA1, a homolog of the splicing factor Prp28, has a multifaceted role in miRNA biogenesis in Arabidopsis

MicroRNAs (miRNAs) are a class of small non-coding RNAs that repress gene expression. In plants, the RNase III enzyme Dicer-like (DCL1) processes primary miRNAs (pri-miRNAs) into miRNAs. Here, we show that SMALL1 (SMA1), a homolog of the DEAD-box pre-mRNA splicing factor Prp28, plays essential roles in miRNA biogenesis in Arabidopsis. A hypomorphic sma1-1 mutation causes growth defects and reduces miRNA accumulation correlated with increased target transcript levels. SMA1 interacts with the DCL1 complex and positively influences pri-miRNA processing. Moreover, SMA1 binds the promoter region of genes encoding pri-miRNAs (MIRs) and is required for MIR transcription. Furthermore, SMA1 also enhances the abundance of the DCL1 protein levels through promoting the splicing of the DCL1 pre-mRNAs. Collectively, our data provide new insights into the function of SMA1/Prp28 in regulating miRNA abundance in plants.

Efficiency and precision of microRNA biogenesis modes in plants

Many evolutionarily conserved microRNAs (miRNAs) in plants regulate transcription factors with key functions in development. Hence, mutations in the core components of the miRNA biogenesis machinery cause strong growth defects. An essential aspect of miRNA biogenesis is the precise excision of the small RNA from its precursor. In plants, miRNA precursors are largely variable in size and shape and can be processed by different modes. Here, we optimized an approach to detect processing intermediates during miRNA biogenesis. We characterized a miRNA whose processing is triggered by a terminal branched loop. Plant miRNA processing can be initiated by internal bubbles, small terminal loops or branched loops followed by dsRNA segments of 15–17 bp. Interestingly, precision and efficiency vary with the processing modes. Despite the various potential structural determinants present in a single a miRNA precursor, DCL1 is mostly guided by a predominant structural region in each precursor in wild-type plants. However, our studies in fiery1, hyl1 and se mutants revealed the existence of cleavage signatures consistent with the recognition of alternative processing determinants. The results provide a general view of the mechanisms underlying the specificity of miRNA biogenesis in plants.

Micromanagement of Developmental and Stress-Induced Senescence: The Emerging Role of MicroRNAs

MicroRNAs are short (19⁻24-nucleotide-long), non-coding RNA molecules. They downregulate gene expression by triggering the cleavage or translational inhibition of complementary mRNAs. Senescence is a stage of development following growth completion and is dependent on the expression of specific genes. MicroRNAs control the gene expression responsible for plant competence to answer senescence signals. Therefore, they coordinate the juvenile-to-adult phase transition of the whole plant, the growth and senescence phase of each leaf, age-related cellular structure changes during vessel formation, and remobilization of resources occurring during senescence. MicroRNAs are also engaged in the ripening and postharvest senescence of agronomically important fruits. Moreover, the hormonal regulation of senescence requires microRNA contribution. Environmental cues, such as darkness or drought, induce senescence-like processes in which microRNAs also play regulatory roles. In this review, we discuss recent findings concerning the role of microRNAs in the senescence of various plant species.

Cold-Dependent Expression and Alternative Splicing of Arabidopsis Long Non-coding RNAs

Plants re-program their gene expression when responding to changing environmental conditions. Besides differential gene expression, extensive alternative splicing (AS) of pre-mRNAs and changes in expression of long non-coding RNAs (lncRNAs) are associated with stress responses. RNA-sequencing of a diel time-series of the initial response of Arabidopsis thaliana rosettes to low temperature showed massive and rapid waves of both transcriptional and AS activity in protein-coding genes. We exploited the high diversity of transcript isoforms in AtRTD2 to examine regulation and post-transcriptional regulation of lncRNA gene expression in response to cold stress. We identified 135 lncRNA genes with cold-dependent differential expression (DE) and/or differential alternative splicing (DAS) of lncRNAs including natural antisense RNAs, sORF lncRNAs, and precursors of microRNAs (miRNAs) and trans-acting small-interfering RNAs (tasiRNAs). The high resolution (HR) of the time-series allowed the dynamics of changes in transcription and AS to be determined and identified early and adaptive transcriptional and AS changes in the cold response. Some lncRNA genes were regulated only at the level of AS and using plants grown at different temperatures and a HR time-course of the first 3 h of temperature reduction, we demonstrated that the AS of some lncRNAs is highly sensitive to small temperature changes suggesting tight regulation of expression. In particular, a splicing event in TAS1a which removed an intron that contained the miR173 processing and phased siRNAs generation sites was differentially alternatively spliced in response to cold. The cold-induced reduction of the spliced form of TAS1a and of the tasiRNAs suggests that splicing may enhance production of the siRNAs. Our results identify candidate lncRNAs that may contribute to the regulation of expression that determines the physiological processes essential for acclimation and freezing tolerance.

Identification and expression analysis of a microRNA cluster derived from pre-ribosomal RNA in Papaver somniferum L. and Papaver bracteatum L

Opium poppy (Papaver somniferum L.) is one of the ancient medical crops, which produces several important alkaloids such as morphine, noscapine, sanguinarine and codeine. MicroRNAs are endogenous non-coding RNAs that play important regulatory roles in plant diverse biological processes. Many plant miRNAs are encoded as single transcriptional units, in contrast to animal miRNAs, which are often clustered. Herein, using computational approaches, a total of 22 miRNA precursors were identified, which five of them were located as a clustered in pre-ribosomal RNA. Afterward, the transcript level of the precursor and the mature of clustered miRNAs in two species of the Papaveraceae family, i.e. P. somniferum L. and P. bracteatum L, were quantified by RT-PCR. With respect to obtained results, these clustered miRNAs were expressed differentially in different tissues of these species. Moreover, using target prediction and Gene Ontology (GO)-based on functional classification indicated that these miRNAs might play crucial roles in various biological processes as well as metabolic pathways. In this study, we discovered the clustered miRNA derived from pre-rRNA, which may shed some light on the importance of miRNAs in the plant kingdom.

Discovering Structural Motifs in miRNA Precursors from the Viridiplantae Kingdom

A small non-coding molecule of microRNA (19–24 nt) controls almost every biological process, including cellular and physiological, of various organisms’ lives. The amount of microRNA (miRNA) produced within an organism is highly correlated to the organism’s key processes, and determines whether the system works properly or not. A crucial factor in plant biogenesis of miRNA is the Dicer Like 1 (DCL1) enzyme. Its responsibility is to perform the cleavages in the miRNA maturation process. Despite everything we already know about the last phase of plant miRNA creation, recognition of miRNA by DCL1 in pre-miRNA structures of plants remains an enigma. Herein, we present a bioinformatic procedure we have followed to discover structure patterns that could guide DCL1 to perform a cleavage in front of or behind an miRNA:miRNA* duplex. The patterns in the closest vicinity of microRNA are searched, within pre-miRNA sequences, as well as secondary and tertiary structures. The dataset consists of structures of plant pre-miRNA from the Viridiplantae kingdom. The results confirm our previous observations based on Arabidopsis thaliana precursor analysis. Hereby, our hypothesis was tested on pre-miRNAs, collected from the miRBase database to show secondary structure patterns of small symmetric internal loops 1-1 and 2-2 at a 1–10 nt distance from the miRNA:miRNA* duplex.

Structural analysis of human ARS2 as a platform for co-transcriptional RNA sorting

ARS2 is a highly conserved metazoan protein involved in numerous aspects of nuclear RNA metabolism. As a direct partner of the nuclear cap-binding complex (CBC), it mediates interactions with diverse RNA processing and transport machineries in a transcript-dependent manner. Here, we present the human ARS2 crystal structure, which exhibits similarities and metazoan-specific differences to the plant homologue SERRATE, most notably an additional RRM domain. We present biochemical, biophysical and cellular interactome data comparing wild type and mutant ARS2 that identify regions critical for interactions with FLASH (involved in histone mRNA biogenesis), NCBP3 (a putative cap-binding protein involved in mRNA export) and single-stranded RNA. We show that FLASH and NCBP3 have overlapping binding sites on ARS2 and that CBC–ARS2–NCBP3 form a ternary complex that is mutually exclusive with CBC–ARS–PHAX (involved in snRNA export). Our results support that mutually exclusive higher-order CBC–ARS2 complexes are critical in determining Pol II transcript fate.

Arsenic resistance protein 2 (ARS2) plays an important role in nuclear RNA metabolism and interacts with the nuclear cap-binding complex (CBC). Here the authors present the human ARS2 structure and identify regions important for its interactions with binding partners supporting that mutually exclusive higher order CBC-ARS2 complexes are formed.

Plant microRNAs: Front line players against invading pathogens

Plants are attacked by a large number of pathogens. To defend against these pathogens, plants activate or repress a vast array of genes. For genetic expression and reprogramming, host endogenous small RNAs (sRNAs) are the key factors. Among these sRNAs, microRNAs (miRNAs) mediate gene regulation through RNA silencing at the post-transcriptional level and play an essential role in the defense responses to biotic and abiotic stress. In the recent years, high-throughput sequencing has enabled the researchers to uncover the role of plant miRNAs during pathogen invasion. So here we have reviewed the recent research findings illustrating the plant miRNAs active involvement in various defense processes during fungal, bacterial, viral and nematode infections. However, rapid validation of direct targets of miRNAs is the dire need of time, which can be very helpful in improving the plant resistance against various pathogenic diseases.

Regulation of Plant Microprocessor Function in Shaping microRNA Landscape

MicroRNAs are small molecules (∼21 nucleotides long) that are key regulators of gene expression. They originate from long stem-loop RNAs as a product of cleavage by a protein complex called Microprocessor. The core components of the plant Microprocessor are the RNase type III enzyme Dicer-Like 1 (DCL1), the zinc finger protein Serrate (SE), and the double-stranded RNA binding protein Hyponastic Leaves 1 (HYL1). Microprocessor assembly and its processing of microRNA precursors have been reported to occur in discrete nuclear bodies called Dicing bodies. The accessibility of and modifications to Microprocessor components affect microRNA levels and may have dramatic consequences in plant development. Currently, numerous lines of evidence indicate that plant Microprocessor activity is tightly regulated. The cellular localization of HYL1 is dependent on a specific KETCH1 importin, and the E3 ubiquitin ligase COP1 indirectly protects HYL1 from degradation in a light-dependent manner. Furthermore, proper localization of HYL1 in Dicing bodies is regulated by MOS2. On the other hand, the Dicing body localization of DCL1 is regulated by NOT2b, which also interacts with SE in the nucleus. Post-translational modifications are substantial factors that contribute to protein functional diversity and provide a fine-tuning system for the regulation of protein activity. The phosphorylation status of HYL1 is crucial for its activity/stability and is a result of the interplay between kinases (MPK3 and SnRK2) and phosphatases (CPL1 and PP4). Additionally, MPK3 and SnRK2 are known to phosphorylate SE. Several other proteins (e.g., TGH, CDF2, SIC, and RCF3) that interact with Microprocessor have been found to influence its RNA-binding and processing activities. In this minireview, recent findings on the various modes of Microprocessor activity regulation are discussed.

The 'how' and 'where' of plant microRNAs

Contents 1002 I. 1002 II. 1007 III. 1010 IV. 1013 1013 References 1013 SUMMARY: MicroRNAs (miRNAs) are small non-coding RNAs, of typically 20-24 nt, that regulate gene expression post-transcriptionally through sequence complementarity. Since the identification of the first miRNA, lin-4, in the nematode Caenorhabditis elegans in 1993, thousands of miRNAs have been discovered in animals and plants, and their regulatory roles in numerous biological processes have been uncovered. In plants, research efforts have established the major molecular framework of miRNA biogenesis and modes of action, and are beginning to elucidate the mechanisms of miRNA degradation. Studies have implicated restricted and surprising subcellular locations in which miRNA biogenesis or activity takes place. In this article, we summarize the current knowledge on how plant miRNAs are made and degraded, and how they repress target gene expression. We discuss not only the players involved in these processes, but also the subcellular sites in which these processes are known or implicated to take place. We hope to raise awareness that the cell biology of miRNAs holds the key to a full understanding of these enigmatic molecules.

Translation of noncoding RNAs: Focus on lncRNAs, pri-miRNAs, and circRNAs

Mammalian genome is pervasively transcribed, producing large number of noncoding RNAs (ncRNAs), including long noncoding RNAs (lncRNAs), primary miRNAs (pri-miRNA), and circular RNAs (circRNAs). The translation of these ncRNAs has long been overlooked. Increasing studies, however, based on ribosome profiling in various organisms provide important clues to unanticipated translation potential of lncRNAs. Moreover, a few functional peptides encoded by lncRNAs and pri-miRNAs underline the significance of their translation. Recently, several novel researches also evidence the translation of endogenous circRNAs. Given the functional significance exemplified by peptides translated by some ncRNAs and their pervasive translation, it is not too far-fetched to image that abnormal translation of ncRNAs may contribute to human diseases. Through challenging, deciphering ncRNA translation is required for comprehensive understanding of biology and medicine. In this review, we firstly present evidence concerning translation potential of lncRNAs and go on to introduce a few functional short peptides encoded by lncRNAs. Then, salient observations showing translation of pri-miRNAs and circRNAs are described in detail. We end by discussing the impact of ncRNA translation beyond producing peptides and referring briefly to the potential role of abnormal ncRNA translation in human diseases.