The MYB33, MYB65, and MYB101 transcription factors affect Arabidopsis and potato responses to drought by regulating the ABA signaling pathway.

Drought is one of the main climate threats limiting crop production. Potato is one of the four most important food crop species worldwide and is sensitive to water shortage. The CBP80 gene was shown to affect Arabidopsis and potato responses to drought by regulating the level of microRNA159 and, consequently, the levels of the MYB33 and MYB101 transcription factors (TFs). Here, we show that three MYB TFs, MYB33, MYB65, and MYB101, are involved in plant responses to water shortage. Their downregulation in Arabidopsis causes stomatal hyposensitivity to abscisic acid (ABA), leading to reduced tolerance to drought. Transgenic Arabidopsis and potato plants overexpressing these genes, with a mutated recognition site in miR159, show hypersensitivity to ABA and relatively high tolerance to drought conditions. Thus, the MYB33, MYB65, and MYB101 genes may be potential targets for innovative breeding to obtain crops with relatively high tolerance to drought.

tRex: A Web Portal for Exploration of tRNA-Derived Fragments in Arabidopsis thaliana.

tRNA-derived fragments (tRFs) constitute a new class of short regulatory RNAs that are a product of nascent or mature tRNA processing. tRF sequences have been identified in all domains of life; however, most published research pertains to human, yeast and some bacterial organisms. Despite growing interest in plant tRFs and accumulating evidence of their function in plant development and stress responses, no public, web-based repository dedicated to these molecules is currently available. Here, we introduce tRex (http://combio.pl/trex)-the first comprehensive data-driven online resource specifically dedicated to tRFs in the model plant Arabidopsis thaliana. The portal is based on verified Arabidopsis tRNA annotation and includes in-house-generated and publicly available small RNA sequencing experiments from various tissues, ecotypes, genotypes and stress conditions. The provided web-based tools are designed in a user-friendly manner and allow for seamless exploration of the data that are presented in the form of dynamic tables and cumulative coverage profiles. The tRex database is connected to external genomic and citation resources, which makes it a one-stop solution for Arabidopsis tRF-related research.

A stable tRNA-like molecule is generated from the long noncoding RNA GUT15 in Arabidopsis.

The Arabidopsis GUT15 RNA belongs to a class of noncoding RNAs that are expressed from the intergenic regions of protein-coding genes. We show that the RNA polymerase II transcribed GUT15 transcript serves as a precursor for two stable RNA species, a tRNA-like molecule and GUT15-tRF-F5, which are both encoded by the final intron in the GUT15 gene. The GUT15-encoded tRNA-like molecule cannot be autonomously transcribed by RNA polymerase III. However, this molecule contains a CCA motif, suggesting that it may enter the tRNA maturation pathway. The GUT15-encoded tRNA-like sequence has an inhibiting effect on the splicing of its host intron. Moreover, we demonstrate that the canonical tRNA genes nested within introns do not affect the splicing patterns of their host protein-coding transcripts.

Promoter-based identification of novel non-coding RNAs reveals the presence of dicistronic snoRNA-miRNA genes in Arabidopsis thaliana.

BACKGROUND: In the past few decades, non-coding RNAs (ncRNAs) have emerged as important regulators of gene expression in eukaryotes. Most studies of ncRNAs in plants have focused on the identification of silencing microRNAs (miRNAs) and small interfering RNAs (siRNAs). Another important family of ncRNAs that has been well characterized in plants is the small nucleolar RNAs (snoRNAs) and the related small Cajal body-specific RNAs (scaRNAs). Both target chemical modifications of ribosomal RNAs (rRNAs) and small nuclear RNAs (snRNAs). In plants, the snoRNA genes are organized in clusters, transcribed by RNA Pol II from a common promoter and subsequently processed into mature molecules. The promoter regions of snoRNA polycistronic genes in plants are highly enriched in two conserved cis-regulatory elements (CREs), Telo-box and Site II, which coordinate the expression of snoRNAs and ribosomal protein coding genes throughout the cell cycle. RESULTS: In order to identify novel ncRNA genes, we have used the snoRNA Telo-box/Site II motifs combination as a functional promoter indicator to screen the Arabidopsis genome. The predictions generated by this process were tested by detailed exploration of available RNA-Seq and expression data sets and experimental validation. As a result, we have identified several snoRNAs, scaRNAs and 'orphan' snoRNAs. We also show evidence for 16 novel ncRNAs that lack similarity to any reported RNA family. Finally, we have identified two dicistronic genes encoding precursors that are processed to mature snoRNA and miRNA molecules. We discuss the evolutionary consequences of this result in the context of a tight link between snoRNAs and miRNAs in eukaryotes. CONCLUSIONS: We present an alternative computational approach for non-coding RNA detection. Instead of depending on sequence or structure similarity in the whole genome screenings, we have explored the properties of promoter regions of well-characterized ncRNAs. Interestingly, besides expected ncRNAs predictions we were also able to recover single precursor arrangement for snoRNA-miRNA. Accompanied by analyses performed on rice sequences, we conclude that such arrangement might have interesting functional and evolutionary consequences and discuss this result in the context of a tight link between snoRNAs and miRNAs in eukaryotes.

The liverwort Pellia endiviifolia shares microtranscriptomic traits that are common to green algae and land plants.

Liverworts are the most basal group of extant land plants. Nonetheless, the molecular biology of liverworts is poorly understood. Gene expression has been studied in only one species, Marchantia polymorpha. In particular, no microRNA (miRNA) sequences from liverworts have been reported. Here, Illumina-based next-generation sequencing was employed to identify small RNAs, and analyze the transcriptome and the degradome of Pellia endiviifolia. Three hundred and eleven conserved miRNA plant families were identified, and 42 new liverwort-specific miRNAs were discovered. The RNA degradome analysis revealed that target mRNAs of only three miRNAs (miR160, miR166, and miR408) have been conserved between liverworts and other land plants. New targets were identified for the remaining conserved miRNAs. Moreover, the analysis of the degradome permitted the identification of targets for 13 novel liverwort-specific miRNAs. Interestingly, three of the liverwort microRNAs show high similarity to previously reported miRNAs from Chlamydomonas reinhardtii. This is the first observation of miRNAs that exist both in a representative alga and in the liverwort P. endiviifolia but are not present in land plants. The results of the analysis of the P. endivifolia microtranscriptome support the conclusions of previous studies that placed liverworts at the root of the land plant evolutionary tree of life.

FUS regulates a subset of snoRNA expression and modulates the level of rRNA modifications.

FUS is a multifunctional protein involved in many aspects of RNA metabolism, including transcription, splicing, translation, miRNA processing, and replication-dependent histone gene expression. In this work, we show that FUS depletion results in the differential expression of numerous small nucleolar RNAs (snoRNAs) that guide 2'-O methylation (2'-O-Me) and pseudouridylation of specific positions in ribosomal RNAs (rRNAs) and small nuclear RNAs (snRNAs). Using RiboMeth-seq and HydraPsiSeq for the profiling of 2'-O-Me and pseudouridylation status of rRNA species, we demonstrated considerable hypermodification at several sites in HEK293T and SH-SY5Y cells with FUS knockout (FUS KO) compared to wild-type cells. We observed a similar direction of changes in rRNA modification in differentiated SH-SY5Y cells with the FUS mutation (R495X) related to the severe disease phenotype of amyotrophic lateral sclerosis (ALS). Furthermore, the pattern of modification of some rRNA positions was correlated with the abundance of corresponding guide snoRNAs in FUS KO and FUS R495X cells. Our findings reveal a new role for FUS in modulating the modification pattern of rRNA molecules, that in turn might generate ribosome heterogeneity and constitute a fine-tuning mechanism for translation efficiency/fidelity. Therefore, we suggest that increased levels of 2'-O-Me and pseudouridylation at particular positions in rRNAs from cells with the ALS-linked FUS mutation may represent a possible new translation-related mechanism that underlies disease development and progression.

Long Intergenic Noncoding RNAs Affect Biological Pathways Underlying Autoimmune and Neurodegenerative Disorders.

Long intergenic noncoding RNAs (lincRNAs) are a class of independently transcribed molecules longer than 200 nucleotides that do not overlap known protein-coding genes. LincRNAs have diverse roles in gene expression and participate in a spectrum of biological processes. Dysregulation of lincRNA expression can abrogate cellular homeostasis, cell differentiation, and development and can also deregulate the immune and nervous systems. A growing body of literature indicates their important and multifaceted roles in the pathogenesis of several different diseases. Furthermore, certain lincRNAs can be considered potential therapeutic targets and valuable diagnostic or prognostic biomarkers capable of predicting the onset of a disease, its degree of activity, or the progression phase. In this review, we discuss possible mechanisms and molecular functions of lincRNAs in the pathogenesis of selected autoimmune and neurodegenerative disorders: multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's syndrome, Huntington's disease, Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis. This summary can provide new ideas for future research, diagnosis, and treatment of these highly prevalent and devastating diseases.

The Novel Role of hnRNP UL1 in Human Cell Nucleoli.

hnRNP UL1 plays an important role in cell nuclei, where it is recruited to DNA damage sites and is involved in the repair of DNA double-strand breaks. Furthermore, this protein is known as a transcriptional repressor of RNA polymerase II genes. In the present study, we have shown that hnRNP UL1 is also localized in the nucleoli of human cells. Upon investigating its function, we found that hnRNP UL1 stimulates ribosomal DNA (rDNA) gene transcription. Moreover, we observed that cells with hnRNP UL1 silencing exhibited increased sensitivity to DNA damage. We also showed that hnRNP UL1 interacts with γH2A.X, RPA32, XRCC1, and Chk1 in cell nucleoli, suggesting its involvement in the repair of rDNA damage.

Arabidopsis microRNA expression regulation in a wide range of abiotic stress responses.

Arabidopsis microRNA expression regulation was studied in a wide array of abiotic stresses such as drought, heat, salinity, copper excess/deficiency, cadmium excess, and sulfur deficiency. A home-built RT-qPCR mirEX platform for the amplification of 289 Arabidopsis microRNA transcripts was used to study their response to abiotic stresses. Small RNA sequencing, Northern hybridization, and TaqMan® microRNA assays were performed to study the abundance of mature microRNAs. A broad response on the level of primary miRNAs (pri-miRNAs) was observed. However, stress response at the level of mature microRNAs was rather confined. The data presented show that in most instances, the level of a particular mature miRNA could not be predicted based on the level of its pri-miRNA. This points to an essential role of posttranscriptional regulation of microRNA expression. New Arabidopsis microRNAs responsive to abiotic stresses were discovered. Four microRNAs: miR319a/b, miR319b.2, and miR400 have been found to be responsive to several abiotic stresses and thus can be regarded as general stress-responsive microRNA species.