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Specific recognition of N6-methyladenosine (m6A) in mRNA by RNA-binding proteins containing a YT521-B homology (YTH) domain is important in eukaryotic gene regulation. The Arabidopsis YTH domain protein ECT2 is thought to bind to mRNA at URU(m6A)Y sites, yet RR(m6A)CH is the canonical m6A consensus site in all eukaryotes and ECT2 functions require m6A-binding activity. Here, we apply iCLIP (individual nucleotide resolution crosslinking and immunoprecipitation) and HyperTRIBE (targets of RNA-binding proteins identified by editing) to define high-quality target sets of ECT2 and analyze the patterns of enriched sequence motifs around ECT2 crosslink sites. Our analyses show that ECT2 does in fact bind to RR(m6A)CH. Pyrimidine-rich motifs are enriched around, but not at m6A sites, reflecting a preference for N6-adenosine methylation of RRACH/GGAU islands in pyrimidine-rich regions. Such motifs, particularly oligo-U and UNUNU upstream of m6A sites, are also implicated in ECT2 binding via its intrinsically disordered region (IDR). Finally, URUAY-type motifs are enriched at ECT2 crosslink sites, but their distinct properties suggest function as sites of competition between binding of ECT2 and as yet unidentified RNA-binding proteins. Our study provides coherence between genetic and molecular studies of m6A-YTH function in plants and reveals new insight into the mode of RNA recognition by YTH domain-containing proteins., eLife digest Genes are strings of genetic code that contain instructions for producing a cell’s proteins. Active genes are copied from DNA into molecules called mRNAs, and mRNA molecules are subsequently translated to create new proteins. However, the number of proteins produced by a cell is not only limited by the number of mRNA molecules produced by copying DNA. Cells use a variety of methods to control the stability of mRNA molecules and their translation efficiency to regulate protein production. One of these methods involves adding a chemical tag, a methyl group, onto mRNA while it is being created. These methyl tags can then be used as docking stations by RNA-binding proteins that help regulate protein translation. Most eukaryotic species – which include animals, plants and fungi – use the same system to add methyl tags to mRNA molecules. One methyl tag in particular, known as m6A, is a well-characterised docking site for a particular type of RNA-binding protein that goes by the name of ECT2 in plants. However, in the flowering plant Arabidopsis thaliana, ECT2 was thought to bind to an mRNA sequence different from the one normally carrying the chemical tag, creating obvious confusion about how the system works in plants. Arribas-Hernández, Rennie et al. investigated this question using advanced large-scale biochemical techniques, and discovered that conventional m6A methyl tags are indeed used by ECT2 in Arabidopsis thaliana. The confusion likely arose because the sequence ECT2 was thought bind is often located in close proximity to the m6A tags, possibly acting as docking stations for proteins that can influence the ability of ECT2 to bind mRNA. Arribas-Hernández, Rennie et al. also uncovered additional mRNA sequences that directly interact with parts of ECT2 previously unknown to participate in mRNA binding. These findings provide new insights into how chemical labels in mRNA control gene activity. They have broad implications that extend beyond plants into other eukaryotic species, including humans. Since this chemical labelling system has a major role in controlling plant growth, these findings could be leveraged in biotechnology applications to improve crop yields and enhance plant-based food production.

BackgroundRNA-binding proteins interact with their target RNAs at specific sites. These binding sites can be determined genome-wide through individual nucleotide resolution crosslinking immunoprecipitation (iCLIP). Subsequently, the binding sites have to be visualized. So far, no visualization tool exists that is easily accessible but also supports restricted access so that data can be shared among collaborators.ResultsHere we present SEQing, a customizable interactive dashboard to visualize crosslink sites on target genes of RNA-binding proteins that have been obtained by iCLIP. Moreover, SEQing supports RNA-seq data that can be displayed in a diffrerent window tab. This allows, e.g. crossreferencing the iCLIP data with genes differentially expressed in mutants of the RBP and thus obtain some insights into a potential functional relevance of the binding sites. Additionally, detailed information on the target genes can be incorporated in another tab.ConclusionSEQing is written in Python3 and runs on Linux. The web-based access makes iCLIP data easily accessible, even with mobile devices. SEQing is customizable in many ways and has also the option to be secured by a password. The source code is available at https://github.com/malewins/SEQing.

Background Functions for RNA-binding proteins in orchestrating plant development and environmental responses are well established. However, the lack of a genome-wide view of their in vivo binding targets and binding landscapes represents a gap in understanding the mode of action of plant RNA-binding proteins. Here, we adapt individual nucleotide resolution crosslinking and immunoprecipitation (iCLIP) genome-wide to determine the binding repertoire of the circadian clock-regulated Arabidopsis thaliana glycine-rich RNA-binding protein AtGRP7. Results iCLIP identifies 858 transcripts with significantly enriched crosslink sites in plants expressing AtGRP7-GFP that are absent in plants expressing an RNA-binding-dead AtGRP7 variant or GFP alone. To independently validate the targets, we performed RNA immunoprecipitation (RIP)-sequencing of AtGRP7-GFP plants subjected to formaldehyde fixation. Of the iCLIP targets, 452 were also identified by RIP-seq and represent a set of high-confidence binders. AtGRP7 can bind to all transcript regions, with a preference for 3′ untranslated regions. In the vicinity of crosslink sites, U/C-rich motifs are overrepresented. Cross-referencing the targets against transcriptome changes in AtGRP7 loss-of-function mutants or AtGRP7-overexpressing plants reveals a predominantly negative effect of AtGRP7 on its targets. In particular, elevated AtGRP7 levels lead to damping of circadian oscillations of transcripts, including DORMANCY/AUXIN ASSOCIATED FAMILY PROTEIN2 and CCR-LIKE. Furthermore, several targets show changes in alternative splicing or polyadenylation in response to altered AtGRP7 levels. Conclusions We have established iCLIP for plants to identify target transcripts of the RNA-binding protein AtGRP7. This paves the way to investigate the dynamics of posttranscriptional networks in response to exogenous and endogenous cues. Electronic supplementary material The online version of this article (doi:10.1186/s13059-017-1332-x) contains supplementary material, which is available to authorized users.

This study focused on the identification and phylogenetic analysis of glycine-rich RNA binding proteins that contain an RNA recognition motif (RRM)-type RNA binding domain in addition to a region with contiguous glycine residues in representative plant species. In higher plants, glycine-rich proteins with an RRM have met considerable interest as they are responsive to environmental cues and play a role in cold tolerance, pathogen defense, flowering time control, and circadian timekeeping. To identify such RRM containing proteins in plant genomes we developed an RRM profile based on the known glycine-rich RRM containing proteins in the reference plant Arabidopsis thaliana. The application of this remodeled RRM profile that omitted sequences from non-plant species reduced the noise when searching plant genomes for RRM proteins compared to a search performed with the known RRM_1 profile. Furthermore, we developed an island scoring function to identify regions with contiguous glycine residues, using a sliding window approach. This approach tags regions in a protein sequence with a high content of the same amino acid, and repetitive structures score higher. This definition of repetitive structures in a fixed sequence length provided a new glance for characterizing patterns which cannot be easily described as regular expressions. By combining the profile-based domain search for well-conserved regions (the RRM) with a scoring technique for regions with repetitive residues we identified groups of proteins related to the A. thaliana glycine-rich RNA binding proteins in eight plant species.

Arabidopsis thaliana glycine-rich RNA binding protein 7 (AtGRP7) is part of a negative feedback loop through which it regulates alternative splicing and steady-state abundance of its pre-mRNA. Here we use fluorescence correlation spectroscopy to investigate the requirements for AtGRP7 binding to its intron using fluorescently-labelled synthetic oligonucleotides. By systematically introducing point mutations we identify three nucleotides that lead to an increased K-d value when mutated and thus are critical for AtGRP7 binding. Simultaneous mutation of all three residues abrogates binding. The paralogue AtGRP8 binds to an overlapping motif but with a different sequence preference, in line with overlapping but not identical functions of this protein pair. Truncation of the glycine-rich domain reduces the binding affinity of AtGRP7, showing for the first time that the glycine-rich stretch of a plant hnRNP-like protein contributes to binding. Mutation of the conserved R-49 that is crucial for AtGRP7 function in pathogen defence and splicing abolishes binding. (C) 2014 Elsevier Inc. All rights reserved.

Background: In angiosperms, RNA-binding proteins with an RNA recognition motif (RRM)-type RNA interaction domain play an important role in developmental and environmental responses. Despite their pivotal role, a comprehensive analysis of their number and diversity has only been performed in Arabidopsis so far. Results: Here we present a detailed phylogenetic analysis of RRM-containing proteins in plants, the red algae Cyanidioschyzon merolae and cyanobacteria. We identified two major events during the diversification of the RRM in plants, one at the emergence of green plants, and the other at the water-to-land transition. We focused on proteins that combine a single RRM with a glycine-rich stretch, known as glycine-rich RNA-binding proteins (GRPs). We found that GRPs are present in cyanobacteria, however plant and cyanobacterial GRPs are not of monophyletic origin. We provide evidence that plant GRPs form a polyphyletic group.*Conclusion:*Our work provides insights into the origin of GRPs in plants. We determined that the RRM from plants and cyanobacteria do not have a common origin. We could also determine that the acquisition of the glycine-rich stretch has happened at least on three separate occasions during the evolution of GRPs. One event led to the emergence of cyanobacterial GRPs, while later acquisition events led to the emergence of GRPs in the green lineage. No GRPs were found in red or marine green algae. We found a subgroup of GRPs exclusive to land plants, and its appearance may be linked to challenges related to the water-to-land transition.