Biology subjects

Maple, R.

Publications and source records attributed to Maple, R..

5 recordsLinked to original sources

bioRxiv2025

Co-transcriptional splicing changes combine with reduced productive transcription initiation for cold-induced repression of FLC

The Arabidopsis floral repressor locus FLC is epigenetically silenced during winter cold to align flowering with spring. During weeks of cold exposure, FLC transcription is progressively reduced both by transcriptional repression mediated by FLC antisense transcription, and epigenetic silencing implemented through a Polycomb-mediated epigenetic switch. In the warm, FLC is transcriptionally repressed by coordinated changes in transcription initiation and RNA PolII speed in a mechanism involving proximal termination. Whether similar mechanisms contribute to the cold-induced FLC transcriptional repression is unknown. Here, we combine mathematical modelling and transcription profiling to investigate FLC transcriptional changes during the cold. We find different dynamics of spliced and unspliced transcripts during cold exposure with only a small change in PolII speed. We also show that, unlike short-term cold, long-term cold temperatures drive an increase in splicing rates while simultaneously reducing productive transcription at FLC. This process is influenced by antisense COOLAIR transcription but does not rely on proximal COOLAIR termination. Cold-induced transcriptional repression of FLC thus involves a decoupling of changes in productive transcription initiation from PolII speed and rates of co-transcriptional splicing, a different mechanism to that repressing FLC in the warm.

molecular biology↗

bioRxiv2024

Modular structure of RNA 3' processing condensates involving the Arabidopsis RNA binding protein FCA

Our understanding of the functional requirements underpinning biomolecular condensation in vivo is still relatively poor. The Arabidopsis RNA binding protein FCA is found in liquid-like nuclear condensates that function in transcription termination, promoting proximal polyadenylation at many targets in the Arabidopsis genome. To further understand the properties of these condensates in vivo we used single particle tracking experiments on FCA reporters stably expressed at endogenous levels in plant nuclei. These revealed FCA forms a core oligomer of [~]4 molecules that multimerizes into higher-order particles. This assembles into macromolecular condensates through the function of the coiled-coil protein FLL2, which is genetically required for FCA function. FLL2 predominately co-localizes with FCA in larger sized condensates. A missense mutation in the FCA RRM domain, also genetically required for FCA function, reduced both average FCA particle and condensate size but did not perturb the core oligomer. Our work points to a modular structure for FCA condensates involving multimerization of core oligomers that assemble into functional macromolecular condensates via associated RNA and FLL2 interactions.

molecular biology↗

bioRxiv2023

Proximal termination generates a transcriptional state that determines the rate of establishment of Polycomb silencing

Chromatin-mediated transcriptional silencing by Polycomb Repressive Complex 2 (PRC2) is critical for gene regulation in development and environmental responses. However, the mechanism and timescales controlling de novo establishment of PRC2 silencing are unclear. Here, we investigate PRC2 silencing at Arabidopsis FLOWERING LOCUS C (FLC), known to involve co-transcriptional RNA processing, histone demethylation activity, and PRC2 function; but so far not mechanistically connected. We develop and then test a computational model that describes how proximal polyadenylation/termination mediated by the RNA binding protein FCA induces H3K4me1 removal by the histone demethylase FLD. H3K4me1 removal feeds back to reduce RNA Pol II processivity and thus enhance early termination, thereby repressing productive transcription. The model predicts that this transcription-coupled repression controls the level of transcriptional antagonism to Polycomb action, Thus, the effectiveness of this repression dictates the timescale for establishment of Polycomb H3K27me3 silencing. Experimental validation of these model predictions allowed us to mechanistically connect co-transcriptional processing to setting the level of productive transcription at the locus, which then determines the rate of the ON to OFF switch to PRC2 silencing.

molecular biology↗

bioRxiv2023

The CPSF phosphatase module links transcription termination to chromatin silencing

The interconnections between co-transcriptional regulation, chromatin environment and transcriptional output remain poorly understood. Here, we investigate the mechanism underlying RNA 3 processing-mediated Polycomb silencing of Arabidopsis FLOWERING LOCUS C (FLC). We show a requirement for APRF1, a homologue of yeast Swd2 and human WDR82, known to regulate RNA Pol II during transcription termination. APRF1 interacts with TOPP4 (yeast Glc7/human PP1) and LD, the latter showing structural features found in Ref2/PNUTS; all components of the yeast and human phosphatase module of the CPF 3end processing machinery. LD has been shown to co-associate in vivo with the histone H3 K4 demethylase FLD. We show APRF1 and LD couple CPF-mediated cleavage and polyadenylation with removal of H3K4 monomethylation in the body of FLC, and this influences subsequent transcription. This work shows how transcription termination can change the local chromatin environment to modulate transcription of Arabidopsis FLC and affect flowering time.

molecular biology↗

bioRxiv2020

A transposon surveillance mechanism that safeguards plant male fertility during stress

Although plants are able to withstand a range of environmental conditions, spikes in ambient temperature can impact plant fertility causing reductions in seed yield and significant economic losses1,2. Therefore, understanding the precise molecular mechanisms that underpin plant fertility under environmental constraints is critical to safeguard future food production3. Here, we identified two Argonaute-like proteins whose activities are required to sustain male fertility in maize plants under high temperatures. We found that MALE-ASSOCIATED ARGONAUTE 1 and 2 (MAGO1 and MAGO2) associate with temperature-induced phased secondary small RNAs in pre-meiotic anthers and are essential to control the activity of retrotransposons in male meiocyte initials. Biochemical and structural analyses revealed how MAGO2 activity and its interaction with retrotransposon RNA targets are modulated through the dynamic phosphorylation of a set of highly conserved surface-located serine residues. Our results demonstrate that an Argonaute-dependent RNA-guided surveillance mechanism is critical in plants to sustain male fertility under environmentally constrained conditions by controlling the mutagenic activity of transposons in male germ cells.

plant biology↗