Biology subjects

Thieffry, A.

Publications and source records attributed to Thieffry, A..

5 recordsLinked to original sources

bioRxiv2024

Arabidopsis terminal nucleotidyl transferases govern secondary siRNA production at distinct steps

In plants, RNA interference (RNAi) mediated by the endonucleolytic RNA-Induced Silencing Complex (RISC) defends against foreign RNA and regulates endogenous genes. Targeting of RISC to foreign RNA establishes amplification loops, wherein RNA-dependent RNA Polymerase 6 (RDR6) synthesizes double-stranded RNA (dsRNA) for secondary small interfering RNA (siRNA) biogenesis, using cleavage fragments of RNA targeted by RISC programmed with a primary siRNA as template. Secondary siRNA production from endogenous RISC targets requires a particular primary small RNA size or target site multiplicity. siRNA amplification in yeast and nematodes requires terminal nucleotidyl transferases (TNTases), but their roles in plants are unclear. Here, we demonstrate two functions of TNTases in siRNA amplification in Arabidopsis thaliana. URT1 prevents initiation of microRNA-induced secondary siRNA formation through uridylation of 5-cleavage fragments, sometimes redundantly with the exosome and the TNTase HESO1. Once initiated via RDR6 recruitment, HESO1 and other TNTases stimulate secondary siRNA formation by producing 2-nt 3overhangs on RDR6-synthesized dsRNA to yield substrates for processing into siRNAs by DICER-LIKE4. These results define molecular mechanisms by which TNTases control siRNA amplification in plants.

plant biology↗

bioRxiv2021

Nuclear and cytoplasmic RNA exosomes and PELOTA1 prevent miRNA-induced secondary siRNA production in Arabidopsis

Amplification of short interfering RNA (siRNAs) via RNA dependent RNA Polymerases (RdRPs) is of fundamental importance in RNA silencing. In plants, silencing by microRNAs (miRNAs) generally does not lead to engagement of RdRPs, in part thanks to an as yet poorly understood activity of the cytoplasmic exosome adaptor SKI2. Here, we show that mutation of the cytoplasmic exosome subunit RRP45B results in siRNA production very similar to what is observed in ski2 mutants. Furthermore, loss of the nuclear exosome adaptor HEN2 leads to secondary siRNA production from miRNA targets largely distinct from those producing siRNAs in ski2. Importantly, mutation of the Release Factor paralogue PELOTA1 required for subunit dissociation of stalled ribosomes causes siRNA production from miRNA targets overlapping with, but distinct from, those affected in ski2 and rrp45b mutants. We also show that miRNA-induced illicit secondary siRNA production correlates with miRNA levels rather than accumulation of stable 5-cleavage fragments. We propose that stalled RNA-induced Silencing Complex (RISC) and ribosomes, but not stable target mRNA cleavage fragments released from RISC, trigger secondary siRNA production, and that the exosome limits siRNA amplification by reducing RISC dwell time on miRNA target mRNAs while PELOTA1 does so by reducing ribosome stalling.

molecular biology↗

bioRxiv2021

PAMP-triggered Genetic Reprogramming Involves Widespread Alternative Transcription Initiation and an Immediate Transcription Factor Wave

Immune responses triggered by pathogen-associated molecular patterns (PAMPs) are key to pathogen defense, but drivers of the genetic reprogramming required to reach the immune state remain incompletely understood in plants. Here, we report a time-course study of the establishment of PAMP-triggered immunity (PTI) using cap analysis of gene expression (CAGE). Our results show that as much as 15% of all PAMP response genes display alternative transcription initiation. In several cases, use of alternative TSSs may be regulatory as it determines inclusion of target peptides or protein domains, or occurrence of upstream open reading frames (uORFs) in mRNA leader sequences. We also find that 60% of PAMP-response genes respond much earlier than previously thought. In particular, a previously unnoticed cluster of rapidly and transiently PAMP-induced genes is enriched in transcription factors whose functions, previously associated with biological processes as diverse as abiotic stress adaptation and stem cell activity, appear to converge on growth restriction. Furthermore, some examples of known potentiators of PTI, in one case under direct MAP kinase control, support the notion that the rapidly induced transcription factors could constitute direct links to PTI signaling pathways and drive gene expression changes underlying establishment of the immune state.

plant biology↗

bioRxiv2018

CAGEfightR: Cap Analysis of Gene Expression (CAGE) in R/Bioconductor

We developed the CAGEfightR R/Biconductor-package for analyzing CAGE data. CAGEfightR allows for fast and memory efficient identification of transcription start sites (TSSs) and predicted enhancers. Downstream analysis, including annotation, quantification, visualization and TSS shape statistics are implemented in easy-to-use functions. The package is freely available at https://bioconductor.org/packages/CAGEfightR

bioinformatics↗

bioRxiv2018

Comprehensive profiling of the fission yeast transcription start site activity during stress and media response

Fission yeast, Schizosaccharomyces pombe, is an attractive model organism for transcriptional and chromatin biology research. Such research is contingent on accurate annotation of transcription start sites (TSSs). However, comprehensive genome-wide maps of TSSs and their usage across commonly applied laboratory conditions and treatments for S. pombe are lacking. To this end, we profiled TSS activity genome-wide in S. pombe cultures exposed to heat shock, nitrogen starvation, hydrogen peroxide and two commonly applied media, YES and EMM2, using Cap Analysis of Gene Expression (CAGE). CAGE-based annotation of TSSs is substantially more accurate than existing PomBase annotation; on average, CAGE TSSs fall 50-75 bp downstream of PomBase TSSs and co-localize with nucleosome boundaries. In contrast to higher eukaryotes, S. pombe does not show sharp and dispersed TSS distributions. Our data recapitulate known S. pombe stress expression response patterns and identify stress- and mediaresponsive alternative TSSs. Notably, alteration of growth medium induces changes of similar magnitude as some stressors. We show a link between nucleosome occupancy and genetic variation, and that the proximal promoter region is genetically diverse between S. pombe strains. Our detailed TSS map constitute a central resource for S. pombe gene regulation research.

genomics↗