Biology subjects

Le Masson, M.

Publications and source records attributed to Le Masson, M..

4 recordsLinked to original sources

bioRxiv2024

The dual trxG/PcG protein ULTRAPETALA1 modulates H3K27me3 and directly enhances POLYCOMB REPRESSIVE COMPLEX 2 activity for fine-tuned reproductive transitions

AbstractThe antagonistic POLYCOMB (PcG) REPRESSIVE COMPLEX 2 (PRC2) and trithorax (trxG) chromatin machineries play a major role in orchestrating gene expression during the development of multicellular eukaryotes. These complexes are well known for depositing and maintaining the repressive H3K27me3 and activating H3K4me3 marks, respectively. However, the mechanisms that govern the switch between these functions remains elusive, especially in plants, whose lifelong, flexible development relies heavily on this process. Here we demonstrate that the plant specific ULTRAPETALA1 (ULT1) protein, previously reported as a trxG factor that antagonizes the PRC2 enzymatic subunit CURLY LEAF (CLF), also exhibits a repressive function, increasing H3K27me3 levels at over a thousand genes. We discovered a physical interaction between ULT1 and PRC2 components, particularly the SWINGER (SWN) enzymatic subunit. We further show that in vitro ULT1 significantly enhances the enzymatic activity of PRC2SWN, and to a lesser extent also that of PRC2CLF, corroborating our epigenomic and developmental genetic data that reveal different ULT1 activity depending on the catalytic subunit of the PRC2 complex. This study provides new insights into the relative activities of CLF and SWN and introduces a novel mechanistic framework for a chromatin switch mediated by a bivalent trxG/PcG factor. Key messageULTRAPETALA1 counteracts or promotes PRC2 activity at hundreds of developmental genes in Arabidopsis thaliana, and activates the deposition of the repressive H3K27me3 chromatin mark via direct interaction with PRC2. This is the first instance of a bivalent factor which functions as a cofactor of PRC2 HMTs.

genetics↗

bioRxiv2024

Manipulating plant development by editing histone methylation with the dCas9 tool: the CUC3 boundary gene as a case study

Chromatin modifications are deemed to associate with gene expression patterns, yet their causal function on transcription and cell fate remains unestablished. Here, we demonstrate the direct impact of an epigenome editing tool designed to remove a key chromatin modification at a precise locus in living plants, with outcomes from the molecular to the developmental scale. The manipulated mark, H3K27me3, deposited at Lysine 27 of Histone 3 by the methyltransferase Polycomb PRC2 complex, is associated with the repression of developmental genes. As a new approach to investigate this histone mark genuine function, we used a dCas9-derived tool to bring a specific demethylase function at the CUP SHAPED COTYLEDON 3 (CUC3) organ frontier gene, aiming to remove the trimethyl mark at H3K27. We show that the removal of H3K27me3 at the locus causally induces activation of CUC3 expression within its regular territory, as well as ectopically. Our precise perturbation strategy reveals that alterations in a chromatin mark lead to changes in transcription and developmental gene expression patterning, with sharp consequences on plant morphogenesis and growth. Our work thus constitutes a proof of concept for the effective use of epigenome editing tools in unveiling the causal role of mark dynamics, supported by both molecular and developmental evidences.

plant biology↗

bioRxiv2021

The making of cauliflowers: the story of unsuccessful flowers

The arrangement of plant organs, called phyllotaxis, produce remarkable spiral or whorled patterns. Cauliflowers present a unique phyllotaxis with a multitude of spirals over a wide range of scales. How such a self-similar fractal organization emerges from developmental mechanisms has remained elusive. Combining experimental assays with modeling, we found that cauliflowers arise due to the hysteresis of the bistable floral network that generates inflorescences imprinted by a transient floral state. We further show how additional mutations affecting meristem growth dynamics can induce the production of conical phyllotactic structures reminiscent of the conspicuous fractal Romanesco shape. This study reveals how the spectacular morphological modification of the inflorescences in cauliflower and Romanesco shape arises from the hysteresis of the genetic programs controlling inflorescence development. One Sentence SummaryThe molecular making of cauliflowers

plant biology↗

bioRxiv2018

Control of stem-cell niche establishment in Arabidopsis flowers by REVOLUTA and the LEAFY-RAX1 module

Plants retain the ability to produce organs throughout their life by maintaining active stem cell niches called meristems. The shoot apical meristem (SAM) is responsible for the growth of aerial plant structures. In Arabidopsis thaliana, the SAM initially produces leaves during the vegetative phase and later flowers during reproductive development. In the early stages of floral initiation, a group of cells first emerges from the SAM to form a stereotypically organized meristematic structure on its flank. However, the molecular mechanisms underlying the acquisition of this specific meristematic organization remain elusive. We show here that the transcription factors LEAFY (LFY) and REVOLUTA (REV) control two partially redundant pathways controlling meristematic organization in early flower primordia. We found that LFY acts through the transcription factor REGULATOR OF AXILLARY MERISTEM1 (RAX1) and we provide mechanistic insights in how RAX1 allows meristem identity establishment in young flowers. Our work provides a molecular link between the processes of meristem formation and floral identity acquisition in the nascent flower.

plant biology↗