Unequal genetic redundancy between the PcG proteins CLF and SWN has created distinct biochemical properties

Individual cells of multicellular organisms display distinct usage of identical genetic information. Gene expression states often correlate with posttranslational modifications (PTMs) on histones. Methylation of histone H3 on its lysine residue in position 27 (H3K27me) is such a signature epigenetic mark and its trimethylated form, H3K27me3, strongly correlates with transcriptional repression. In the model plant Arabidopsis thaliana (Arabidopsis), H3K27me3 in the sporophyte is exclusively catalyzed by the highly conserved histone methyltransferases CURLY LEAF (CLF) and SWINGER (SWN), which act in a protein complex called Polycomb repressive complex 2 (PRC2). Arabidopsis swn mutant plants do not have an obvious morphological phenotype, while clf mutant plants have a mild phenotype compared to the clf swn double mutant plants, which are full knockouts of sporophytic H3K27me3. However, a comparative biochemical analysis of CLF and SWN proteins in a PRC2 context has been lacking until now and it was uncertain if distinct differences are encoded in the coding or non-coding parts of CLF and SWN genes. This work shows that CLF and SWN share the enzymatic activity in a PRC2 oligomeric context to catalyze H3K27 methylation, but that their contribution to H3K27me3 is unequal due to an individually different specificity (Km/kcat) to H3K27 methylated forms (H3K27me0/1/2). Given their overlapping expression in meristems and their interchangeability of the respective non-coding parts, however, CLF and SWN are genetically redundant in planta. These findings are consistent with previous H3K27me3 ChIP-seq data in clf and swn mutants and strengthen the argument, that CLF protein is able to hypermethylate its target genes, classified as CLF-dependent genes, in the absence of SWN protein; as is the case in the swn mutant. Conversely, SWN protein relies on the presence of CLF protein to achieve H3K27me3 at these CLF-dependent target genes; as is the case in the clf mutant. My results demonstrate how the duplication of the common ancestral gene of CLF and SWN at the base of Angiosperm phylogeny has led to an unequal genetic redundancy in Arabidopsis. The results further imply a strong divergence of the coding sequences of Arabidopsis CLF and SWN from their green-lineage orthologues outside the core Brassicaceae. I anticipate my study to be a starting point to gain a better understanding of the PRC2 oligomeric composition in Arabidopsis and to further characterize such PRC2 variants

NLR immune receptors: Structure and function in plant disease resistance

Nucleotide-binding and leucine-rich repeat receptors (NLRs) are a diverse family of intracellular immune receptors that play crucial roles in recognizing and responding to pathogen invasion in plants. This review discusses the overall model of NLR activation and provides an in-depth analysis of the different NLR domains, including N-terminal executioner domains, the nucleotide-binding oligomerization domain (NOD) module, and the leucine-rich repeat (LRR) domain. Understanding the structure-function relationship of these domains is essential for developing effective strategies to improve plant disease resistance and agricultural productivity

Bacteria may induce the secretion of mucin-like proteins by the diatom phaeodactylum tricornutum

Benthic diatoms live in photoautotrophic/heterotrophic biofilm communities embedded in a matrix of secreted extracellular polymeric substances. Closely associated bacteria influence their growth, aggregation, and secretion of exopolymers. We have studied a diatom/bacteria model community, in which a marine Roseobacter strain is able to grow with secreted diatom exopolymers as sole source of carbon. The strain influences the aggregation of Phaeodactylum tricornutum by inducing a morphotypic transition from planktonic, fusiform cells to benthic, oval cells. Analysis of the extracellular soluble proteome of P. tricornutum in the presence and absence of bacteria revealed constitutively expressed newly identified proteins with mucin-like domains that appear to be typical for extracellular diatom proteins. In contrast to mucins, the proline-, serine-, threonine-rich (PST) domains in these proteins were also found in combination with protease-, glucosidase and leucine-rich repeat (LRR-) domains. Bioinformatic functional predictions indicate that several of these newly identified diatom-specific proteins may be involved in algal defense, intercellular signaling, and aggregation This article is protected by copyright. All rights reserved.publishe