Reinforcement of transcriptional silencing by a positive feedback between DNA methylation and non-coding transcription

Loops, crosstalk, and compartmentalization: it takes many layers to regulate DNA methylation

DNA methylation is a conserved epigenetic modification associated with transposon silencing and gene regulation. The stability of this modification relies on intimate connections between DNA and histone modifications that generate self-reinforcing loops wherein the presence of one mark promotes the other. However, it is becoming increasingly clear that the efficiency of these loops is affected by cross-talk between pathways and by chromatin accessibility, which is heavily influenced by histone variants. Focusing primarily on plants, this review provides an update on the aforementioned self-reinforcing loops, highlights recent advances in understanding how DNA methylation pathways are restricted to prevent encroachment on genes, and discusses the roles of histone variants in compartmentalizing epigenetic pathways within the genome. This multilayered approach facilitates two essential, yet opposing functions, the ability to maintain heritable DNA methylation patterns while retaining the flexibility to modify these patterns during development.

LncRNAs exert indispensable roles in orchestrating the interaction among diverse noncoding RNAs and enrich the regulatory network of plant growth and its adaptive environmental stress response

With the advent of advanced sequencing technologies, non-coding RNAs (ncRNAs) are increasingly pivotal and play highly regulated roles in the modulation of diverse aspects of plant growth and stress response. This includes a spectrum of ncRNA classes, ranging from small RNAs to long non-coding RNAs (lncRNAs). Notably, among these, lncRNAs emerge as significant and intricate components within the broader ncRNA regulatory networks. Here, we categorize ncRNAs based on their length and structure into small RNAs, medium-sized ncRNAs, lncRNAs, and circle RNAs. Furthermore, the review delves into the detailed biosynthesis and origin of these ncRNAs. Subsequently, we emphasize the diverse regulatory mechanisms employed by lncRNAs that are located at various gene regions of coding genes, embodying promoters, 5'UTRs, introns, exons, and 3'UTR regions. Furthermore, we elucidate these regulatory modes through one or two concrete examples. Besides, lncRNAs have emerged as novel central components that participate in phase separation processes. Moreover, we illustrate the coordinated regulatory mechanisms among lncRNAs, miRNAs, and siRNAs with a particular emphasis on the central role of lncRNAs in serving as sponges, precursors, spliceosome, stabilization, scaffolds, or interaction factors to bridge interactions with other ncRNAs. The review also sheds light on the intriguing possibility that some ncRNAs may encode functional micropeptides. Therefore, the review underscores the emergent roles of ncRNAs as potent regulatory factors that significantly enrich the regulatory network governing plant growth, development, and responses to environmental stimuli. There are yet-to-be-discovered roles of ncRNAs waiting for us to explore.