DECREASE IN DNA METHYLATION 1-mediated epigenetic regulation maintains gene expression balance required for heterosis in Arabidopsis thaliana
Authors: Matsuo, K., Wu, R., Yonechi, H., Murakami, T., Takahashi, S., Kamio, A., Akter, M. A., Kamiya, Y., Nishimura, K., Matsuura, T., Tonosaki, K., Shimizu, M., Ikeda, Y., Kobayashi, H., Seki, M., Dennis, E. S., Fujimoto, R.
The study demonstrates that the chromatin remodeler DDM1 is essential for biomass heterosis in Arabidopsis thaliana hybrids, as loss of DDM1 function leads to reduced rosette growth and extensive genotype‑specific transcriptomic and DNA methylation changes. Whole‑genome bisulfite sequencing revealed widespread hypomethylation in ddm1 mutants, while salicylic acid levels were found unrelated to heterosis, indicating that epigenetic divergence, rather than SA signaling, underpins hybrid vigor.
The study used CRISPR/Cas9 to generate rice snrk1 mutants and performed integrated phenotypic, transcriptomic, proteomic, and phosphoproteomic analyses under normal and starvation conditions, revealing SnRK1’s dual role in promoting growth and mediating stress responses. Findings indicate sub-functionalization of SnRK1 subunits and identify novel phosphorylation targets linked to membrane trafficking, ethylene signaling, and ion transport.
The study adapted high‑throughput transposable‑element sequencing and introduced the deNOVOEnrich pipeline to map somatic TE insertions in Arabidopsis thaliana, uncovering ~200,000 new events across wild‑type and epigenetic mutant lines. Somatic integration is non‑random and TE‑specific, with families like ONSEN, EVADE, and AtCOPIA21 preferentially targeting chromosomal arms, genic regions, and chromatin marked by H2A.Z, H3K27me3, and H3K4me1, especially near environmentally‑responsive genes such as resistance loci and biosynthetic clusters.
The study reveals that the plant immune regulator NPR1 is modulated by opposing post‑translational modifications mediated by the nutrient‑sensing kinases TOR and SnRK1. Under normal conditions TOR phosphorylates NPR1 at Ser‑55/59 to suppress its activity, while salicylic‑acid‑induced SnRK1 activation inhibits TOR and phosphorylates NPR1 at Ser‑557, thereby activating NPR1 and linking metabolic status to immune signaling.
The study shows that the SnRK1 catalytic subunit KIN10 directs tissue-specific growth‑defense programs in Arabidopsis thaliana by reshaping transcriptomes. kin10 knockout mutants exhibit altered root transcription, reduced root growth, and weakened defense against Pseudomonas syringae, whereas KIN10 overexpression activates shoot defense pathways, increasing ROS and salicylic acid signaling at the cost of growth.
The study examined early metabolic responses to salt stress in a salt‑tolerant alfalfa cultivar, focusing on SnRK1 activity, sucrose, and trehalose‑6‑phosphate dynamics during leaf expansion. Hydroponically grown plants exposed to 200 mM NaCl showed rapid, wave‑like SnRK1 activation within 1 hour, a transient decline in chloroplast performance, and an uncoupling of the Tre6P‑sucrose regulatory link, with a second SnRK1 peak correlating with reduced leaf growth. Exogenous sucrose inhibited SnRK1 activity, highlighting early SnRK1 activation as a pivotal component of salt stress adaptation.
The study shows that silencing of NOR2 rRNA genes in Arabidopsis thaliana depends primarily on CHH-context cytosine methylation, particularly mediated by CMT2 and the chromatin remodeler DDM1, rather than CG or CHG methylation. Comparative promoter analysis revealed a prevalence of CHH sites in plant rDNA promoters, explaining why CHH methylation mutants disrupt NOR2 silencing more strongly, while NOR2 loci are hyper‑methylated and more condensed than NOR4.
The study examined transposable element (TE) silencing in the duckweed Spirodela polyrhiza, which exhibits unusually low DNA methylation, scarce 24‑nt siRNAs, and missing RdDM components. While degenerated TEs lack DNA methylation and H3K9me2, they retain heterochromatin marks H3K9me1 and H3K27me1, whereas the few intact TEs show high DNA methylation and H3K9me2, indicating a shift in RdDM focus toward potentially active TEs and suggesting heterochromatin can be maintained independently of DNA methylation in flowering plants.