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 found that facultative pseudogamous gametophytic apomixis is the predominant reproductive mode in natural populations of the polyploid fruit tree Psidium cattleyanum f. lucidum in Uruguay, with the proportion of apomictic versus sexual reproduction varying among populations and ploidy levels. Flow cytometric seed screening combined with microsatellite genotyping revealed mainly clonal progeny that nonetheless retain high genetic variability and strong population structure, indicating that ploidy influences reproductive strategy and genetic patterns.
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 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 generated two allotriploid Brassica hybrids (ArAnCn) to investigate asymmetric subgenome dominance, finding that the Cn subgenome dominates despite the An subgenome showing highest expression levels. Increased density of accessible chromatin regions (ACRs) in the Cn subgenome correlates with dominant gene expression, while changes in CHH methylation and specific RNA‑directed DNA methylation pathway mutants affect subgenome bias.
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 57 global accessions of the invasive hybrid Kalanchoe xhoughtonii and its parents, revealing extensive cytogenetic and genomic variation among morphotypes but identifying a single tetraploid genotype (morphotype A) that dominates worldwide. This genotype exhibits remarkable genetic uniformity, high phenotypic plasticity, and prolific vegetative propagation, illustrating how hybridization and polyploidy can drive rapid invasive success.
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.