Epigenetic control in plants operates through three principal channels: DNA methylation, histone modification, and non-coding RNAs. DNA methylation in rice occurs in three sequence contexts, CG, CHG and CHH, and is maintained by distinct enzymes. Chromomethylase3 handles CHG methylation, DNA Methyltransferase 1 manages CG methylation, and Domains Rearranged Methyltransferases catalyze CHH methylation. When a pathogen attacks, these methylation patterns shift, silencing genes that would otherwise help the invader and activating defense programs that would otherwise stay dormant. The review emphasizes that this is not a passive process; it is a dynamic, energy-conscious strategy that lets the plant balance the metabolic cost of immunity against the demands of growth.

At the heart of this regulatory architecture sits the RNA-directed DNA methylation pathway, or RdDM. In this pathway, the plant-specific RNA polymerases Pol IV and Pol V generate transcripts that RNA-DEPENDENT RNA POLYMERASE 2 converts into double-stranded RNA, which DICER-LIKE 3 then processes into 24-nucleotide small interfering RNAs. ARGONAUTE 4 binds these siRNAs and uses Pol V transcripts as scaffolds to recruit DRM2, the enzyme that lays down new cytosine methylation marks. Pathogen infection triggers the production of small RNAs that silence transposable elements, genomic parasites whose activation is linked to instability and disease susceptibility. Silencing these elements enhances resistance, and remarkably, the trait can be inherited by the next generation. In rice, the largest subunit of Pol IV is encoded by OsNRPD1a and OsNRPD1b; knocking these genes down produces dwarfed plants with increased tillering, reduced panicle length and, through a still-unknown pathway, enhanced disease resistance.

The review highlights WRKY45 as a striking example of multilayered epigenetic control. This transcription factor, a hub of quantitative resistance to bacterial blight, is regulated simultaneously by DNA methylation, histone modifications and small RNA pathways. A transposon-derived small RNA called TE-siR815 modulates the WRKY45 locus, and demethylation at that locus alters expression and, with it, susceptibility to Xoo. The authors argue that WRKY45-1 and WRKY45-2 function as molecular bridges connecting epigenetic control to the wholesale transcriptional reprogramming that defines the immune response against both bacterial and fungal attackers.

Concrete examples of methylation-driven resistance abound in the literature the review surveys. The famous resistance gene Xa21, which encodes a receptor kinase conferring defense against diverse Xoo strains, has a relative called Xa21G that was isolated through methylation-sensitive amplification polymorphism screening in a mutant line generated with the DNA methylation inhibitor 5-aza-2′-deoxycytidine. In wild-type plants the Xa21G promoter is methylated and its transcripts are undetectable, but in the demethylated mutant the gene is expressed. Similarly, the blast resistance gene Pib, which encodes a nucleotide-binding leucine-rich repeat protein, carries CG methylation at two promoter sites, and the PigmS gene is governed by demethylation of two tandem miniature transposons, MIT1 and MITE2, that balance tissue-specific transcription against yield. The de novo methyltransferase gene OsDRM2 regulates defense against M. oryzae, while OsRos1a, a repressor of silencing, is vital for resistance to bacterial leaf streak caused by Xanthomonas oryzae pv. oryzicola.

Histone chemistry adds a second, equally intricate layer. Activating marks such as trimethylation of histone H3 lysine 4 open chromatin and permit transcription, whereas repressive marks such as H3K27me3 seal genes shut. Rice possesses twenty Jumonji C domain histone demethylases, and several are now firmly implicated in immunity. JMJ704 promotes resistance to bacterial blight by removing H3K4me2/3 marks from negative regulators of defense, including OsWRKY62 and the susceptibility gene OsSWEET14. JMJ705, induced by stress and infection, strips H3K27me3 from defense and jasmonic acid-responsive genes; its overexpression produces a lesion-mimic phenotype and heightened Xoo resistance, while its loss diminishes resistance. On the acetylation side, the histone acetyltransferase OsHAC704 activates defense genes, whereas the deacetylases OsHDAC1 and OsHDT701 act as brakes. Knocking down OsHDAC1 enhances broad-spectrum blast resistance without stunting the plant, and the transcription factor OsGRAS30 boosts resistance by inhibiting OsHDAC1 and elevating H3K27ac levels. OsHDT701, working with the RNase P subunit Rpp30, deacetylates histone H4 at pattern-recognition and defense genes, dampening responses to both M. oryzae and Xoo. The sirtuin-like deacetylase OsSRT1 suppresses jasmonic acid biosynthesis genes, and its downregulation triggers lesion formation and hypersensitive-response gene expression, tying histone modification directly to hormone-mediated defense signaling.

Pathogens, for their part, have learned to weaponize the host’s epigenetic machinery. The secreted effector Uv1809 from the false smut fungus Ustilaginoidea virens enhances OsSRT2-mediated histone deacetylation, lowering H4K5ac and H4K8ac levels and crippling the transcriptional activation of defense genes. Host-induced silencing of Uv1809 restores resistance, demonstrating that fungal effectors actively suppress immunity by hijacking chromatin regulators. Other fungal and bacterial effectors induce histone hypoacetylation more broadly, underscoring an escalating arms race fought at the level of chromatin.

Non-coding RNAs form the third pillar. The microRNA miR7695 targets OsNRAMP6, and its overexpression increases blast resistance, while miR160a targets the auxin signaling component ARF16 and, when overexpressed, limits fungal growth and boosts hydrogen peroxide accumulation and defense gene expression. Conversely, M. oryzae induces miR319, which suppresses OsTCP21 and compromises jasmonic acid synthesis, a clear example of a pathogen exploiting a host microRNA. In the antiviral arena, ARGONAUTE 18 sequesters miR168, freeing AGO1 for antiviral RNA interference, and AGO1a overexpression confers resistance to Xoo. Viral infection suppresses miR528, unleashing its target L-ascorbate oxidase to generate reactive oxygen species for defense. Beyond microRNAs, RNA modifications are emerging as a frontier: the m6A methyltransferase MTA1 is essential for virulence in the blast fungus, and in rice the ac4C RNA modification, written by OsNAT10, undergoes infection-triggered changes that reprogram translation and activate jasmonic acid biosynthesis, a mechanism the review flags as a key discovery in plant immunity.

Perhaps the most consequential theme is epigenetic memory. DNA methylation patterns associated with resistance can persist for generations without the original pathogen stimulus, and rice plants exposed to M. oryzae show heritable methylation and histone changes that activate defense genes in their progeny. Methyl jasmonate-induced priming elevates H3K4 and H3K9 acetylation at defense gene promoters and creates chromatin-based memory of wounding. The review argues that this molecular memory, combined with emerging tools such as CRISPR-based epigenome editing, epi-breeding with natural epialleles, and high-throughput biomarker screening using bisulfite sequencing and ChIP-seq, could deliver broad-spectrum, durable resistance without the yield penalties that plague conventional approaches. Challenges remain, including the complexity of interacting epigenetic layers, potential off-target effects of editing systems, and the difficulty of validating biomarkers in a dynamic epigenome. But the authors are clear about the destination: identifying resistance-associated epigenetic markers and integrating them with traditional breeding and biotechnology offers a sustainable path to protecting rice, and global food security, against pathogens that will not stop evolving.

Subject of Research: Epigenetic regulation of rice immunity against bacterial and fungal pathogens

Article Title: Regulatory role of epigenetics in rice immunity against bacterial and fungal pathogens

Article References: Regulatory role of epigenetics in rice immunity against bacterial and fungal pathogens. (n.d.). https://doi.org/10.1007/s44297-026-00080-9

Image Credits: AI Generated

DOI: 10.1007/s44297-026-00080-9

Keywords: rice immunity, epigenetics, DNA methylation, histone modification, non-coding RNAs, RdDM, Magnaporthe oryzae, Xanthomonas oryzae, disease resistance, epigenetic breeding, CRISPR epigenome editing, food security