In oranges and lemons, a chemical tag that usually turns genes off actually flips them to 'full blast.'
March 20, 2026
Original Paper
Investigation of allele-specific expression in citrus hybrids reveals the association between siRNA-mediated de novo methylation and high expression in citrus genomes
bioRxiv · 2025.07.25.666733
The Takeaway
DNA methylation is almost universally considered a 'stop' signal that prevents genes from being used. In citrus, researchers discovered that a specific type of this marking is actually required to activate genes, representing a bizarre reversal of a fundamental rule of epigenetics.
From the abstract
DNA methylation plays a central role in the regulation of gene expression. In plants, methylation occurs in the CG, CHG and CHH contexts, via distinct DNA methyltransferases including MET1, CMT3 and the RNA-directed DNA Methylation (RdDM) pathway via DRM2. In interspecific hybrids, these epigenetic mechanisms are confronted to a mixed small RNA population and two subgenomes harbouring specific methylation patterns, therefore generating unique expression profiles. The aim of this work was to unde