Photorespiration is linked to DNA methylation by formate as a one-carbon source

Photorespiration is a costly cellular process that reduces photosynthetic efficiency. While mitigating photorespiratory losses could boost crop yields, the interconnection of photorespiration with other processes is increasingly recognized. Its high carbon turnover generates mitochondrial one-carbon (C₁) metabolites, including formate, but their contribution to cellular C₁ metabolism has remained unclear. DNA methylation is an important epigenetic modification that depends on methyl groups provided by folate-mediated C₁ metabolism. Here we show that photorespiration supplies C₁ units for DNA methylation in Arabidopsis. We demonstrate that carbon from formate is incorporated into 5-methylcytosine through the C₁-tetrahydrofolate synthase pathway, which operates predominantly during the day. Elevated CO₂ that suppresses photorespiration alters the methylome, especially when the serine-derived C₁ supply, which compensates for a blocked formate-derived supply, is compromised. These findings establish a metabolic link between photorespiration and epigenome stability and provide a framework for understanding methylome dynamics under rising CO₂ levels and other environmental influences on photorespiration.