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

Abstract 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 (C 1 ) metabolites, including formate, but their contribution to cellular C 1 metabolism has remained unclear. DNA methylation is an important epigenetic modification that depends on methyl groups provided by folate-mediated C 1 metabolism. Here we show that photorespiration supplies C 1 units for DNA methylation in Arabidopsis . We demonstrate that carbon from formate is incorporated into 5-methylcytosine through the C 1 -tetrahydrofolate synthase pathway, which operates predominantly during the day. Elevated CO 2 that suppresses photorespiration alters the methylome, especially when the serine-derived C 1 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 CO 2 levels and other environmental influences on photorespiration.