The plant response to high CO 2 levels is heritable and orchestrated by DNA methylation.

Plant responses to abiotic environmental challenges are known to have lasting effects on the plant beyond the initial stress exposure. Some of these lasting effects are trans-generational, affecting the next generation. The plant response to elevated carbon dioxide (CO 2 ) levels has been well studied. However, these investigations are typically limited to plants grown for a single generation in a high CO 2 environment while trans-generational studies are rare. We aimed to determine trans-generational growth responses in plants after exposure to high CO 2 by investigating the direct progeny when returned to baseline CO 2 levels. We found that both the flowering plant Arabidopsis thaliana and seedless non-vascular plant Physcomitrium patens continue to display accelerated growth rates in the progeny of plants exposed to high CO 2 . We used the model species Arabidopsis to dissect the molecular mechanism and found that DNA methylation pathways are necessary for heritability of this growth response. More specifically, the pathway of RNA-directed DNA methylation is required to initiate methylation and the proteins CMT2 and CMT3 are needed for the trans-generational propagation of this DNA methylation to the progeny plants. Together, these two DNA methylation pathways establish then maintain a cellular memory to high CO 2 exposure.