FLOWERING LOCUS C drives delayed flowering in Arabidopsis grown and selected at elevated CO 2 .

Altered flowering time at elevated [CO ] is well documented, although mechanisms are not well understood. An genotype previously selected for high fitness at elevated [CO ] (SG) showed delayed flowering and larger size at flowering when grown at elevated (700 ppm) versus current (380 ppm) [CO ]. This response was correlated with prolonged expression of ( ), a vernalization-responsive floral repressor gene. To determine if directly delays flowering at elevated [CO ] in SG, we used vernalization (extended cold) to downregulate expression. We hypothesized that vernalization would eliminate delayed flowering at elevated [CO ] through the direct reduction of expression, eliminating differences in flowering time between current and elevated [CO ]. We found that with downregulation of expression via vernalization, SG plants grown at elevated [CO ] no longer delayed flowering compared to current [CO ]. Thus, vernalization returned the earlier flowering phenotype, counteracting effects of elevated [CO ] on flowering. This study indicates that elevated [CO ] can delay flowering directly through , and downregulation of under elevated [CO ] reverses this effect. Moreover, this study demonstrates that increasing [CO ] may potentially drive major changes in development through .