FLOWERING LOCUS Cdrives delayed flowering inArabidopsisgrown and selected at elevated CO₂

Summary Altered flowering time at elevated [CO 2 ] is well documented, although mechanisms are not well understood. An Arabidopsis genotype previously selected for high fitness at elevated [CO 2 ] (SG) showed delayed flowering and larger size at flowering when grown at elevated (700 ppm) versus current (380 ppm) [CO 2 ]. This response was correlated with prolonged expression of FLOWERING LOCUS C ( FLC ), a vernalization-responsive floral repressor gene. To determine if FLC directly delays flowering at elevated [CO 2 ] in SG, we used vernalization (extended cold) to downregulate FLC expression. We hypothesized that vernalization would eliminate delayed flowering at elevated [CO 2 ] through the direct reduction of FLC expression, eliminating differences in flowering time between current and elevated [CO 2 ]. We found that with downregulation of FLC expression via vernalization, SG plants grown at elevated [CO 2 ] no longer delayed flowering compared to current [CO 2 ]. Thus, vernalization returned the earlier flowering phenotype, counteracting effects of elevated [CO 2 ] on flowering. This study indicates that elevated [CO 2 ] can delay flowering directly through FLC , and downregulation of FLC under elevated [CO 2 ] reverses this effect. Moreover, this study demonstrates that increasing [CO 2 ] may potentially drive major changes in development through FLC .