FLOWERING LOCUS C drives delayed flowering in Arabidopsis grown and selected at elevated CO2

O_LIAltered flowering time at elevated [CO2] is well documented, although mechanisms are not well understood. An Arabidopsis genotype previously selected for high fitness at elevated [CO2] (SG) showed delayed flowering and larger size at flowering when grown at elevated (700 ppm) versus current (380 ppm) [CO2]. This response was correlated with prolonged expression of FLOWERING LOCUS C (FLC), a vernalization-responsive floral repressor gene. C_LIO_LITo determine if FLC directly delays flowering at elevated [CO2] in SG, we used vernalization (extended cold) to downregulate FLC expression. We hypothesized that vernalization would eliminate delayed flowering at elevated [CO2] through the direct reduction of FLC expression, eliminating differences in flowering time between current and elevated [CO2]. C_LIO_LIWe found that with downregulation of FLC expression via vernalization, SG plants grown at elevated [CO2] no longer delayed flowering compared to current [CO2]. Thus, vernalization returned the earlier flowering phenotype, counteracting effects of elevated [CO2] on flowering. C_LIO_LIThis study indicates that elevated [CO2] can delay flowering directly through FLC, and downregulation of FLC under elevated [CO2] reverses this effect. Moreover, this study demonstrates that increasing [CO2] may potentially drive major changes in development through FLC. C_LI