FLOWERING LOCUS Cdrives delayed flowering inArabidopsisgrown and selected at elevated CO₂

Abstract

Altered flowering time at elevated [CO2] is well documented, although mechanisms are not well understood. AnArabidopsisgenotype 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 ofFLOWERING LOCUS C(FLC), a vernalization-responsive floral repressor gene. To determine ifFLCdirectly delays flowering at elevated [CO2] in SG, we used vernalization (extended cold) to downregulateFLCexpression. We hypothesized that vernalization would eliminate delayed flowering at elevated [CO2] through the direct reduction ofFLCexpression, eliminating differences in flowering time between current and elevated [CO2]. We found that with downregulation ofFLCexpression 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. This study indicates that elevated [CO2] can delay flowering directly throughFLC, and downregulation ofFLCunder elevated [CO2] reverses this effect. Moreover, this study demonstrates that increasing [CO2] may potentially drive major changes in development throughFLC.

Oligosaccharide production and signaling correlate with delayed flowering in an Arabidopsis genotype grown and selected in high [CO2]

“…Although the vernalization response pathway in addition to other floral integrator genes has been shown to be important for the [CO 2 ]-induced delay in SG [15,50], we did not note vernalization response genes to be altered here in SG. However, we noted that genes involved in the photoperiod and gibberellin-response pathways were altered.…”

“…In fall-germinating, winter-annual variants of Arabidopsis, FLC stays high until it is repressed by prolonged cold (= vernalization) [49] likely so that FT rises and flowering occurs appropriately in warm, spring conditions. In subsequent work, we confirmed that downregulation of FLC through vernalization restored early flowering in SG in elevated [CO 2 ] [50]. However, the upstream mechanisms governing the response of FLC to [CO 2 ] are unknown.…”

“…It should be noted that while we had observed the key vernalization-responsive, floralrepressor gene, FLC, to prolong its elevated expression in SG and that its expression contributed to flowering delays [15,50], FLC did not show differences in either CG or SG at the time point harvested, here. This may be due to the detection method used as we noted significant variation among samples.…”

“…However, as we were interested in mechanisms controlling flowering, and whether there was a relationship between carbohydrate-mediated pathways and flowering-control mechanisms, we also assessed whether there were differences in the flowering genes independently. We assessed a list of 156 genes known to be associated with flowering [67] (S4 [71], which was previously shown to be upregulated by elevated [CO 2 ] in both genotypes either independently or interactively with vernalization [15,50]. LFY and FUL are regulated by micro RNA 156-regulated SPL transcription factors [72,73], which in turn, are modified by T6P [25], and SOC1, LFY, and FUL were altered in a trehalose 6-phosphate synthase 1 (tps1) mutant [74], suggesting one mechanism through which [CO 2 ]-induced carbohydrate changes may alter flowering.…”

“…However, the upstream mechanisms governing the response of FLC to [CO 2 ] are unknown. Additionally, another flowering pathway may also be altered by [CO 2 ] change, as LFY was altered in both SG and CG, at least partially independently of FLC [15,50].…”