PNNL

Abstract

Since the onset of industrialization, the atmospheric CO2 ([CO2]) has increased from 270 to 415 ppm and is projected to reach 800-1000 ppm this century. Some Arabidopsis ecotypes delayed flowering in future, elevated [CO2] relative to current [CO2], while others showed no change or accelerations. Therefore, future flowering behaviors cannot be predicted by extrapolating past trends forward; we must understand the mechanisms driving flowering response to rising [CO2]. Photosynthesis often increases under elevated [CO2] in C3 plants, altering carbohydrates. Carbohydrate levels can be sensed within plants and exogenous application of carbohydrates influences flowering time and transcript levels associated with flowering. We asked: how do global changes in carbohydrates and transcription correlate with changes in flowering time under elevated [CO2]? We used a genotype (SG) of Arabidopsis that was selected for high fitness at elevated [CO2] (700 ppm). SG displays delayed flowering under elevated [CO2] (700 ppm) relative to current [CO2] (400 ppm). We compared SG to a closely related control genotype (CG) that does not alter flowering in response to [CO2] shifts. We compared metabolomic and transcriptomic profiles in SG and CG at current and elevated [CO2] to assess correlations with flowering in these conditions. While both genotypes altered some carbohydrates in response to elevated [CO2], SG had higher levels of sucrose than CG and showed a stronger increase in glucose and fructose in response to elevated [CO2]. Both genotypes demonstrated transcriptional changes, with CG increasing genes related to breakdown of fructose 1,6-bisphosphate, the synthesis of amino acids, and secondary metabolites; and SG decreasing genes related to starch and sugar metabolism, but increasing genes involved in oligosaccharide production and sugar modifications. Genes associated with flowering regulation within the photoperiod, vernalization, and meristem identity response pathways were altered in these genotypes. Elevated [CO2] is likely acting through carbohydrate changes to influence transcription in both genotypes, and delayed flowering in SG. Changes in the oligosaccharide pool may contribute to delayed flowering in SG. This work extends the body of work exploring genotypic-specific flowering responses to elevated [CO2] in Arabidopsis.