Effect of small coding genes on the circadian rhythms under elevated CO₂ conditions in plants

Increase in atmospheric carbon dioxide (CO₂) has a significant effect on plant growth and development. To explore the elevated-CO₂ response, we generated transcriptional profiles over a time course (2 h-14 days) of exposure to elevated CO₂ in Arabidopsis thaliana. Genes related to photosynthesis were down-regulated and circadian rhythm-related genes were abnormally regulated in the early to middle phase of elevated CO₂ exposure. To understand the novel mechanism of elevated CO₂ signaling, we focused on 42 unknown small coding genes that showed differential expression patterns under elevated CO₂ conditions. Four transgenic plants overexpressing the small coding gene exhibited a growth-defective phenotype under elevated CO₂ but not under current CO₂. Transcriptome analysis showed that circadian rhythm-related genes were commonly regulated in four transgenic plants. These circadian rhythm-related genes were transcribed in the dark when CO₂ concentrations in the leaf was high. Taken together, our identified four small coding genes are likely to participate in elevated CO₂ signaling to the circadian rhythm.