Day length is a key regulator of transcriptomic responses to both CO2 and H2O2 in Arabidopsis

Growth day length, CO2 levels and H2O2 all impact plant function, but interactions between them remain unclear. Using a whole-genome transcriptomics approach, we identified gene expression patterns responding to these three factors in Arabidopsis Col-0 and the conditional catalase-deficient mutant, cat2. Plants grown for 5 weeks at high CO2 in short days (hCO2) were transferred to air in short days (SD air) or long days (LD air), and microarray data produced were subjected to three independent studies. The first two analysed genotype-independent responses. They identified 1549 genes differentially expressed after transfer from hCO2 to SD air. Almost half of these, including genes modulated by sugars or associated with redox, stress or abscisic acid (ABA) functions, as well as light signalling and clock genes, were no longer significant after transfer to air in LD. In a third study, day length-dependent H2O2-responsive genes were identified by comparing the two genotypes. Two clearly independent responses were observed in cat2 transferred to air in SD and LD. Most H2O2-responsive genes were up-regulated more strongly in SD air. Overall, the analysis shows that both CO2 and H2O2 interact with day length and photoreceptor pathways, indicating close networking between carbon status, light and redox state in environmental responses.