The involvement of the phytohormone ethylene in the adaptation of Arabidopsis rosettes to enhanced atmospheric carbon dioxide concentrations

Abstract: Atmospheric CO2 levels are rising rapidly due to anthropogenic activities. Although plants require CO2 to fuel photosynthesis, the relationship between CO2 and plant growth is complex. In phytotrons elevated CO2 was shown to stimulate growth of Arabidopsis thaliana. In nature, there is, however, a constant variation in temperature, the availability of sunlight, nutrients and water, in addition to biotic stresses. The aim of this study was to explore the impact of elevated CO2 on rosette growth and transcriptome profiles in Arabidopsis plants grown under natural radiation and air temperature. Because of its regulatory function in cell elongation, photosynthesis, stomatal closure and leaf senescence, the importance of ethylene for the response to elevated CO2 was investigated in wild-type plants (Col-0), and in plants with constitutive or reduced ethylene signaling (ctr1-1 and ein2-5, respectively). Rosette area measurements indicated that increased atmospheric CO2 did not increase vegetative growth in any of the genotypes. Moreover, both Col-0 and ein2-5 plants grown at elevated CO2 exhibited an increase in stress responsive gene expression compared to those grown at ambient CO2. A down-regulation of photosynthesis and an upregulation of metabolism were, apart from the overrepresentation of stress genes, the most important responses to elevated CO2 in both wild-type and ethylene-insensitive plants. However, whereas in Col-0 starch biosynthesis and turnover were more strongly activated, lipid metabolism was enhanced in ein2-5. Through stomatal closure, sugar and lipid metabolism and leaf senescence, ethylene could be involved in the adaption of Arabidopsis rosettes to elevated CO2