Rice plant response to long term CO2 enrichment: Gene expression profiling

Effects of elevated CO2 (68 Pa versus ambient 38 Pa) on gene expression were studied in rice leaves grown in soil medium with three different nitrogen conditions (0, 0.6 and 1.2 g N per 8-L pot) in CO2 controlled chambers. Soluble protein contents were slightly decreased in leaves grown under elevated CO2 regardless of N supplies, whereas the polypeptide profiles of soluble protein analyzed by 2DE using the same amount of protein were totally unchanged between ambient and elevated CO2. In contrast, gene expressions examined by microarray analyses were significantly affected by elevated CO2. Forty-six up-regulated genes (>1.5-fold) and 35 down-regulated genes (<0.68-fold) were identified and these included many signal transduction and transcription regulation related genes. By contrast, the expressions of most of the genes for primary metabolism were not significantly altered. Although changes were small, the expressions of genes for enzymes involved in CO2 fixation (carbonic anhydrase, Rubisco, phosphoglycerate kinase and glyceraldehyde-3-phosphate dehydrogenase) were down-regulated, whereas that of genes encoding enzymes for RuBP regeneration (fructose bisphosphate phosphatase, fructose bisphosphate aldolase, sedoheptulose bisphosphate phosphatase and phosphoribulokinase) and starch synthesis (ADP-glucose pyrophosphorylase and starch synthase) were up-regulated under elevated CO2. These results suggest that some sets of genes involved in primary metabolism pathway in the chloroplast are co-regulated by elevated CO2.