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.