Transcriptomic profile of Arabidopsis rosette leaves during the reproductive stage after exposure to ionizing radiation.

We attempted to obtain a transcriptomic profile of ionizing radiation-responsive genes in Arabidopsis plants using Affymetrix ATH1 whole-genome microarrays. The Arabidopsis plants were irradiated with 200 Gy gamma rays at the early reproduction stage, 33 days after sowing. Rosette leaves were harvested during the postirradiation period from 36 to 49 days after sowing and used for the microarray analysis. The most remarkable changes in the genome-wide expression were observed at 42 days after sowing (9 days after the irradiation). We identified 2165 genes as gamma-ray inducible and 1735 genes as gamma-ray repressible. These numbers of affected genes were almost two to seven times higher than those at other times. In a comparison of the control and irradiated groups, we also identified 354 differentially expressed genes as significant by applying Welch's t test and fold change analysis. The gene ontology analysis showed that radiation up-regulated defense/ stress responses but down-regulated rhythm/growth responses. Specific expression patterns of 10 genes for antioxidant enzymes, photosynthesis or chlorophyll synthesis after irradiation were also obtained using real-time quantitative PCR analysis. We discuss physiological and genetic alterations in the antioxidative defense system, photosynthesis and chlorophyll metabolism after irradiation at the reproductive stage.