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The gaseous pollutant SO2 impacts deleteriously on crop growth and development.To identify genes required for SO2 stress response in maize(Zea mays.L),one highly induced mRNA encoding a D1 protein of photosystem II(ZmpsbA)was isolated by mRNA differential display.Real-time PCR analysis indicated that the transcript levels of ZmpsbA were higher in leaves and were markedly up-regulated by SO2 stress.Overexpression of ZmpsbA enhanced SO2 stress tolerance in tobacco; showing much less damage upon SO2 exposure.The transgenic tobacco lines had higher proline accumulation,but lower levels of malondialdehyde(MDA)when compared with the wild-type plants under SO2 stress.Further investigation showed that ZmpsbA transgenic plants displayed higher SOD and CAT activities,increased SOD and CAT transcript levels,and decreased reactive oxygen species(ROS)accumulation under SO2 stress.Taken together,our results demonstrate that ZmpsbA confers SO2 stress tolerance in transgenic tobacco by reducing ROS accumulation and membrane damage through enhancing the antioxidant system.ZmpsbA might serve as a candidate gene in genetic improvement for environmental pollutants(SO2 and acid rain,etc)tolerance engineering in crop plants.