To better understand the expression and function of the High Mobility Group Protein B (HMGB) family genes in Arabidopsis,we cloned the first five genes encoding HMGB proteins in Arabidopsis thaliana genome:AtHMGB1,AtHMGB2,AtHMGB3,AtHMGB4 and AtHMGB5.Real-time reverse transcription-PCR (RT-PCR) analysis was employed to determine the transcript levels of HMGB genes accurately in Arabidopsis wild-type under plant phytohormone treatment.Binary vectors carrying the AtHMGB2,AtHMGB4 and AtHMGB5 genes were transformed into Arabidopsis to detect the phenotype of the transgenic Arabidopsis induced by ABA.Our results proved that AtHMGB2 was more abundantly expressed than other family members,whereas AtHMGB4 and AtHMGB5 were more abundantly expressed in roots and flowers than in stems and leaves.The expression level of the AtHMGB family genes were markedly regulated by ABA induction,especially the AtHMGB2.Under ABA treatment,the transgenic Arabidopsis plants that over-expressed AtHMGB2 displayed retarded germination and subsequent growth compared with the wild-type Arabidopsis.Overexpression of AtHMGB4 and AtHMGB5 had little impact on seed germination and seedling growth of the plants by ABA induction.Taken together,these results provide a novel basis for understanding the biological functions of AtHMGB family members under ABA conditions.