The present invention relates to an isolated polynucleotide capable of giving a plant tolerance to drought and/or salt stress, which comprises a polynucleotide sequence as shown in SEQ ID NO:1, and to a promoter capable of giving a plant tolerance to drought and/or salt stress. The present invention also relates to an expression vector comprising the said polynucleotide and/or the said promoter, and to a host cell transformed or transfected by the said expression vector. The present invention further relates to a use of the said polynucleotide or promoter sequence in improvement of plant tolerance to drought and/or salt stress.