Abstract: One mutant line named eto(enhanced tolerance to osmotic stress),with salt tolerance was screened from a T-DNA insertion mutant collection of Arabidopsis thaliana.TAIL-PCR analysis showed that T-DNA tag insertion in the eto was located at nucleotide 27502 in BAC F3M18,upstream(at position-487 relative to the translation initiation codon) of gene At1g77740(encoding a putative phosphatidylinositol-4-phosphate 5-kinase,AtPIP5K2).In addition to a reduced rate of seed germination,NaCl also inhibited the growth and the greening of cotyledons of wild-type seedlings,but not the eto mutant.This inserted mutation co-segregated closely with the eto phenotype.AtPIP5K2 was amplified by RT-PCR from the total RNA of wild type plants.Sequence analysis revealed that the cDNA full-length is 2 265 bp encoding a protein of 755 amino acids.When deduced amino acid sequences were compared with homologous sequences from other organisms,AtPIP5K2 was found sharing much higher sequence similarity(62%—75%) with plant PIPKs genes than with PIPKs genes of other organisms(33%—37% similarity).In addition,AtPIP5K2 also contained two highly conserved motifs "PIPKc","MORN repeat",which were identical to those of other PIPKs from plants.Another analysis not only indicated that AtPIP5K2 transcript was expressed predominantly in roots and rosette leaves,but also showed the insertion resulted in higher accumulation of the AtPIP5K2 in mutant plants,and this change may play an essential role in the tolerance to the osmotic stress.