PHO2(encoding a ubiquitin-conjugating E2 enzyme),a negative regulator of phosphate transporter PHT1,is known to play a key role in the maintenance of phosphate homeostasis.In this study,nine members of ZmPHO2 gene family were identified from whole genome sequence of maize inbred line B73 based on PHO2 orthologs in Arabidopsis thaliana and Oryza sativa,which can be subdivided into at least three clusters based on phylogenetic relationship among several plants.The complete CDSs of all PHO2 homologs have been cloned from maize inbred line 178,and the conserved domain analysis revealed that all proteins have the same topology and harbor an ubiquitin-conjugating E2 enzyme catalytic domain (UBCc) which is fabricated of about 130 amino acids residues including a conserved cysteine.Based on quantitative real-time PCR,the transcripts of all ZmPHO2 genes were detected and exhibited different expression profiles in different organs and genotypes under low phosphate stress,but there are no distinct expression profiles among most of genes in the same tissue.Among them,ZmPHO2;H2 showed decreased expression levels in roots and increased expression levels in leaves at all sampled time points in maize inbred line 9782,indicating that ZmPHO2;H2 in maize may be involved in the regulation of phosphate transport from leaves to roots in order to maintain phosphorus homeostasis between the shoot and the root.