Objective   Characteristics and expressions of Expansins, the widely existing gene family associated with plant cell wall, were studied during the fruit ripening stage to decipher the genetic functions relating to ripening of the plum fruits.

  Method   Transcriptomes of fruits of Sanyueli ( Prunus salicina Lindl.) and its red-flesh mutant were used to identify Expansin genes as well as for a bioinformatic and expression comparison of identified genes.

  Result   Thirty-three Expansins, with individual protein containing 176 to 460 amino acids, a molecular weight ranging from 19.21kD to 51.33kD, and an isoelectric point varying from 4.62 to 9.83, were identified from the fruit transcriptome data. Most of them were stable hydrophilic proteins located in the extracellular space. Phylogenetic analysis revealed that plum Expansin family included 22 EXPAs, 6 EXPBs, 1 EXPLA, and 4 EXPLBs. All of the proteins had DPBB_1 and Pollen_allerg_1 domains, and, within a same classification, they shared same conserved motif composition. Nine Expansins were differentially expressed in Sanyueli and the mutant during fruit ripening. The expressions of EVM0015785, EVM0016777, EVM0010710, EVM0022202, EVM0002390, and EVM0024996 significantly differed between Sanyueli and the red-flesh mutant.

  Conclusion   The information obtained was to be used for further study on the functions of the Expansin family during ripening of plum fruits.