Genome-wide identification and characterization of the SPL gene family in Ziziphus jujuba

SQUAMOSA Promoter-Binding Protein-Likes (SPLs) are plant specific transcription factors playing important roles in plant growth and development. The SPL gene family has been studied in various plant species; however, there is no report about SPLs in Zizyphus jujuba. In this study, we identified 18 putative ZjSPL genes in Z. jujuba using a genome-wide analysis. Sequence features, gene structures, conserved domains and motifs were analyzed. The phylogenetic relationships of SPLs in Z. jujuba and A. thaliana were revealed. A total of 5 pairs of ZjSPLs were identified, suggesting the importance of gene duplication in SPL gene expansion in Z. jujuba. In addition, 11 of the 18 ZjSPLs, belonging to G1, G2 and G5 subgroups, were found to be targets of miR156, suggesting the conservation of miR156-mediated posttranscriptional regulation in plants. Expression analysis revealed that eight ZjSPL genes were responsive to the infection of witches'-broom phytoplasma. Our results provide a basis for the further elucidation of the biological function of ZjSPLs and their regulation in witches'-broom disease.