Genomic identification and expression profiles during callus formation of LBD transcription factor genes in sweet orange (Citrus sinensis) and functional characterization of CsLBD17

Lateral organ boundaries domain (LBD) is a plant-specific transcription factor. Here, we identified 37 LBD genes of sweet orange in the CPBD database, which were unevenly distributed on 7 chromosomes, and most of those were located in the nucleus. All CsLBD genes were divided into class I (31) containing five subclasses, and class II (6) containing two subclasses and associated with plant growth and development, plant hormones, defense and stress response. WGD/segmental duplication events primarily were confrimed to promote the development of the CsLBD gene family. CsLBDs were more strongly correlated with dicotyledonous plants than with monocotyledonous plants. Gene expression analysis showed that CsLBD16 and CsLBD17 genes in segment stem cultured in callus induction medium were higher than those in the other two media without auxin throughout the cultivation process. The N-terminal region of the CsLBD17 protein is responsible for the transcriptional activation of CsLBD17. Arabidopsis thaliana with overexpression of CsLBD17 showed stronger callus formation ability on CIM medium and stronger root growth ability on MS medium, indicating that it plays an important role in the development of calluses and roots.