Genome-wide identification of LBD transcription factors in apple and the function of MdLBD16a in adventitious rooting and callus development

Abstract

The plant-specific LBD transcription factors play crucial roles in plant growth and development. In this study, 67 MdLBDs were identified in apple by whole genome bioinformatics analysis. According to gene structure and phylogenetic analysis, the MdLBD gene family was divided into Class I (57) and Class II (10). Due to whole genome duplication, the number of LBD genes in apple was much greater than in other plants in the Rosaceae family. The LBD29/LBD16 locus was conserved in the Rosaceae plants, but with different orientations. Many cis-acting regulatory elements relative to plant growth and development and responses to the environment, growth regulators and abiotic/biotic stressors were enriched in the MdLBD promoters. Some MdLBDs showed organ-specific expression. MdLBD16a was significantly up-regulated during adventitious root formation, peaking seven days after auxin treatment. MdLBD16a was localized in the nucleus. Overexpression of MdLBD16a in tomato increased the number of adventitious roots. Auxin promoted callus growth in MdLBD16a-overexpressing callus. MdLBD16a played dual roles in root primordium formation and callus development. We propose that plants with the LBD29/LBD16 locus have adventitious root and lateral root development that depend on the LBD29/LBD16 network. These comprehensive analyses of these MdLBDs provided valuable resources for further functional study in apple and other species.