Abstract
•In M. domestica, 83 MdMED genes were identified and characterized.•The expression pattern of MdMED subgroup-D genes was determined in different tissues at the flower induction stage.•Transcriptional levels of MdMED subgroup-D genes were explored during the flower induction period and responded to salicylic acid treatment.•MdMED81 was founded as a key regulatory mediator complex that links super-enhancers in the regulation of flowering in M. domestica.•A correlation was developed between MdMED81 and day hours that is presented in equation form, and MdMED81 model for flowering time was formed.
Mediator is a transcription factor that regulates the expression of many genes in different functional pathways, enhancing growth, development and other biological processes. Its role in flowering in Malus × domestica, however, is still unknown. Due to the long life cycle and low rate of genetic transformation in M. domestica, flowering induction is still a very serious problem, leading to lower production. Here we report the identification of 83 mediator genes in M. domestica, their gene structure, protein characteristics, locations on each chromosome, systematic phylogenetic structural analysis, distribution of the chromosome, synteny of MdMED genes, and cis-elements prediction at the promoter region of MdMED genes. On the basis of phylogenetic relationships, the members of the MdMED gene family were divided into six subgroups. Real-time quantitative PCR analysis of the MdMED subgroup-D genes displayed that most genes showed strong preferential expression in the buds and were significantly upregulated during the flower induction period. Transcriptional levels of MdMED subgroup-D genes respond to salicylic acid treatment. To determine MdMED81′s functions, we obtained MdMED81-overexpressed (OE) Arabidopsis thaliana lines that showed significantly earlier flowering compared with wild-type. Furthermore, we developed a high R2 value correlation between MdMED81 and day hours that is presented in equation form to detect MdMED81 in flowering time regulation and control in M. domestica. We also presented an annual model of MdMED81 in the control of flowering time and concluded that salicylic acid application at the right time of the year triggers MdMED81 to induce flowering in M. domestica. This data provides a new theoretical reference for the management of apple tree flowering and also provides an essential basis for future analysis of the regulation and functions of the MdMED gene family.