Expression of DORMANCY-ASSOCIATED MADS-BOX (DAM)-like genes in apple

Apple (Malus x domestica Borkh.) is a perennial woody plant that undergoes a period of dormancy (in cv. Jonathan between late September and mid-December) to survive freezing temperatures of winter. DORMANCY-ASSOCIATED MADS-BOX (DAM) genes play important roles in the regulation of growth cessation and terminal bud formation in peach. To understand the role of DAM orthologs in apple, we isolated and characterized four DAM-like genes (designated as MdDAMa, MdDAMb, MdDAMc, and MdDAMd) and monitored their expression in apical buds throughout the season by real-time quantitative polymerase chain reaction analyses. The transcription of MdDAMa peaked in October and that of MdDAMc was elevated from August to October, whereas MdDAMb and MdDAMd were practically undetectable. The tandemly arranged genes MdDAMa/MdDAMb and MdDAMc/MdDAMd were localized to chromosomes 16 and 8, respectively. Based on these observations, we infer that MdDAMa and MdDAMc acted in a dominant fashion on each locus and were correlated with the period of endodormancy.