Identification, Structural and Functional Characterization of Dormancy Regulator Genes in Apricot (Prunus armeniaca L.)

Abstract

In the present study, we identified and characterized the apricot (<i>Prunus armeniaca</i> L.) homologs of three dormancy-related genes, namely the <i>ParCBF1</i> (<i>C-repeat binding factor</i>), <i>ParDAM5</i> (<i>dormancy-associated MADS-BOX</i>) and <i>ParDAM6</i> genes. All highly conserved structural motifs and the 3D model of the DNA-binding domain indicate an unimpaired DNA-binding ability of <i>Par</i>CBF1. A phylogenetic analysis showed that <i>ParCBF1</i> was most likely homologous to <i>Prunus mume</i> and <i>Prunus dulcis CBF1</i>. <i>Par</i>DAM5 also contained all characteristic domains of the type II (MIKC^C) subfamily of MADS-box transcription factors. The homology modeling of protein domains and a phylogenetic analysis of <i>ParDAM5</i> suggest its functional integrity. The amino acid positions or small motifs that are diagnostic characteristics of DAM5 and DAM6 were determined. For <i>ParDAM6</i>, only a small part of the cDNA was sequenced, which was sufficient for the quantification of gene expression. The expression of <i>ParCBF1</i> showed close association with decreasing ambient temperatures in autumn and winter. The expression levels of <i>ParDAM5</i> and <i>ParDAM6</i> changed according to <i>CBF1</i> expression rates and the fulfillment of cultivar chilling requirements (CR). The concomitant decrease of gene expression with endodormancy release is consistent with a role of <i>ParDAM5</i> and <i>ParDAM6</i> genes in dormancy induction and maintenance. Cultivars with higher CR and delayed flowering time showed higher expression levels of <i>ParDAM5</i> and <i>ParDAM6</i> toward the end of endodormancy. Differences in the timing of anther developmental stages between early- and late-flowering cultivars and two dormant seasons confirmed the genetically and environmentally controlled mechanisms of dormancy release in apricot generative buds. These results support that the newly identified apricot gene homologs have a crucial role in dormancy-associated physiological mechanisms.