Abstract
In the present study, we identified and characterized the apricot (Prunus armeniaca L.) homologs of three dormancy-related genes, namely the ParCBF1 (C-repeat binding factor), ParDAM5 (dormancy-associated MADS-BOX) and ParDAM6 genes. All highly conserved structural motifs and the 3D model of the DNA-binding domain indicate an unimpaired DNA-binding ability of ParCBF1. A phylogenetic analysis showed that ParCBF1 was most likely homologous to Prunus mume and Prunus dulcis CBF1. ParDAM5 also contained all characteristic domains of the type II (MIKCC) subfamily of MADS-box transcription factors. The homology modeling of protein domains and a phylogenetic analysis of ParDAM5 suggest its functional integrity. The amino acid positions or small motifs that are diagnostic characteristics of DAM5 and DAM6 were determined. For ParDAM6, only a small part of the cDNA was sequenced, which was sufficient for the quantification of gene expression. The expression of ParCBF1 showed close association with decreasing ambient temperatures in autumn and winter. The expression levels of ParDAM5 and ParDAM6 changed according to CBF1 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 ParDAM5 and ParDAM6 genes in dormancy induction and maintenance. Cultivars with higher CR and delayed flowering time showed higher expression levels of ParDAM5 and ParDAM6 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.
Highlights
Many important fruit tree species belong to the Prunus genus of the Rosaceae family
For the isolation of the intron-less ParCBF1 gene, genomic DNA was extracted from the leaves of an additional apricot cultivar, “Korai zamatos,” while ParDAM5 and ParDAM6 sequences containing several introns were amplified from cDNA obtained from ‘Zard’ flower buds
CMIII-1, 2, and 4 are located downstream of AP2 domain, while CMIII-3 includes the PKKR/PAGR and DSAWR motifs flanking the AP2 domain on the 5 and 3 ends, respectively. These results show that ParCBF1 shares significant homology with other Prunus C-repeat Binding Factor (CBF) and has the structural motifs required for its biological function
Summary
Many important fruit tree species belong to the Prunus genus of the Rosaceae family. Flower bud development is one of the most critical stages in their reliable production. The annual growing cycle of temperate woody plants forms an integrated system with subsequent phases of active growth and dormancy (Perry, 1971; Lloret et al, 2018). During dormancy plants exhibit little or no growth and their metabolic activity decreases for a period of time. It is an essential strategy for perennial plants to survive harmful environmental conditions during winter (Hanninen and Tanino, 2011). Endodormancy is a genetically controlled mechanism that is triggered in early autumn by external factors and inhibits bud development even under growth-promoting conditions. Plants require a certain amount of chill for endodormancy-release to enter ecodormancy phase when bud growth is only prevented by unfavorable climatic conditions
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