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The present study investigated the expressional regulation of PpDAM5 and PpDAM6, two of the six peach (Prunus persica) dormancy-associated MADS-box genes, in relation to lateral bud endodormancy. PpDAM5 and PpDAM6 were originally identified as homologues of Arabidopsis SHORT VEGETATIVE PHASE/AGAMOUS-LIKE 24 identified in the EVERGROWING locus of peach. Furthermore, PpDAM5 and PpDAM6 have recently been suggested to be involved in terminal bud dormancy. In this study, seasonal expression analyses using leaves, stems, and lateral buds of high-chill and low-chill peaches in field conditions indicated that both genes were up-regulated during the endodormancy period and down-regulated with endodormancy release. Controlled environment experiments showed that the expression of both PpDAM5 and PpDAM6 were up-regulated by ambient cool temperatures in autumn, while they were down-regulated by the prolonged period of cold temperatures in winter. A negative correlation between expression levels of PpDAM5 and PpDAM6 and bud burst percentage was found in the prolonged cold temperature treatment. Application of the dormancy-breaking reagent cyanamide to endo/ecodormant lateral buds induced early bud break and down-regulation of PpDAM5 and PpDAM6 expression at the same time. These results collectively suggest that PpDAM5 and PpDAM6 may function in the chilling requirement of peach lateral buds through growth-inhibiting functions for bud break.

To understand the molecular basis of the endodormancy of buds of perennial plants, we searched for the genes that are expressed preferentially in endodormant lateral buds of the deciduous fruit tree japanese apricot (Prunus mume Sieb. et Zucc.) using suppression subtractive hybridization with mirror orientation selection (SSH/MOS). We generated two SSH/MOS libraries containing gene pools that are expressed preferentially in endodormant buds in comparison with paradormant or ecodormant buds to search for the genes that are upregulated by endodormancy induction or down-regulated by endodormancy release, respectively. Differential screening and sequencing indicated that genes involved in gibberellin metabolism, stress resistance, cell wall modification, and signal transduction, such as transcription factors, are upregulated in endodormant buds. After a further expression survey and full-length cDNA cloning, we found that a gene similar to the SVP/AGL24-type MADS-box transcription factor showed endodormancy-associated expression. Seasonal expression analysis suggested that the SVP/AGL24 homolog in japanese apricot might be involved in endodormancy regulation of its lateral buds.

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This study investigated the regulation of the seasonal expression of PpDAM5 and PpDAM6, two of the six peach (Prunus persica) dormancy-associated MADS-box genes, in relation to the endodormancy and development of lateral vegetative and flower buds of low-and high-chill peach cultivars. PpDAM5 and PpDAM6 were originally found as homologs of Arabidopsis SVP/AGL24 at the EVERGROWING (EVG) locus of peach and have been recently shown to be involved in lateral bud endodormancy. Seasonal expression analyses in this study indicated that PpDAM5 and PpDAM6 transcript levels in lateral vegetative buds of both low-and high-chill cultivars in the field negatively correlated with bud burst percentages determined under forcing conditions. Negative correlation was also found between their transcript levels and the flower organ enlargement rate. These results suggest that distinct seasonal expression patterns of PpDAM5 and PpDAM6 are correlated with a distinct chilling requirement for bud break and flowering of low-and high-chill cultivars. Characterization of the genomic structure of PpDAM5 and PpDAM6 revealed the presence of large insertions in the first introns of both PpDAM5 and PpDAM6 in low-chill peach. Alteration of the genomic structure is discussed with respect to the low-chill character.