Bud endodormancy in woody plants plays an important role in their perennial growth cycles. We previously identified a MADS box gene, DORMANCY-ASSOCIATED MADSbox6 (PmDAM6), expressed in the endodormant lateral buds of Japanese apricot (Prunus mume), as a candidate for the dormancy-controlling gene. In this study, we demonstrate the growth inhibitory functions of PmDAM6 by overexpressing it in transgenic poplar (Populus tremula × Populus tremuloides). Transgenic poplar plants constitutively expressing PmDAM6 showed growth cessation and terminal bud set under environmental conditions in which control transformants continued shoot tip growth, suggesting the growth inhibitory functions of PmDAM6. In the Japanese apricot genome, we identified six tandemly arrayed PmDAM genes (PmDAM1–PmDAM6) that conserve an amphiphilic repression motif, known to act as a repression domain, at the carboxyl-terminal end, suggesting that they all may act as transcriptional repressors. Seasonal expression analysis and cold treatment in autumn indicated that all PmDAMs were repressed during prolonged cold exposure and maintained at low levels until endodormancy release. Furthermore, PmDAM4 to PmDAM6 responses to a short period of cold exposure appeared to vary between low- and high-chill genotypes. In the high-chill genotype, a short period of cold exposure slightly increased PmDAM4 to PmDAM6 expression, while in the low-chill genotype, the same treatment repressed PmDAM4 to PmDAM6 expression. Furthermore, PmDAM4 to PmDAM6 expression was negatively correlated with endodormancy release. We here discuss the genotype-dependent seasonal expression patterns of PmDAMs in relation to their involvement in endodormancy and variation in chilling requirements.

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.

Most deciduous fruit trees cultivated in the temperate zone require a genotype-dependent amounts of chilling exposure for dormancy release and bud break. In Japanese apricot (Prunus mume), DORMANCY-ASSOCIATED MADS-box 6 (PmDAM6) may influence chilling-mediated dormancy release and bud break. In this study, we attempted to elucidate the biological functions of PmDAM6 related to dormancy regulation by analyzing PmDAM6-overexpressing transgenic apple (Malus spp.). We generated 35S:PmDAM6 lines and chemically inducible overexpression lines, 35S:PmDAM6-GR. In both overexpression lines, shoot growth was inhibited and early bud set was observed. In addition, PmDAM6 expression repressed bud break competency during dormancy and delayed bud break. Moreover, PmDAM6 expression increased abscisic acid levels and decreased cytokinins contents during the late dormancy and bud break stages in both 35S:PmDAM6 and 35S:PmDAM6-GR. Our analysis also suggested that abscisic acid levels increased during dormancy but subsequently decreased during dormancy release whereas cytokinins contents increased during the bud break stage in dormant Japanese apricot buds. We previously revealed that PmDAM6 expression is continuously down-regulated during dormancy release toward bud break in Japanese apricot. The PmDAM6 expression pattern was concurrent with a decrease and increase in the abscisic acid and cytokinins contents, respectively, in dormant Japanese apricot buds. Therefore, we hypothesize that PmDAM6 represses the bud break competency during dormancy and bud break stages in Japanese apricot by modulating abscisic acid and cytokinins accumulation in dormant buds.

Ultraviolet-B (UV-B) light (280–315 nm) is an important environmental signal that regulates plant development and photomorphogenesis, while also affecting the flavonoid pathway, including anthocyanin biosynthesis. Regarding the effects of UV-B radiation on fruits, the effects of a short-term or postharvest irradiation on fruit quality have been well-documented, but the effects of a long-term preharvest UV-B irradiation on fruit growth and coloration remain unclear. Thus, in this study, we investigated the effects of a long-term treatment involving an environmentally relevant UV-B dose on highbush blueberry (Vaccinium corymbosum) fruit. The preharvest UV-B treatment quickly promoted fruit growth and sugar accumulation, which is not commonly observed in other fruit tree species. The UV-B exposure also accelerated fruit ripening and coloration. The dual-luciferase assay proved that in blueberries, expression ofVcUFGTencoding anthocyanin biosynthesis key enzyme, is positively and negatively regulated byVcMYBA1andVcMYBC2, respectively. Throughout the fruit development stage, the UV-B treatment up-regulatedVcMYBPA1expression, which increasedVcUFGTexpression viaVcMYBA1. In the green fruit stage, the UV-B treatment increasedHY5encoding UV receptor, which up-regulatesVcMYBPA1and down-regulatesVcMYBC2, thereby promotes the accumulation of anthocyanins. On the other hand, excessive anthocyanin synthesis was inhibited by increasedVcMYBC2levels in mature fruits when exposed to UV-B light throughHY5-independent pathway. In conclusion, anthocyanin-related MYB activators and repressor may coordinately balance the accumulation of anthocyanins in blueberry fruits, with UV-B treatments possibly influencing their effects in a stage-specific manner. The potential utility of preharvest UV-B treatments for improving blueberry fruit quality is discussed herein.

In this study, we investigated seasonal changes in protein profiles in dormant flower buds of Japanese apricot (Prunus mume Siebold Zucc.) cultivars ‘Ellching’, from subtropical Taiwan, and ‘Nanko’, from temperate Japan. One protein, isolated by two-dimensional polyacrylamide gel electrophoresis of flower bud extracts, was shown by peptide sequencing to be a dehydrin (the group of D-11 LEA (late embryogenesis-abundant) proteins). Patterns of dehydrin protein and transcript accumulation differed between the cultivars, with greater accumulations and longer persistence in ‘Nanko’ than in ‘Ellching’. These differences correspond with the greater requirement for chilling to break flower bud dormancy in ‘Nanko’ than in ‘Ellching’. Our study supports the findings of earlier work comparing dehydrin expression in the bark tissue of the evergreen and deciduous peach (Prunus persica (L.) Batsch) genotypes, and suggests that the role of dehydrin during the dormant season is common to all Prunus species.