Dormancy-associated MADS-box Genes Research Articles

Histone modifications affecting plant dormancy and dormancy release: common regulatory effects on hormone metabolism.

As sessile organisms, plants enter periods of dormancy in response to environmental stresses to ensure continued growth and reproduction in future. During dormancy, plant growth is suppressed, adaptive/survival mechanisms are exerted, and stress tolerance increases over a prolonged period until the plants resume their development or reproduction under favorable conditions. In this review, we focus on seed dormancy and bud dormancy, which are critical for adaptations to fluctuating environmental conditions. We provide an overview of the physiological characteristics of both types of dormancy as well as the importance of the phytohormones abscissic acid and gibberellin for establishing and releasing dormancy, respectively. Additionally, recent epigenetic analyses have revealed that dormancy establishment and release are associated with the removal and deposition of histone modifications at the loci of key regulatory genes influencing phytohormone metabolism and signaling, including DELAY OF GERMINATION 1 and DORMANCY-ASSOCIATED MADS-box genes. We discuss our current understanding of the physiological and molecular mechanisms required to establish and release seed dormancy and bud dormancy, while also describing how environmental conditions control dormancy depth, with a focus on the effects of histone modifications.

Peculiarity of transcriptional and H3K27me3 dynamics during peach bud dormancy

Bud dormancy facilitates the survival of meristems under harsh environmental conditions. To elucidate how molecular responses to chilling accumulation controlling dormancy in peach buds, chromatin immunoprecipitation sequencing to identify the H3K27me3 modifications and RNA sequencing of two peach cultivars with pronounced differences in chilling requirement were carried out, the results showed that genes associated with abscisic acid and gibberellic acid signal pathways play key roles in dormancy regulation. The results demonstrated that peach flower bud differentiation occurred continuously in both cultivars during chilling accumulation, which was correlated with the transcript abundance of key genes involved in phytohormone metabolism and flower bud development under adverse conditions. The more increased strength in high chilling-requirement cultivar along with the chilling accumulation at the genome-wide level. The function of the dormancy-associated MADS-box gene PpDAM6 was identified, which is involved in leaf bud break in peach and flower development in transgenic Nicotiana tabacum (NC89). In addition, PpDAM6 was positively regulated by PpCBF, and the genes of putative dormancy-related and associated with metabolic pathways were proposed. Taken together, these results constituted a theoretical basis for elucidating the regulation of peach bud dormancy transition.

Genome of tetraploid sour cherry (Prunus cerasus L.) 'Montmorency' identifies three distinct ancestral Prunus genomes.

Sour cherry (Prunus cerasus L.) is a valuable fruit crop in the Rosaceae family and a hybrid between progenitors closely related to extant Prunus fruticosa (ground cherry) and Prunus avium (sweet cherry). Here we report a chromosome-scale genome assembly for sour cherry cultivar Montmorency, the predominant cultivar grown in the USA. We also generated a draft assembly of P. fruticosa to use alongside a published P. avium sequence for syntelog-based subgenome assignments for 'Montmorency' and provide compelling evidence P. fruticosa is also an allotetraploid. Using hierarchal k-mer clustering and phylogenomics, we show 'Montmorency' is trigenomic, containing two distinct subgenomes inherited from a P. fruticosa-like ancestor (A and A') and two copies of the same subgenome inherited from a P. avium-like ancestor (BB). The genome composition of 'Montmorency' is AA'BB and little-to-no recombination has occurred between progenitor subgenomes (A/A' and B). In Prunus, two known classes of genes are important to breeding strategies: the self-incompatibility loci (S-alleles), which determine compatible crosses, successful fertilization, and fruit set, and the Dormancy Associated MADS-box genes (DAMs), which strongly affect dormancy transitions and flowering time. The S-alleles and DAMs in 'Montmorency' and P. fruticosa were manually annotated and support subgenome assignments. Lastly, the hybridization event 'Montmorency' is descended from was estimated to have occurred less than 1.61 million years ago, making sour cherry a relatively recent allotetraploid. The 'Montmorency' genome highlights the evolutionary complexity of the genus Prunus and will inform future breeding strategies for sour cherry, comparative genomics in the Rosaceae, and questions regarding neopolyploidy.

The study of the characteristics of the secondary flowering of Cerasus subhirtella 'Autumnalis'.

The short flowering period of ornamental cherry trees is the main factor limiting their use in gardens. Determining the secondary flowering characteristics of ornamental cherry trees is required to prolong their flowering period. In this experiment, Cerasus subhirtella 'Autumnalis' was used as the experimental material. The phenological differences in their annual growth cycle were observed using the BBCH coding system. The cooling requirements of the flower buds were evaluated by the chilling hours model (temperature between 0 and 7.2 °C) and the Utah model. The expression of the core gene involved in bud dormancy regulation DAM (dormancy-associated MADS-box) from the completion of flower bud differentiation in one year until the following year was measured by performing real-time fluorescence-based quantitative PCR. The results showed that the flowering duration of C. subhirtella 'Autumnalis' from November to December was longer than that of C. yedoensis 'Somei Yoshino', which was from March to April. The progress from seed bud-break to flower bud opening took about 10 days for C. subhirtella 'Autumnalis', while the same stage for C. yedoensis 'Somei Yoshino' took around 20 days. Additionally, the flower buds of C. subhirtella 'Autumnalis' needed only the chilling temperature unit of 54.08 to satisfy the chilling requirement, while C. yedoensis 'Somei Yoshino' required a chilling temperature unit of 596.75. After the completion of flower bud differentiation, during low-temperature storage, the expression of DAM4 and DAM5 genes first increased and then decreased, whereas, the expression of the DAM6 gene continued to decrease, and the expression of DAM4, DAM5, and DAM6 in C. yedoensis 'Somei Yoshino' increased rapidly and was maintained at a high level. This showed that the upregulation of the expression of the DAM4, DAM5, and DAM6 genes can inhibit the flower bud germination of Cherry Blossom. The relative expression of the DAM gene of C. subhirtella 'Autumnalis' was significantly lower than that of the DAM gene of C. yedoensis 'Somei Yoshino' from the end of October to the beginning of December, leading to its secondary flowering in autumn. These results might elucidate why the flower buds of C. subhirtella 'Autumnalis' can break their internal dormancy and bloom in the autumn and then again in the following year. Our findings might provide a reference for conducting further studies on the mechanisms of secondary flowering and bud dormancy in cherries.

Evolutionary origin and functional specialization of Dormancy-Associated MADS box (DAM) proteins in perennial crops

BackgroundBud dormancy is a phenological adaptation of temperate perennials that ensures survival under winter temperature conditions by ceasing growth and increasing cold hardiness. SHORT VEGETATIVE PHASE (SVP)-like factors, and particularly a subset of them named DORMANCY-ASSOCIATED MADS-BOX (DAM), are master regulators of bud dormancy in perennials, prominently Rosaceae crops widely adapted to varying environmental conditions.ResultsSVP-like proteins from recently sequenced Rosaceae genomes were identified and characterized using sequence, phylogenetic and synteny analysis tools. SVP-like proteins clustered in three clades (SVP1–3), with known DAM proteins located within SVP2 clade, which also included Arabidopsis AGAMOUS-LIKE 24 (AthAGL24). A more detailed study on these protein sequences led to the identification of a 15-amino acid long motif specific to DAM proteins, which affected protein heteromerization properties by yeast two-hybrid system in peach PpeDAM6, and the unexpected finding of predicted DAM-like genes in loquat, an evergreen species lacking winter dormancy. DAM gene expression in loquat trees was studied by quantitative PCR, associating with inflorescence development and growth in varieties with contrasting flowering behaviour.ConclusionsPhylogenetic, synteny analyses and heterologous overexpression in the model plant Arabidopsis thaliana supported three major conclusions: 1) DAM proteins might have emerged from the SVP2 clade in the Amygdaloideae subfamily of Rosaceae; 2) a short DAM-specific motif affects protein heteromerization, with a likely effect on DAM transcriptional targets and other functional features, providing a sequence signature for the DAM group of dormancy factors; 3) in agreement with other recent studies, DAM associates with inflorescence development and growth, independently of the dormancy habit.

Populus SVL Acts in Leaves to Modulate the Timing of Growth Cessation and Bud Set.

SHORT VEGETATIVE PHASE (SVP) is an important regulator of FLOWERING LOCUS T (FT) in the thermosensory pathway of Arabidopsis. It is a negative regulator of flowering and represses FT transcription. In poplar trees, FT2 is central for the photoperiodic control of growth cessation, which also requires the decrease of bioactive gibberellins (GAs). In angiosperm trees, genes similar to SVP, sometimes named DORMANCY-ASSOCIATED MADS-BOX genes, control temperature-mediated bud dormancy. Here we show that SVL, an SVP ortholog in aspen trees, besides its role in controlling dormancy through its expression in buds, is also contributing to the regulation of short day induced growth cessation and bud set through its expression in leaves. SVL is upregulated during short days in leaves and binds to the FT2 promoter to repress its transcription. It furthermore decreases the amount of active GAs, whose downregulation is essential for growth cessation, by repressing the transcription of GA20 oxidase. Finally, the SVL protein is more stable in colder temperatures, thus integrating the temperature signal into the response. We conclude that the molecular function of SVL in the photoperiodic pathway has been conserved between Arabidopsis and poplar trees, albeit the physiological process it controls has changed. SVL is thus both involved in regulating the photoperiod response in leaves, modulating the timing of growth cessation and bud set, and in the subsequent temperature regulation of dormancy in the buds.

High-quality genome assembly of 'Cuiguan' pear (Pyrus pyrifolia) as a reference genome for identifying regulatory genes and epigenetic modifications responsible for bud dormancy

Dormancy-associated MADS-box (DAM) genes serve as crucial regulators of the endodormancy cycle in rosaceous plants. Although pear DAM genes have been identified previously, the lack of a high-quality reference genome and techniques to study gene function have prevented accurate genome-wide analysis and functional verification of such genes. Additionally, the contribution of other genes to the regulation of endodormancy release remains poorly understood. In this study, a high-quality genome assembly for 'Cuiguan' pear (Pyrus pyrifolia), which is a leading cultivar with a low chilling requirement cultivated in China, was constructed using PacBio and Hi-C technologies. Using this genome sequence, we revealed that pear DAM genes were tandemly clustered on Chr8 and Chr15 and were differentially expressed in the buds between 'Cuiguan' and the high-chilling-requirement cultivar 'Suli' during the dormancy cycle. Using a virus-induced gene silencing system, we determined the repressive effects of DAM genes on bud break. Several novel genes potentially involved in the regulation of endodormancy release were identified by RNA sequencing and H3K4me3 chromatin immunoprecipitation sequencing analyses of 'Suli' buds during artificial chilling using the new reference genome. Our findings enrich the knowledge of the regulatory mechanism underlying endodormancy release and chilling requirements and provide a foundation for the practical regulation of dormancy release in fruit trees as an adaptation to climate change.

Structure and Expression of Bud Dormancy-Associated MADS-Box Genes (DAM) in European Plum.

Bud dormancy in temperate perennials ensures the survival of growing meristems under the harsh environmental conditions of autumn and winter, and facilitates an optimal growth and development resumption in the spring. Although the molecular pathways controlling the dormancy process are still unclear, DORMANCY-ASSOCIATED MADS-BOX genes (DAM) have emerged as key regulators of the dormancy cycle in different species. In the present study, we have characterized the orthologs of DAM genes in European plum (Prunus domestica L.). Their expression patterns together with sequence similarities are consistent with a role of PdoDAMs in dormancy maintenance mechanisms in European plum. Furthermore, other genes related to dormancy, flowering, and stress response have been identified in order to obtain a molecular framework of these three different processes taking place within the dormant flower bud in this species. This research provides a set of candidate genes to be genetically modified in future research, in order to better understand dormancy regulation in perennial species.

Thermal-responsive genetic and epigenetic regulation of DAM cluster controlling dormancy and chilling requirement in peach floral buds

The Dormancy-associated MADS-box (DAM) gene cluster in peach serves as a key regulatory hub on which the seasonal temperatures act and orchestrate dormancy onset and exit, chilling response and floral bud developmental pace. Yet, how different temperature regimes interact with and regulate the six linked DAM genes remains unclear. Here, we demonstrate that chilling downregulates DAM1 and DAM3–6 in dormant floral buds with distinct patterns and identify DAM4 as the most abundantly expressed one. We reveal multiple epigenetic events, with tri-methyl histone H3 lysine 27 (H3K27me3) induced by chilling specifically in DAM1 and DAM5, a 21-nt sRNA in DAM3 and a ncRNA induced in DAM4. Such induction is inversely correlated with downregulation of their cognate DAMs. We also show that the six DAMs were hypermethylated, associating with the production of 24-nt sRNAs. Hence, the chilling-responsive dynamic of the different epigenetic elements and their interactions likely define distinct expression abundance and downregulation pattern of each DAM. We further show that the expression of the five DAMs remains steadily unchanged or continuously downregulated at the ensuing warm temperature after chilling, and this state of regulation correlates with robust increase of sRNA expression, H3K27me3 and CHH methylation, which is particularly pronounced in DAM4. Such robust increase of repressive epigenetic marks may irreversibly reinforce the chilling-imposed repression of DAMs to ensure flower-developmental programming free from any residual DAM inhibition. Taken together, we reveal novel information about genetic and epigenetic regulation of the DAM cluster in peach, which will be of fundamental significance in understanding of the regulatory mechanisms underlying chilling requirement and dormancy release, and of practical application for improvement of plasticity of flower time and bud break in fruit trees to adapt changing climates.

Dormancy-Associated MADS-Box (DAM) Genes Influence Chilling Requirement of Sweet Cherries and Co-Regulate Flower Development with SOC1 Gene.

Floral bud dormancy release of fruit tree species is greatly influenced by climate change. The lack of chilling accumulation often results in the occurrence of abnormal flower and low yields of sweet cherries (Prunus avium L.) in warm regions. To investigate the regulation of dormancy in sweet cherries, six DAM genes with homology to peach DAM, designated PavDAM1-6, have been identified and characterized. Phylogenetic analysis indicate that these genes are similar to DAMs in peach, apple and pear. The expression patterns of the PavDAMs in the low-chill cultivar ‘Royal Lee’ were different from that in the high-chill cultivar ‘Hongdeng’. ‘Royal Lee’ exhibits lower transcriptional level of PavDAM1 compared to ‘Hongdeng’, especially at the stage of chilling accumulation, and transcriptional levels of PavDAM4/5 were high in both cultivars during the endodormancy. Ectopic expression of PavDAM1 and PavDAM5 in Arabidopsis resulted in plants with abnormal flower and seed development, especially the PavDAM5. Higher transcriptional levels of SOC1 were observed in transgenic PavDAM1/5 lines, and ectopic expression of PavSOC1 had the similar floral phenotype. Further, protein interaction analysis demonstrated that PavDAM1/5 could interact with PavSOC1 in vivo and in vitro, which will help clarify the molecular mechanism of the flower development in sweet cherry or other fruit trees.

Effects of chilling accumulation on DORMANCY-ASSOCIATED MADS-box gene expressions in ‘Satonishiki’ sweet cherry

Bud dormancy allows most temperate fruit tree species, including sweet cherry (Prunus avium), to avoid cold injury and synchronize their annual growth patterns. The progression of bud dormancy release is influenced by environmental factors, including chilling accumulation. Global climate changes may affect bud dormancy release, resulting in an irregular bud break. Thus, a more thorough characterization of dormancy is required. The peach (Prunus persica) and Japanese apricot (Prunus mume) genomes contain at least six DORMANCY-ASSOCIATED MADS-box (DAM) genes that may have important roles related to bud dormancy regulation. The DAM gene expression levels are diverse among species. For example, peach DAM1, 2, and 4 expression levels are up-regulated during terminal bud formation, while peach and P. mume DAM5 and 6 expression levels are down-regulated during dormancy release. In this study, we first identified six sweet cherry DAM genes (PavDAM1-6) by mapping short-read transcript sequences for dormant 'Satonishiki' flower buds against reference gene sequences (PmDAM1-6). We then conducted quantitative real-time polymerase chain reaction analyses of PavDAM4-6 expression in 'Satonishiki' lateral buds collected at low-, medium-, and high-chill regions in Japan between November and March. PavDAM4 expression was first up-regulated as chilling accumulated and then down-regulated. In contrast, PavDAM6 expression was down-regulated from November onward. The expression of PavDAM4 was up-regulated faster at high- and medium-chill locations than at the low-chill location where chilling accumulated slowly. The PavDAM5-6 expression patterns were similar at all three locations. These results suggest that chilling treatments induce distinct changes to the expression of PavDAM genes.

I Want to (Bud) Break Free: The Potential Role of DAM and SVP-Like Genes in Regulating Dormancy Cycle in Temperate Fruit Trees.

Bud dormancy is an adaptive process that allows trees to survive the hard environmental conditions that they experience during the winter of temperate climates. Dormancy is characterized by the reduction in meristematic activity and the absence of visible growth. A prolonged exposure to cold temperatures is required to allow the bud resuming growth in response to warm temperatures. In fruit tree species, the dormancy cycle is believed to be regulated by a group of genes encoding MADS-box transcription factors. These genes are called DORMANCY-ASSOCIATED MADS-BOX (DAM) and are phylogenetically related to the Arabidopsis thaliana floral regulators SHORT VEGETATIVE PHASE (SVP) and AGAMOUS-LIKE 24. The interest in DAM and other orthologs of SVP (SVP-like) genes has notably increased due to the publication of several reports suggesting their role in the control of bud dormancy in numerous fruit species, including apple, pear, peach, Japanese apricot, and kiwifruit among others. In this review, we briefly describe the physiological bases of the dormancy cycle and how it is genetically regulated, with a particular emphasis on DAM and SVP-like genes. We also provide a detailed report of the most recent advances about the transcriptional regulation of these genes by seasonal cues, epigenetics and plant hormones. From this information, we propose a tentative classification of DAM and SVP-like genes based on their seasonal pattern of expression. Furthermore, we discuss the potential biological role of DAM and SVP-like genes in bud dormancy in antagonizing the function of FLOWERING LOCUS T-like genes. Finally, we draw a global picture of the possible role of DAM and SVP-like genes in the bud dormancy cycle and propose a model that integrates these genes in a molecular network of dormancy cycle regulation in temperate fruit trees.

Transcriptome analysis and metabolic profiling reveal the key role of α-linolenic acid in dormancy regulation of European pear.

Deciduous trees require sufficient chilling during winter dormancy to grow. To decipher the dormancy-regulating mechanism, we carried out RNA sequencing (RNA-Seq) analysis and metabolic profiling of European pear (Pyrus communis L.) vegetative buds during the dormancy phases. Samples were collected from two cultivars that differed greatly in their chilling requirements: 'Spadona' (SPD), a low chilling requirement cultivar; and Harrow Sweet (HS), a high chilling requirement cultivar. Comparative transcriptome analysis revealed >8500 differentially expressed transcripts; most were related to metabolic pathways. Out of 174 metabolites, 44 displayed differential levels in both cultivars, 38 were significantly changed only in SPD, and 15 only in HS. Phospholipids were mostly accumulated at the beginning of dormancy, sugars between before dormancy and mid-dormancy, and fatty acids, including α-linolenic acid, at dormancy break. Differentially expressed genes underlying previously identified major quantitative trait loci (QTLs) in linkage group 8 included genes related to the α-linolenic acid pathway, 12-oxophytodienoate reductase 2-like, and the DORMANCY-ASSOCIATED MADS-BOX (DAM) genes, PcDAM1 and PcDAM2, putative orthologs of PpDAM1 and PpDAM2, confirming their role for the first time in European pear. Additional new putative dormancy-related uncharacterized genes and genes related to metabolic pathways are suggested. These results suggest the crucial role of α-linolenic acid and DAM genes in pear bud dormancy phase transitions.

Monitoring Dormancy Transition in Almond [Prunus Dulcis (Miller) Webb] during Cold and Warm Mediterranean Seasons through the Analysis of a DAM (Dormancy-Associated MADS-Box) Gene

For fruit tree (Prunus) species, flower bud dormancy completion determines the quality of bud break and the flowering time. In the present climate change and global warming context, the relationship between dormancy and flowering processes is a fundamental goal in molecular biology of these species. In almond [P. dulcis (Miller) Webb], flowering time is a trait of great interest in the development of new cultivars adapted to different climatic areas. Late flowering is related to a long dormancy period due to high chilling requirements of the cultivar. It is considered a quantitative and highly heritable character but a dominant gene (Late bloom, Lb) was also described. A major QTL (quantitative trait loci) in the linkage group (LG) 4 was associated with Lb, together with other three QTLs in LG1 and LG7. In addition, DAM (Dormancy-Associated MADS-Box) genes located in LG1 have been largely described as a gene family involved in bud dormancy in different Prunus species including peach [P. persica (L.) Batsch] and Japanese apricot (P. mume Sieb. et Zucc.). In this work, a DAM transcript was cloned and its expression was analysed by qPCR (quantitative Polymerase Chain Reaction) in almond flower buds during the dormancy release. For this purpose two almond cultivars (‘Desmayo Largueta’ and ‘Penta’) with different chilling requirements and flowering time were used, and the study was performed along two years. The complete coding sequence, designated PdDAM6 (Prunus dulcis DAM6), was subjected to a phylogenetic analysis with homologous sequences from other Prunus species. Finally, expression dynamics analysed by using qPCR showed a continuous decrease in transcript levels for both cultivars and years during the period analysed. Monitoring almond flower bud dormancy through DAM expression should be used to improve almond production in different climate conditions.

Expression analysis of apple DORMANCY-ASSOCIATED MADS-box genes in buds during dormancy release

Expression analysis of apple DORMANCY-ASSOCIATED MADS-box genes in buds during dormancy release

Transcriptome Profiles Reveal the Crucial Roles of Hormone and Sugar in the Bud Dormancy of Prunus mume

Bud dormancy transition is a vital developmental process for perennial plant survival. The process is precisely regulated by diverse endogenous genetic factors and environmental cues, but the mechanisms are not yet fully understood. Prunus mume is an ideal crop for bud dormancy analysis because of its early spring-flowering characteristics and small sequenced genome. Here, we analyzed the transcriptome profiles at the three endodormancy stages and natural flush stage using RNA sequencing combined with phytohormone and sugar content measurements. Significant alterations in hormone contents and carbohydrate metabolism have been observed, and α-amylases, Glucan Hydrolase Family 17 and diphosphate-glycosyltransferase family might play crucial roles in the interactions between hormones and sugars. The following hypothetical model for understanding the molecular mechanism of bud dormancy in Prunus mume is proposed: low temperatures exposure induces the significant up-regulation of eight C-repeat binding factor genes, which directly promotes all six dormancy-associated MADS-box genes, resulting in dormancy establishment. The prolonged cold and/or subsequently increasing temperature then decreases the expression levels of these two gene families, which alleviates the inhibition of FLOWERING LOCUS T and reopens the growth-promoting pathway, resulting in dormancy release and the initiation of the bud break process.

Comprehensive Cloning of Prunus mume Dormancy Associated MADS-Box Genes and Their Response in Flower Bud Development and Dormancy.

Dormancy Associated MADS-box genes are SVP/MADs-box members and supposed to play crucial roles in plant dormancy of perennial species. In Prunus mume, PmDAM6 has been previously identified to induce plant dormancy. In the current study, six PmDAMs were cloned in P. mume and functionally analyzed in yeast and tobacco to detect the roles of the genes paralogous to PmDAM6. The expression patterns together with sequence similarities indicate that PmDAMs are divided into two sub-clades within SVP group. Moreover, PmDAMs are verified to take part in the development of different plant organs, specifically the flower buds, in some intricate patterns. Furthermore, the PmDAM proteins are found to have special functions by forming corresponding protein complex during the development of flower bud and induction of dormancy. In particular, when PmDAM1 dominating in flower bud in the warm months, the protein complexes are consisted of PmDAM1 itself or with PmDAM2. With the decrease temperatures in the following months, PmDAM6 was found to be highly expressed and gradually changed the complex structure to PmDAM6-protein complex due to strong binding tendencies with PmDAM1 and PmDAM3. Finally, the homodimers of PmDAM6 prevailed to induce the dormancy. The results obtained in the current study highlight the functions of PmDAMs in the tissue development and dormancy, which provide available suggestions for further explorations of protein-complex functions in association with bud growth and dormancy.

Candidate gene association with summer dormancy in tall fescue

Two main types of summer dormancy in tall fescue [Schedonorus arundinaceus (Schreb.) Dumort] are recognized, eco-dormancy and endo-dormancy. Endo-dormancy is a physiological response to environmental signals leading to slowing of metabolic activity in meristematic tissues and most likely controlled by circadian clock genes. Therefore, it is genetically inherited and allelic variation among and between summer-dormant and non-dormant varieties is expected. The main objective of this study was to explore the association between dormancy and various candidate genes. Twenty-three genes were amplified and sequenced in two dormant and two non-dormant checks. Nucleotide variants unique to each group were converted to kompetitive allele specific PCR markers and were tested on 52 dormant and non-dormant accessions. Five markers, from the genes CONSTANS and TERMINAL FLOWER showed significant associations (R2 = 0.10 to 0.13, p < 0.05) with field phenotypic scores. These two genes are known to modulate meristem determinacy and growth, suggesting that meristem determinacy is probably one of the mechanisms involved in summer dormancy in tall fescue. Another five markers showed significant associations with the surrogate germination phenotype (R2 = 0.13 to 0.20, p < 0.05). One marker originated from dormancy-associated MADS-box gene sequence, three markers originated from auxin response factors sequences, and one marker was derived from heat shock proteins sequences. These results confirm the implication of photoperiod and temperature in the regulation of summer dormancy. A selection index combining these markers may be valuable for the differentiation between dormant and non-dormant tall fescue genotypes.

Simultaneous down-regulation of DORMANCY-ASSOCIATED MADS-box6 and SOC1 during dormancy release in Japanese apricot (Prunus mume) flower buds

ABSTRACTIn temperate deciduous fruit crops such as Prunus spp., bud endodormancy is an important physiological phase affecting the timing of blooming and subsequent fruit development. Japanese apricot (Prunus mume) bears unmixed flower buds, separate from vegetative buds, that bloom slightly more than a month before vegetative bud burst. Seasonal expression of Prunus mume DORMANCY ASSOCIATED MADS-box genes (PmDAMs) has previously been analyzed only in vegetative buds, with an association between these genes and flower bud endodormancy release not yet confirmed. In this study, we performed a seasonal expression analysis of PmDAM1–6 genes in flower buds of two Japanese apricot genotypes – namely, high-chill and low-chill cultivars. The analysis revealed that PmDAM3, PmDAM5, and PmDAM6 expressions are closely associated with dormancy release in both flower and vegetative buds. In addition, a yeast two-hybrid screening demonstrated that PmDAM6 can interact in yeast with the homolog of Arabidopsis SOC1 (PmSOC1). Synchronized expression patterns were detected in PmDAM6 and PmSOC1 during dormancy release in flower buds of the two genotypes. Taken together, these results suggest that the dimer of PmDAM6 and PmSOC1 may play a role in the regulation of dormancy transition and blooming time in Japanese apricot flower buds.

Structural genomics and transcriptional characterization of the Dormancy-Associated MADS-box genes during bud dormancy progression in apple

The molecular control of bud dormancy establishment and release is still not well understood, although some genes have already been demonstrated to play important roles in this process. The dormancy-associated MADS-box (DAM) genes were first identified in the peach EVERGROWING locus and are considered the main regulators of bud dormancy control. In this work, the apple (Malus × domestica Borkh.), a perennial plant adapted to temperate climates that displays cycles of growth and bud dormancy, was screened for the presence of DAM genes. The candidate genes retrieved were characterized in comparison to DAM genes from other species. Four of them (MdDAM1–4) are structurally very similar to the reported DAM genes. When apple genomic segments containing these candidates were compared to the peach EVERGROWING locus, a highly conserved noncoding region was detected inside their largest intron. Similar sequences were also identified inside introns of apricot and pear DAM genes. Organ expression patterns revealed that MdDAM1–4 are mainly expressed in dormant buds and seeds, with low transcript accumulation in vegetative structures. In addition, the MdDAM genes showed seasonally oscillating patterns of steady-state messenger RNA (mRNA) levels and were downregulated by artificial chilling. Motif analyses in the promoter and in the intronic conserved region of the MdDAM genes disclosed some clues to the regulation of the expression patterns observed. Possible roles for the conserved intronic sequence in dormancy regulation are discussed.