Bud Endodormancy Research Articles

Comparison of phytohormone levels and transcript profiles during seasonal dormancy transitions in underground adventitious buds of leafy spurge.

Leafy spurge (Euphorbia esula L.) is an herbaceous perennial weed that maintains its perennial growth habit through generation of underground adventitious buds (UABs) on the crown and lateral roots. These UABs undergo seasonal phases of dormancy under natural conditions, namely para-, endo-, and ecodormancy in summer, fall, and winter, respectively. These dormancy phases can also be induced in growth chambers by manipulating photoperiod and temperature. In this study, UABs induced into the three phases of dormancy under controlled conditions were used to compare changes in phytohormone and transcriptome profiles. Results indicated that relatively high levels of ABA, the ABA metabolite PA, and IAA were found in paradormant buds. When UABs transitioned from para- to endodormancy, ABA and PA levels decreased, whereas IAA levels were maintained. Additionally, transcript profiles associated with regulation of soluble sugars and ethylene activities were also increased during para- to endodormancy transition, which may play some role in maintaining endodormancy status. When crown buds transitioned from endo- to ecodormancy, the ABA metabolites PA and DPA decreased significantly along with the down-regulation of ABA biosynthesis genes, ABA2 and NCED3. IAA levels were also significantly lower in ecodormant buds than that of endodormant buds. We hypothesize that extended cold treatment may trigger physiological stress in endodormant buds, and that these stress-associated signals induced the endo- to ecodormancy transition and growth competence. The up-regulation of NAD/NADH phosphorylation and dephosphorylation pathway, and MAF3-like and GRFs genes, may be considered as markers of growth competency.

Applying paclobutrazol at dormancy induction inhibits shoot apical meristem activity during terminal bud development in Picea mariana seedlings

Applying paclobutrazol at dormancy induction inhibited shoot apical meristem mitotic activity, thereby decreasing rate and duration of needle-primordium initiation and thus needle-primordium number in terminal buds of Picea mariana seedlings. The effect of applying various rates of paclobutrazol (an inhibitor of gibberellic acid biosynthesis) at dormancy induction on shoot apical meristem activity during terminal bud development in first-year Picea mariana Mill. (B.S.P.) seedlings was investigated. During needle-primordium initiation, mitotic activity was reduced in shoot apical meristems of treated seedlings compared with control seedlings. The reduction was most evident within the peripheral zone where primordia arose but also occurred within the apical zone, which provides cells to the peripheral zone. The reduced mitotic activity within the peripheral zone coincided with a decrease in both rate and duration of needle-primordium initiation on nascent embryonic shoots within terminal buds in treated seedlings compared with control seedlings. Moreover, meristems of treated seedlings were smaller, shorter, and narrower (determined by cell counts as another measure of mitotic activity) compared with control seedlings. Thus, these meristems had less available space for needle-primordium initiation. As a result, embryonic shoots in treated seedlings had fewer needle primordia compared with control seedlings. Furthermore, onset of bud endodormancy (delimited by an absence of mitotic activity within the shoot apical meristem after completion of needle-primordium initiation) was realized in treated seedlings before the last sampling date, whereas it was not realized in control seedlings by the last sampling date.

Can phenological models predict tree phenology accurately in the future? The unrevealed hurdle of endodormancy break.

The onset of the growing season of trees has been earlier by 2.3days per decade during the last 40years in temperate Europe because of global warming. The effect of temperature on plant phenology is, however, not linear because temperature has a dual effect on bud development. On one hand, low temperatures are necessary to break bud endodormancy, and, on the other hand, higher temperatures are necessary to promote bud cell growth afterward. Different process-based models have been developed in the last decades to predict the date of budbreak of woody species. They predict that global warming should delay or compromise endodormancy break at the species equatorward range limits leading to a delay or even impossibility to flower or set new leaves. These models are classically parameterized with flowering or budbreak dates only, with no information on the endodormancy break date because this information is very scarce. Here, we evaluated the efficiency of a set of phenological models to accurately predict the endodormancy break dates of three fruit trees. Our results show that models calibrated solely with budbreak dates usually do not accurately predict the endodormancy break date. Providing endodormancy break date for the model parameterization results in much more accurate prediction of this latter, with, however, a higher error than that on budbreak dates. Most importantly, we show that models not calibrated with endodormancy break dates can generate large discrepancies in forecasted budbreak dates when using climate scenarios as compared to models calibrated with endodormancy break dates. This discrepancy increases with mean annual temperature and is therefore the strongest after 2050 in the southernmost regions. Our results claim for the urgent need of massive measurements of endodormancy break dates in forest and fruit trees to yield more robust projections of phenological changes in a near future.

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.

Extensive Transcriptome Changes During Natural Onset and Release of Vegetative Bud Dormancy in Populus.

To survive winter, many perennial plants become endodormant, a state of suspended growth maintained even in favorable growing environments. To understand vegetative bud endodormancy, we collected paradormant, endodormant, and ecodormant axillary buds from Populus trees growing under natural conditions. Of 44,441 Populus gene models analyzed using NimbleGen microarrays, we found that 1,362 (3.1%) were differentially expressed among the three dormancy states, and 429 (1.0%) were differentially expressed during only one of the two dormancy transitions (FDR p-value < 0.05). Of all differentially expressed genes, 69% were down-regulated from paradormancy to endodormancy, which was expected given the lower metabolic activity associated with endodormancy. Dormancy transitions were accompanied by changes in genes associated with DNA methylation (via RNA-directed DNA methylation) and histone modifications (via Polycomb Repressive Complex 2), confirming and extending knowledge of chromatin modifications as major features of dormancy transitions. Among the chromatin-associated genes, two genes similar to SPT (SUPPRESSOR OF TY) were strongly up-regulated during endodormancy. Transcription factor genes and gene sets that were atypically up-regulated during endodormancy include a gene that seems to encode a trihelix transcription factor and genes associated with proteins involved in responses to ethylene, cold, and other abiotic stresses. These latter transcription factors include ETHYLENE INSENSITIVE 3 (EIN3), ETHYLENE-RESPONSIVE ELEMENT BINDING PROTEIN (EBP), ETHYLENE RESPONSE FACTOR (ERF), ZINC FINGER PROTEIN 10 (ZAT10), ZAT12, and WRKY DNA-binding domain proteins. Analyses of phytohormone-associated genes suggest important changes in responses to ethylene, auxin, and brassinosteroids occur during endodormancy. We found weaker evidence for changes in genes associated with salicylic acid and jasmonic acid, and little evidence for important changes in genes associated with gibberellins, abscisic acid, and cytokinin. We identified 315 upstream sequence motifs associated with eight patterns of gene expression, including novel motifs and motifs associated with the circadian clock and responses to photoperiod, cold, dehydration, and ABA. Analogies between flowering and endodormancy suggest important roles for genes similar to SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL), DORMANCY ASSOCIATED MADS-BOX (DAM), and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1).

Saffron: Its Phytochemistry, Developmental Processes, and Biotechnological Prospects.

The present state of knowledge concerning developmental processes and the secondary metabolism of saffron, Crocus sativus L. (Iridaceae), along with the genes involved in these processes so far known, is reviewed. Flowers and corms constitute the most valuable parts of saffron. Corm and flower development are two key aspects to be studied in saffron to increase the yield and quality of the spice, to raise its reproductive rate, and to implement new production systems. Important knowledge about the physiology of flowering and vegetative growth has been acquired in recent years, but there is still only limited information on molecular mechanisms controlling these processes. Although some genes involved in flower formation and meristem transition in other species have been isolated in saffron, the role of these genes in this species awaits further progress. Also, genes related with the synthesis pathway of abscisic acid and strigolactones, growth regulators related with bud endodormancy and apical dominance (paradormancy), have been isolated. However, the in-depth understanding of these processes as well as of corm development is far from being achieved. By contrast, saffron phytochemicals have been widely studied. The different flower tissues and the corm have been proved to be an important source of phytochemicals with pharmacological properties. The biotechnological prospects for saffron are here reviewed on the basis of the discovery of the enzymes involved in key aspects of saffron secondary metabolism, and we also analyze the possibility of transferring current knowledge about flowering and vegetative propagation in model species to the Crocus genus.

COLD ACCLIMATION PATTERNS OF ACTINIDIA ARGUTE CULTIVARS IN A TEMPERATE CLIMATE ZONE

The kiwi berry, Actinidia arguta Planch is gaining importance in temperate Europe. Warm transient intervals during the winter season can initiate cold deacclimation and bud break of woody plants. Most A. arguta cultivars are characterised by an early bud burst which may result in horticultural limitations due to a high sensitivity to spring frost of these young shoots/inflorescences. The evolution of bud dormancy was observed in two Actinidia arguta 'Weiki' and 'Geneva' cultivars. From September through mid-October the final 30-day shooting percentage (FS) was low. Between mid-October and mid-December a steep rise in FS indicates that bud endodormancy was broken. 'Weiki' appears to have a lesser need for cold exposure in order to release it from dormancy. The seasonal pattern of cold acclimation and deacclimation was determined for both cultivars using the electrolyte leakage test. Maximal cold tolerance was achieved in midwinter. In early spring cold tolerance of the buds declined again. 'Geneva' was more cold tolerant than 'Weiki'.

Physiological and Biochemical Processes of Magnolia wufengensis in Response to Foliar Abscisic Acid Application during Natural Cold Acclimation

The rare species Magnolia wufengensis frequently suffers from freezing injury in northern China. To investigate the influence of exogenous abscisic acid (ABA) application on the natural cold acclimation of M. wufengensis, physiological and biochemical changes in field-grown M. wufengensis seedlings subjected to foliar ABA treatments at four concentrations (0, 300, 600, and 900 mg·L−1) were evaluated from Sept. 2012 to Jan. 2013. The optimum foliar application concentrations of ABA for M. wufengensis were between 600 and 900 mg·L−1, which led to faster shoot growth cessation, leaf senescence, and development rates of bud endodormancy level and shoot freezing tolerance. The improved freezing tolerance under exogenous ABA application was associated with promoted dehydration and accumulation of proline, soluble protein, and certain soluble sugars such as glucose and fructose. Foliar ABA treatments initiated a cascade of steps for advancing the cold acclimation process of M. wufengensis. We suggest that exogenous ABA application may be used on M. wufengensis grown in northern China, where there are short growing seasons and early fall frost events.

SEX EXPRESSION IN DIOSPYROS: PHENOLOGICAL CONTROL OF FLOWER BUD DEVELOPMENT IN D. KAKI AND D. LOTUS

Blooming time of persimmon (Diospyros kaki: 2n=6x=90) and its synchronicity are often associated with bud endodormancy. The objective of our study is to understand the molecular mechanism of dormancy and flowering in persimmon. To this end, we attempted to use date plum (D. lotus: 2n=2x=30) as a model of persimmon because molecular and genetic studies in persimmon are often hindered by high ploidy level of persimmon. Here, seasonal flower bud development was observed, using D. kaki ‘Hiratanenashi’ and ‘Zenjimaru’, which bear only female flowers and both female and male flowers, respectively, as well as male and female trees of D. lotus ‘Kunsenshi’. Buds were collected monthly and the internal flower development was observed using scanning electron microscope. Visible flower meristem initiation was commenced by the middle and the end of June in D. lotus and D. kaki, respectively. Following the flower meristem initiation, calyx differentiation progressed during autumn and winter season in D. lotus and D. kaki. However, a prominent progress in petal and stamen/pistil formation was not observed until after endodormancy break both in D. lotus and D. kaki. These results demonstrated that phenological control of flower bud development was similar between these species, suggesting that D. lotus can be used as a model plant for studying dormancy and floral development in persimmon.

&lt;b&gt;Dormancy of 'Imperial Gala' apple and 'Hosui' pear tree buds in a region of low chill occurrence

The objective of this work was to evaluate the dormancy dynamic of Imperial Gala apple tree buds and Hosui pear tree buds in a region of low chill occurrence. Experiments were conducted between April and August in 2007 and 2008. Branches were collected every two weeks from an orchard at Porto Amazonas (Parana State, Brazil). On the last sampling day, an additional set of branches was collected and refrigerated between 4°C and 7°C for 1,440 hours. Dormancy was evaluated using a biological test of single node cuttings isolated in growth chambers (GC) at 25°C with 16 hours of light exposure. The number of chill hours (CH) and chill units (CU) for the region were recorded. The two species were evaluated in separate experiments. We used 11 completely randomized treatments with four replicas for each species. The peak of endodormancy for the Imperial Gala apple tree buds occurred in early June 2007 and from middle June to early July in 2008. The endodormancy of the Hosui pear tree buds oscillated between April and August in 2007 and peaked between June and early July in 2008.

The resemblance and disparity of gene expression in dormant and non-dormant seeds and crown buds of leafy spurge (Euphorbia esula).

BackgroundLeafy spurge (Euphorbia esula L.) is a herbaceous perennial weed and dormancy in both buds and seeds is an important survival mechanism. Bud dormancy in leafy spurge exhibits three well-defined phases of para-, endo- and ecodormancy; however, seed dormancy for leafy spurge is classified as physiological dormancy that requires after-ripening and alternating temperature for maximal germination. Overlaps in transcriptome profiles between different phases of bud and seed dormancy have not been determined. Thus, we compared various phases of dormancy between seeds and buds to identify common genes and molecular processes, which should provide new insights about common regulators of dormancy.ResultsCluster analysis of expression profiles for 201 selected genes indicated bud and seed samples clustered separately. Direct comparisons between buds and seeds are additionally complicated since seeds incubated at a constant temperature of 20°C for 21 days (21d C) could be considered paradormant (Para) because seeds may be inhibited by endosperm-generated signals, or ecodormant (Eco) because seeds germinate after being subjected to alternating temperature of 20:30°C. Since direct comparisons in gene expression between buds and seeds were problematic, we instead examined commonalities in differentially-expressed genes associated with different phases of dormancy. Comparison between buds and seeds (‘Para to Endo buds’ and ‘21d C to 1d C seeds’), using endodormant buds (Endo) and dormant seeds (1d C) as common baselines, identified transcripts associated with cell cycle (HisH4), stress response/transcription factors (ICE2, ERFB4/ABR1), ABA and auxin response (ABA1, ARF1, IAA7, TFL1), carbohydrate/protein degradation (GAPDH_1), and transport (ABCB2). Comparison of transcript abundance for the ‘Eco to Endo buds’ and ‘21d C to 1d C seeds’ identified transcripts associated with ABA response (ATEM6), auxin response (ARF1), and cell cycle (HisH4). These results indicate that the physiological state of 21d C seeds is more analogous to paradormant buds than that of ecodormant buds.ConclusionCombined results indicate that common molecular mechanisms associated with dormancy transitions of buds and seeds involve processes associated with ABA and auxin signaling and transport, cell cycle, and AP2/ERF transcription factors or their up-stream regulators.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0216-4) contains supplementary material, which is available to authorized users.

Molecular cloning and expression analysis of tea plant aquaporin (AQP) gene family

The role of aquaporin proteins (AQPs) has been extensively studied in plants. However, the information of AQPs in the tea plant (Camellia sinensis) is unclear. In this manuscript, we isolated 20 full-length AQP cDNAs from the tea plant, and these sequences were classified into five subfamilies. The genes in these subfamilies displayed differential expression profiles in the studied tissues. The CsAQP expression patterns correlated with flower development and opening (FDO) and bud endodormancy (BED). To better understand the short-term expression patterns of CsAQPs in response to abiotic stress, tea plants were treated with abscisic acid (ABA), cold, salt or drought. ABA treatment down-regulated the expression of various CsAQPs. Salt up-regulated the transcription of most CsAQP genes. Cold treatment resulted in a complicated transcriptional regulation pattern for various CsAQPs. The expression of CsAQPs, especially plasma membrane intrinsic proteins (CsPIPs) and tonoplast intrinsic proteins (CsTIPs), was induced by drought and remained relatively high after rehydration in leaves, whereas almost all the CsAQPs were repressed in roots. Our results highlighted the diversity of CsAQPs in the tea plant and demonstrated that the CsPIP and CsTIP genes play a vital role in the stress response as well as in FDO and BED. Furthermore, certain CsSIPs (small basic intrinsic proteins), CsNIPs (NOD26-like intrinsic proteins) and CsXIPs (X intrinsic proteins) may regulate BED and FDO.

Roles of endoplasmic reticulum stress and unfolded protein response associated genes in seed stratification and bud endodormancy during chilling accumulation in Prunus persica.

Dormancy mechanisms in seeds and buds arrest growth until environmental conditions are optimal for development. A genotype-specific period of chilling is usually required to release dormancy, but the underlying molecular mechanisms are still not fully understood. To discover transcriptional pathways associated with dormancy release common to seed stratification and bud endodormancy, we explored the chilling-dependent expression of 11 genes involved in endoplasmic reticulum stress and the unfolded protein response signal pathways. We propose that endoplasmic reticulum stress and the unfolded protein response impact on seed as well as bud germination and development by chilling-dependent mechanisms. The emerging discovery of similarities between seed stratification and bud endodormancy status indicate that these two processes are probably regulated by common endoplasmic reticulum stress and unfolded protein response signalling pathways. Clarification of regulatory pathways common to both seed and bud dormancy may enhance understanding of the mechanisms underlying dormancy and breeding programs may benefit from earlier prediction of chilling requirements for uniform blooming of novel genotypes of deciduous fruit tree species.

Identification and expression analysis of candidate genes related to endodormancy induction and breaking in Pyrus pyrifolia

To identify genes related to endodormancy in Pyrus pyrifolia, 124 clones exhibiting differential expression at three stages of bud endodormancy in the Japanese pear (Pyrus pyrifolia Nakai) ‘Gold Nijisseiki’ were isolated using the GeneFishing PCR method. Among the clones, 30, 54, and 19 clones showed high expression during the induction period (IP), deepest period (DP), and breaking period (BP) of endodormancy, respectively. In addition, 21 clones were overexpressed during IP and BP. The basic local alignment search tool searches revealed that 13 of these highly expressed genes have been previously identified. Based on the results of real-time PCR analysis, we focused on 8 genes as potential candidate genes related to bud endodormancy. Expression of 2 genes decreased from IP to DP during endodormancy in ‘Gold Nijisseiki,’ but increased in ‘Hengshanli,’ a plant that enters endodormancy at a different period. These genes were highly homologous to those encoding auxin-responsive family protein and E3 ubiquitin ligase PUB14. Expression of tonoplast intrinsic protein 1 increased briefly before BP as well as after 24h of hydrogen cyanamide (HC) treatment. During BP, genes highly homologous to those encoding thaumatin-like protein and auxin influx carrier component exhibited decreased and increased expression, respectively. This was also observed following HC treatment. Genes identified in this study may play a role in regulating the induction or breaking of endodormancy in the vegetative buds of P. pyrifolia.

Cultivar and areal differences in the breaking period of bud endodormancy in pear plants

We investigated the occurrence of bud break in Japanese pear [Pyrus pyrifolia (Burm.f.) Nakai] cultivars and wild pear species to estimate the chilling requirement (CR) for breaking bud endodormancy. The leaf buds of the ‘Hosui’ and ‘Kosui’ cultivars showed a higher CR than their counterpart floral buds. Each CR values of the ‘Kosui’ and ‘Niitaka’ cultivars in three areas, namely Tottori (cold-winter area), Saga (moderate-winter area), and Kumamoto (warm-winter area), were completely dependent on the chilling accumulation in each cultivar and area. Among these areas, a chill unit (CU) value of 1566 was observed in Kumamoto in mid- or late February. The results suggest that pear cultivars showing less than 1500CU should be selected for commercial production in that specific area, south of Kumamoto. Among the Japanese pear cultivars observed, ‘Akizuki,’ ‘Natsusoyoka,’ ‘Ryougetsu,’ and ‘Shinkansen’ showed the lowest CR, whereas ‘Syuugyoku’ showed the highest. The CR of Japanese pears ranged from 800 to 1800CU. Among the examined wild pear plants, a bud break incidence of at least 60% was observed in 14 plants during the period from January 7 to February 4. Among these, P. calleryana (No. 12) showed the lowest CR and was thus identified as a useful rootstock for warm-winter regions.

シアナミド処理がニホンナシ主要品種の自発休眠打破および開花期に及ぼす影響

シアナミド処理がニホンナシ主要品種の自発休眠打破および開花期に及ぼす影響

Effects of hydrogen cyanamide on antioxidant enzymes’ activity, proline and polyamine contents during bud dormancy release in Superior Seedless grapevine buds

The effect of hydrogen cyanamide (HC) on dormancy release, antioxidant enzyme’s activity and proline and free polyamine contents were investigated in ‘Superior Seedless’ grapevine buds. HC application caused a sharp decrease of catalase (CAT, EC 1.11.1.6) activity and a transient stimulation during the 5 days following treatment of peroxidase (POD, EC 1.11.1.7) and ascorbate peroxidase (APX, EC 1.11.1.11) activities. This coincided with an accumulation of total free polyamines, especially putrescine (Put). Proline content increased dramatically. There was a strong correlation between APX and POD activities and total free PAs and Put contents implying a possible stimulating effect of the latter compounds on these enzymes. These observations indicate that HC triggers an oxidative stress leading to bud endodormancy release. Afterward, as budbreak started, we observed a rapid proline and Put degradation; this could be responsible for reactivation of growth. Indeed, the decline in Put to (Spd + Spm) ratio, reported here, may be considered as a reliable biochemical marker of bud growth resumption.

Functional and Expressional Analyses of PmDAM Genes Associated with Endodormancy in Japanese Apricot

Bud endodormancy in woody plants plays an important role in their perennial growth cycles. We previously identified a MADS box gene, DORMANCY-ASSOCIATED MADS box6 (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.

Expressional regulation of PpDAM5 and PpDAM6, peach (Prunus persica) dormancy-associated MADS-box genes, by low temperature and dormancy-breaking reagent treatment

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.

Comparative Analyses of Dormancy-associated MADS-box Genes, PpDAM5 and PpDAM6, in Low- and High-chill Peaches (Prunus persica L.)

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.