Dormancy Cycle Research Articles

Regulatory circuits involving bud dormancy factor PpeDAM6

DORMANCY-ASSOCIATED MADS-BOX (DAM) genes have recently emerged as key potential regulators of the dormancy cycle and climate adaptation in perennial species. Particularly, PpeDAM6 has been proposed to act as a major repressor of bud dormancy release and bud break in peach (Prunus persica). PpeDAM6 expression is downregulated concomitantly with the perception of a given genotype-dependent accumulation of winter chilling time, and the coincident enrichment in H3K27me3 chromatin modification at a specific genomic region. We have identified three peach BASIC PENTACYSTEINE PROTEINs (PpeBPCs) interacting with two GA-repeat motifs present in this H3K27me3-enriched region. Moreover, PpeBPC1 represses PpeDAM6 promoter activity by transient expression experiments. On the other hand, the heterologous overexpression of PpeDAM6 in European plum (Prunus domestica) alters plant vegetative growth, resulting in dwarf plants tending toward shoot meristem collapse. These alterations in vegetative growth of transgenic lines associate with impaired hormone homeostasis due to the modulation of genes involved in jasmonic acid, cytokinin, abscisic acid, and gibberellin pathways, and the downregulation of shoot meristem factors, specifically in transgenic leaf and apical tissues. The expression of many of these genes is also modified in flower buds of peach concomitantly with PpeDAM6 downregulation, which suggests a role of hormone homeostasis mechanisms in PpeDAM6-dependent maintenance of floral bud dormancy and growth repression.

Unraveling the role of MADS transcription factor complexes in apple tree dormancy.

Summary A group of MADS transcription factors (TFs) are believed to control temperature‐mediated bud dormancy. These TFs, called DORMANCY‐ASSOCIATED MADS‐BOX (DAM), are encoded by genes similar to SHORT VEGETATIVE PHASE (SVP) from Arabidopsis. MADS proteins form transcriptional complexes whose combinatory composition defines their molecular function. However, how MADS multimeric complexes control the dormancy cycle in trees is unclear.Apple MdDAM and other dormancy‐related MADS proteins form complexes with MdSVPa, which is essential for the ability of transcriptional complexes to bind to DNA. Sequential DNA‐affinity purification sequencing (seq‐DAP‐seq) was performed to identify the genome‐wide binding sites of apple MADS TF complexes. Target genes associated with the binding sites were identified by combining seq‐DAP‐seq data with transcriptomics datasets obtained using a glucocorticoid receptor fusion system, and RNA‐seq data related to apple dormancy.We describe a gene regulatory network (GRN) formed by MdSVPa‐containing complexes, which regulate the dormancy cycle in response to environmental cues and hormonal signaling pathways. Additionally, novel molecular evidence regarding the evolutionary functional segregation between DAM and SVP proteins in the Rosaceae is presented.MdSVPa sequentially forms complexes with the MADS TFs that predominate at each dormancy phase, altering its DNA‐binding specificity and, therefore, the transcriptional regulation of its target genes.

Mobile forms of carbon in trees: metabolism and transport.

Plants constitute 80% of the biomass on earth, and almost two-thirds of this biomass is found in wood. Wood formation is a carbon (C)-demanding process and relies on C transport from photosynthetic tissues. Thus, understanding the transport process is of major interest for understanding terrestrial biomass formation. Here, we review the molecules and mechanisms used to transport and allocate C in trees. Sucrose is the major form in which C is transported in plants, and it is found in the phloem sap of all tree species investigated so far. However, in several tree species, sucrose is accompanied by other molecules, notably polyols and the raffinose family of oligosaccharides. We describe the molecules that constitute each of these transport groups, and their distribution across different tree species. Furthermore, we detail the metabolic reactions for their synthesis, the mechanisms by which trees load and unload these compounds in and out of the vascular system, and how they are radially transported in the trunk and finally catabolized during wood formation. We also address a particular C recirculation process between phloem and xylem that occurs in trees during the annual cycle of growth and dormancy. A search of possible evolutionary drivers behind the diversity of C-carrying molecules in trees reveals no consistent differences in C transport mechanisms between angiosperm and gymnosperm trees. Furthermore, the distribution of C forms across species suggests that climate-related environmental factors will not explain the diversity of C transport forms. However, the consideration of C-transport mechanisms in relation to tree–rhizosphere coevolution deserves further attention. To conclude the review, we identify possible future lines of research in this field.

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.

A quantitative analysis of primary dormancy and dormancy changes during burial in seeds of Brassica napus

For plants inhabiting unpredictable environments, scheduling germination can be challenging. Various responses to environmental conditions have been evolved by plants; these responses combine with variation in local climate to construct germination niche. Germination process may be regulated by a number of factors, among them, the type of seed dormancy and dormancy cycling play an important role in promoting survival after dispersal. In the present study, seeds of Brassica napus were tested for primary conditional dormancy (CD). Dormancy changes were quantified through seed population thermal germination parameters to test whether different genotypes of B. napus seeds (944, 966, Alestrom, Danube, Okanto and Rohan) are non‐dormant (ND) at the maturity or if they present primary dormancy (D or CD). In a burial experiment, B. napus seeds dormancy cycling in the natural soil seedbank was investigated. Germination of all genotypes decreased at 5 and > 20°C, showing narrower breadth of thermal niche for germination. Dormancy‐breaking treatments lead to the widening of thermal range permissive for germination. The lower limit (Tl(50)) and higher limit (Th(50)) temperatures for germination decreased and increased, respectively, for non‐dormant (after‐ripened seeds treated with GA3) seeds compared with fresh seeds in all genotypes. In fresh seeds, the Tl(50) and Th(50) for various genotypes ranged from 3.61 to 6.5°C and 25.0 to 29.0°C, respectively and ranged from 0.2 to 1.8°C and 35 to 41.0°C in non‐dormant seeds. Thus, fresh seeds of B. napus are dormant at dispersal and adopt delayed germination strategies to avoid summer drought. In the burial experiment, the results indicated that B. napus must have D/ND cycle in which fresh seeds first become dormant and then the cycle begins (CD→D↔CD↔ND), thus adopting both risk‐prone and risk‐adverse strategies to spread the likelihood of survival over time.

Global DNA methylation and cellular 5-methylcytosine and H4 acetylated patterns in primary and secondary dormant seeds of Capsella bursa-pastoris (L.) Medik. (shepherd\u2019s purse)

Despite the importance of dormancy and dormancy cycling for plants’ fitness and life cycle phenology, a comprehensive characterization of the global and cellular epigenetic patterns across space and time in different seed dormancy states is lacking. Using Capsella bursa-pastoris (L.) Medik. (shepherd’s purse) seeds with primary and secondary dormancy, we investigated the dynamics of global genomic DNA methylation and explored the spatio-temporal distribution of 5-methylcytosine (5-mC) and histone H4 acetylated (H4Ac) epigenetic marks. Seeds were imbibed at 30 °C in a light regime to maintain primary dormancy, or in darkness to induce secondary dormancy. An ELISA-based method was used to quantify DNA methylation, in relation to total genomic cytosines. Immunolocalization of 5-mC and H4Ac within whole seeds (i.e., including testa) was assessed with reference to embryo anatomy. Global DNA methylation levels were highest in prolonged (14 days) imbibed primary dormant seeds, with more 5-mC marked nuclei present only in specific parts of the seed (e.g., SAM and cotyledons). In secondary dormant seeds, global methylation levels and 5-mC signal where higher at 3 and 7 days than 1 or 14 days. With respect to acetylation, seeds had fewer H4Ac marked nuclei (e.g., SAM) in deeper dormant states, for both types of dormancy. However, the RAM still showed signal after 14 days of imbibition under dormancy-inducing conditions, suggesting a central role for the radicle/RAM in the response to perceived ambient changes and the adjustment of the seed dormancy state. Thus, we show that seed dormancy involves extensive cellular remodeling of DNA methylation and H4 acetylation.

Abstract 3161: The perlecan-semaphorin3A-plexinA1-neuropilin-1 Complex: Toggle control of prostate cancer cycles of dormancy and reactivation

Abstract Introduction: Metastatic prostate cancer (PCa) undergoes cycles of dormancy and reactivation, resulting in secondary metastasis, and leading to lethal disease. PCa preferentially metastasizes to bone where it can remain dormant for years after initial colonization. Previous work showed different growth and dormancy phenotypes in PCa tumors injected subcutaneously and intrafemorally, though the exact source of the dormancy-inducing factors remains undefined. We identified a novel receptor complex, the Perlecan-Semaphorin3A-PlexinA1-Neuropilin-1 (PSPN) complex, that is modulated by context-specific endothelial cell populations. The overall goal of this project is to identify the role of endothelial cells in stabilizing and silencing metastatic behavior via the PSPN complex, it's downstream pathways, and it's turnover by matrix metalloproteinase 7/Matrilysin (MMP-7). Methods: Live/dead assays coupled with immunolabeling and molecular approaches were used to determine the molecular impact of secreted endothelial cell factors on PCa signaling and behavior through the PSPN Complex in 2.5D and 3D microtumor cultures. Reverse phase protein arrays (RPPA) provided an unbiased means to assess the downstream molecular events in 3D co-cultures of PCa and microvascular cells. Results: Intact perlecan (P) induced clustering via engagement of PSPN complex. Destruction of complex components by MMP-7 activated growth and migration. FOXM1 was activated downstream of PSPN complex cleavage and resulting destabilization, consistent with escape from dormancy. Secreted factors from endothelial cells induced dormancy and reduced FOXM1 activation. Immunolocalization data showed internalization of plexin A1 with immunostaining both at the PCa cell surface and perinuclear, consistent with dynamic turnover associated with activation of signaling after loss of the PSPN complex. Conclusion: Intact PSPN complex at the PCa cell surface favors a dormant state that is reversed by MMP7 cleavage. In the cohesive state (PSPN complex intact) FOXM1 is “off”, inhibiting the transcription of growth and metastasis promoting factors. Context-specific endothelial cell populations secrete PSPN complex stabilizing proteins, silence downstream signaling, and result in a dormant phenotype. We propose that the PSPN complex at metastatic sites such as bone acts as a molecular toggle that can maintain dormancy until the switch is “flipped” by MMP-7 allowing reactivation, dyscohesion and favoring growth and metastasis. Citation Format: Tristen V. Tellman, Lindsey K. Sablatura, Lissette A. Cruz, Sue-Hwa Lin, Leland W. Chung, Mary C. Farach-Carson. The perlecan-semaphorin3A-plexinA1-neuropilin-1 Complex: Toggle control of prostate cancer cycles of dormancy and reactivation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3161.

Ethylene-Mediated Modulation of Bud Phenology, Cold Hardiness, and Hormone Biosynthesis in Peach (Prunus persica).

Spring frosts exacerbated by global climate change have become a constant threat to temperate fruit production. Delaying the bloom date by plant growth regulators (PGRs) has been proposed as a practical frost avoidance strategy. Ethephon is an ethylene-releasing PGR found to delay bloom in several fruit species, yet its use is often coupled with harmful effects, limiting its applicability in commercial tree fruit production. Little information is available regarding the mechanisms by which ethephon influences blooming and bud dormancy. This study investigated the effects of fall-applied ethephon on bud phenology, cold hardiness, and hormonal balance throughout the bud dormancy cycle in peach. Our findings concluded that ethephon could alter several significant aspects of peach bud physiology, including accelerated leaf fall, extended chilling accumulation period, increased heat requirements, improved cold hardiness, and delayed bloom date. Ethephon effects on these traits were primarily dependent on its concentration and application timing, with a high concentration (500 ppm) and an early application timing (10% leaf fall) being the most effective. Endogenous ethylene levels were induced significantly in the buds when ethephon was applied at 10% versus 90% leaf fall, indicating that leaves are essential for ethephon uptake. The hormonal analysis of buds at regular intervals of chilling hours (CH) and growing degree hours (GDH) also indicated that ethephon might exert its effects through an abscisic acid (ABA)-independent way in dormant buds. Instead, our data signifies the role of jasmonic acid (JA) in mediating budburst and bloom in peach, which also appears to be influenced by ethephon treatment. Overall, this research presents a new perspective in interpreting horticultural traits in the light of biochemical and molecular data and sheds light on the potential role of JA in bud dormancy, which deserves further attention in future studies that aim at mitigating spring frosts.

Overexpression of a SOC1-Related Gene Promotes Bud Break in Ecodormant Poplars.

Perennial species in the boreal and temperate regions are subject to extreme annual variations in light and temperature. They precisely adapt to seasonal changes by synchronizing cycles of growth and dormancy with external cues. Annual dormancy–growth transitions and flowering involve factors that integrate environmental and endogenous signals. MADS-box transcription factors have been extensively described in the regulation of Arabidopsis flowering. However, their participation in annual dormancy–growth transitions in trees is minimal. In this study, we investigate the function of MADS12, a Populus tremula × alba SUPPRESSOR OF CONSTANS OVEREXPRESSION 1 (SOC1)-related gene. Our gene expression analysis reveals that MADS12 displays lower mRNA levels during the winter than during early spring and mid-spring. Moreover, MADS12 activation depends on the fulfillment of the chilling requirement. Hybrid poplars overexpressing MADS12 show no differences in growth cessation and bud set, while ecodormant plants display an early bud break, indicating that MADS12 overexpression promotes bud growth reactivation. Comparative expression analysis of available bud break-promoting genes reveals that MADS12 overexpression downregulates the GIBBERELLINS 2 OXIDASE 4 (GA2ox4), a gene involved in gibberellin catabolism. Moreover, the mid-winter to mid-spring RNAseq profiling indicates that MADS12 and GA2ox4 show antagonistic expression during bud dormancy release. Our results support MADS12 participation in the reactivation of shoot meristem growth during ecodormancy and link MADS12 activation and GA2ox4 downregulation within the temporal events that lead to poplar bud break.

Dormancy cycles in Aquilegia oxysepala Trautv. et Mey. (Ranunculaceae), a species with non-deep simple morphophysiological dormancy

Seed dormancy and the formation of a soil seed bank is important plant regeneration strategies, especially if the environment is unpredictable. The present research explores how environmental factors control seed dormancy release, and how seed dormancy is related to the soil seed bank and regeneration of the perennial Aquilegia oxysepala. The effects of incubation temperature, light, cold and warm stratification, gibberellic acid (GA3) along with the germination phenology of A. oxysepala in the field were used to determine the type of seed dormancy. Seasonal change of seed dormancy was determined by regularly exhuming buried seeds and incubating them in laboratory conditions. A. oxysepala seeds has underdeveloped (small) embryos along with physiological dormancy at dispersal. With the increased amounts of cold stratification, the germination of A. oxysepala increased gradually. GA3 served as a substitute for cold stratification. Breaking of physiological dormancy under natural temperatures in the field occurred in winter, while growth of embryos and germination of seeds occurred in early spring. Viable seeds that had not germinated in early spring were induced into secondary dormancy by high soil temperatures. A. oxysepala provides one of a few examples of dormancy cycling in seeds with morphophysiological dormancy. Freshly matured seeds of A. oxysepala seeds have non-deep simple morphophysiological dormancy. The annual dormancy–non-dormancy cycle maintains the coordination between timing of seedling emergence with favorable seasons, thus increasing the survival chances of seedlings in environments with seasonal changes.

Morphophysiological dormancy synchronizes timing of seed germination of two alpine species of Meconopsis on the Tibetan Plateau to beginning of growing season

Timing of seed germination is critical for seedling establishment and growth of the plant to maturity. Theoretically, then, germination of alpine species should be restricted to a period that ensures seedlings will reach a critical size during the short growing season for overwinter survival. We hypothesized that seeds of two alpine monocarpic perennials of Meconopsis germinate only at the beginning of the growing season in early spring and that dormancy synchronizes the timing of germination to this period. We tested the effects of light, temperature, cold stratification and GA3 on germination of Meconopsis integrifolia and M. racemosa in the laboratory and germination responses to temperature during two 2-year periods of seed buried at 4450 m a.s.l. on the Tibetan Plateau. Most fresh seeds of both species were dormant, and the embryo underdeveloped, indicating morphophysiological dormancy (MPD). GA3 promoted embryo growth and germination of seeds. Buried seeds exhibited an annual dormancy cycle. The physiological component of MPD was released gradually in the field during autumn and winter, resulting in embryo growth (release of morphological component of MPD) and germination just after snowmelt in spring. Embryos in seeds that did not germinate the first year remained underdeveloped until the second spring. Delay of seed burial from October until January (simulating a delay in time of seed dispersal) delayed germination for 1 year but did not change the germination season. Thus, our hypothesis that MPD restricts germination to the beginning of the growing season is supported.

Interactive Effects of Light Quality during Day Extension and Temperature on Bud Set, Bud Burst and PaFTL2, PaCOL1-2 and PaSOC1 Expression in Norway Spruce (Picea abies (L.) Karst.)

Light and temperature are crucial factors for the annual growth rhythm of tree seedlings of the boreal and temperate zone. Dormant, vegetative winter buds are formed under short days (SD) and altered light quality. In the conifer Norway spruce, expression of FTL2 increases and PaCOL1-2 and PaSOC1 decrease under light regimes, inducing bud set. Although temperature is known to modulate the timing of bud set, information about combined effects of light climate and temperature on bud phenology and gene expression is limited. We studied the interactive effects of temperature (18, 22/24 °C) and day extension with blue (B), red (R) or far-red (FR) light or different R:FR ratios compared to SD on growth–dormancy cycling and expression of FTL2, PaCOL1-2 and PaSOC1 in Norway spruce seedlings. Day-extension with B light and all treatments involving FR light sustained shoot elongation, with increased growth at higher temperature. The R light treatment resulted in delayed/prevented bud set compared to SD, with more delay/prevented bud set at 24 °C than 18 °C. This was associated with lower PaFTL2-transcript levels at 24 °C and more rapid subsequent bud burst. For the growth-sustaining treatments (long days, FR and B light), the PaFTL2-transcript levels were generally lower and those of PaCO1-2 and PaSOC1 higher compared with SD and R light. In conclusion, our results demonstrate more reduced/prevented bud set and faster bud burst with increased temperature under day extension with R light, indicating less deep dormancy than at lower temperature. Also, sustained shoot elongation under the B light treatment (27 µmol m−2 s−1) in contrast to the lower B light-irradiances tested previously (≤13 µmol m−2 s−1), demonstrates an irradiance-dependent effect of day extension with B light.

Cold acclimation and deacclimation in wild blueberry: Direct and indirect influence of environmental factors and non-structural carbohydrates

Through the annual cycle of plant growth and dormancy, the winter season leads to profound metabolic changes allowing plants to undergo cold acclimation. In boreal environments, winter conditions are changing rapidly and are likely to cause damage to commercial wild lowbush blueberry. In this study, we addressed the level of frost hardiness and determined the role of environmental factors and nonstructural carbohydrates (NSCs) on frost hardiness. From autumn to spring, stem sections of Vaccinium angustifolium and Vaccinium myrtilloides were harvested each month in a commercial blueberry field to assess the relative electrolyte leakage and calculate the temperature at which 50% of the cells are lysed [LT50 ( °C)], used as frost hardiness index. Stems were also collected to assess soluble carbohydrates and starch. Correlations, principal component analysis (PCA) and structural equation modeling (SEM) were used to determine how environmental factors and NSCs directly or indirectly influence the frost hardiness index. Frost hardiness reached its lowest level in December and January with LT50 dropping below -60 °C. Seasonality of frost hardening was closely linked to photoperiod and temperature, generating clock-wise hysteretic loops that divide frost hardening into acclimation, from September to January, and deacclimation, from January to the end of May. Environmental factors such as photoperiod and temperature were more important in determining the level of frost hardiness during acclimation, with either direct or indirect effect through an influence on starch degradation, increasing soluble carbohydrate content. During deacclimation, soluble carbohydrates, especially raffinose, further induced a stronger direct regulation of frost hardiness. Direct biological regulation through raffinose defined the level of frost hardiness during deacclimation. However, the negative influence of temperature on raffinose concentration could increase vulnerability to winter warming events.

Intra-population seed survival during burial on a mass basis

Survival during burial is dependent upon a seed's ability to resist pathogen pressure and physiological aging. Several studies support a positive interspecific relationship between seed survival in soil and seed coat thickness. Our research attempted to understand if a similar intraspecific relationship occurs in Rudbeckia mollis (Asteraceae) seeds of different mass. Seeds were collected in August 2016 and separated into light (383 ± 7 µg), intermediate (409 ± 8 µg), and heavy (447 ± 10 µg) mass classes. Pericarp thickness was measured on fresh sections of seeds from each class. Seeds were buried 25 cm deep in a non-irrigated wildflower plot and monitored for viability with a standard germination test over 24 months. Final germination percentage varied from 0 to 98% with an overall mean of 82 ± 30% among all mass classes. Germination percentage and germination rate correlated positively with soil temperature suggesting dormancy cycling that is consistent with non-deep physiological dormancy. There was no consistent relationship between the likelihood of germination and seed mass but heavy class seeds were more likely to be recovered intact following burial. Pericarp thickness ranged from 24.7–41.4 µm and there was a weak positive relationship with mass. This research suggests no short-term relationship between intra-population seed mass and viability loss during burial. However, thicker seed coats in higher mass seeds may confer greater resistance to pathogen pressure. This research is supportive of a positive intra-population relationship between survival in soil and seed coat thickness.

Application of Natural Resources Property Theory to Hidden Resources

The visualization of property and resources is a defining foundation of the construction and application of a property rights framework. When humans encounter resources they cannot see— or hidden resources—, they have difficulties imagining an appropriate property regime. These hidden resources include subsurface resources (oil and gas reservoirs, groundwater, pore space), biological resources (migration paths, plant and animal dormancy cycles), informal and unrecognized land titles, and extraplanetary resources (asteroid mining and water). As a result, we often apply an existing two-dimensional property framework from visible resources to three and four-dimensional hidden resources. This article argues that lacking the ability to see resources—resource blindness—directly impacts our ability to use, manage, and conserve them. Conversely, resource sight—the ability to see resources—can tremendously aid the development of an effective and efficient property rights framework. This article also contends that hidden resources are best governed when owners and users understand the resource’s scientific properties. And those properties are likewise better gathered when the natural resource is visible to the human eye. Finally, if resource sight cannot be acquired, this article proposes avoiding resource conflicts by creating small groups of local and knowledgeable community property owners to advise in the resource’s management and encourage cooperative development.

Type-B cytokinin response regulators link hormonal stimuli and molecular responses during the transition from endo- to ecodormancy in apple buds.

Cytokinin together with MdoBRR1, MdoBRR8 and MdoBRR10 genes participate in the downregulation of MdoDAM1, contributing to the transition from endo- to ecodormancy in apple buds. The final step of cytokinin (CK) signaling pathway culminates in the activation of type-B response regulators (BRRs), important transcriptional factors in the modulation of CK-responsive genes. In this study, we performed a genome-wide analysis aiming to identify apple BRR family members and understand their involvement in bud dormancy control. The investigation identified ten MdoBRR protein-coding genes. A higher expression of three MdoBRR (MdoBRR1, MdoBRR9 and MdoBRR10) was observed in dormant buds in comparison to other developmental stages. Interestingly, in ecodormant buds these three MdoBRR genes were upregulated in a CK-dependent manner. Transcription profiles, determined during dormancy cycle under field and artificially controlled conditions, revealed that MdoBRR1 and MdoBRR8 played important roles in the transition from endo- to ecodormancy, probably mediated by endogenous CK stimuli. The expression of MdoBRR7, MdoBRR9, and MdoBRR10 was induced in ecodormant buds exposed to warm temperatures, indicating a putative role in growth resumption after chilling requirement fulfillment. Contrasting expression patternsin vivo between MdoBRRs and MdoDAM1, an essential dormancy establishment regulator, were observed during dormancy cycle and in CK-treated buds. Thereafter, in vivo transactivation assays showed that CK stimuli combined with transient overexpression of MdoBRR1, MdoBRR8, and MdoBRR10 resulted in downregulation of the reporter gene gusA driven by the MdoDAM1 promoter. These pieces of evidences point to the integration of CK-triggered responses through MdoBRRs that are able to downregulate MdoDAM1, contributing to dormancy release in apple.

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.

Dormancy cycling is accompanied by changes in ABA sensitivity in Polygonum aviculare seeds.

Polygonum aviculare seeds show high levels of primary dormancy (PD). Low winter temperatures alleviate dormancy and high spring temperatures induce seeds into secondary dormancy (SD), naturally establishing stable seedbanks cycling through years. The objective of this work was to elucidate the mechanism(s) involved in PD expression and release, and in SD induction in these seeds, and the extent to which abscisic acid (ABA) and gibberellins (GAs) are part of these mechanisms. Quantification of endogenous ABA both prior to and during incubation, and sensitivity to ABA and GAs, were assessed in seeds with contrasting dormancy. Expression analysis was performed for candidate genes involved in hormone metabolism and signaling. It was found that endogenous ABA content does not explain either dormancy release or dormancy induction; moreover, it does not seem to play a role in dormancy maintenance. However, dormancy modifications were commonly accompanied by changes in ABA sensitivity. Concomitantly, induction into SD, but not PD, was characterized by a increased PaABI-5 and PaPYL transcription, and a rise in GA sensitivity as a possible counterbalance effect. These results suggest that dormancy cycling in this species is related to changes in embryo sensitivity to ABA; however, this sensitivity appears to be controlled by different molecular mechanisms in primary and secondary dormant seeds.

Environmental factors driving seed dormancy and germination in tropical ecosystems: A perspective from campo rupestre species

Campo rupestre is a mountain tropical landscape occurring in Brazil. It is considered one of the most biologically diverse ecosystems in the world and a major center of endemism. This review addresses the particularities and crucial roles that environmental signaling plays in germination, longevity, and dormancy cycles of seeds of tropical species from campo rupestre vegetation. It also addresses how microhabitats can influence the hormonal and biochemical control of seed germination, longevity and dormancy, as well as how the interaction between soil humidity and temperature can modulate the acquisition and overcoming of secondary dormancy, affecting dormancy cycles of important groups of campo rupestre species. The available data show that most species of campo rupestre produce small seeds that germinate in a wide range of temperatures, require light to germinate and are able to form long-term persistent soil seed banks. Special attention should be given to seeds of Velloziaceae, which germinate in the dark at high temperatures with germination mediated mainly by abscisic acid, and to seeds of Eriocaulaceae and Xyridaceae, which have cyclical dormancy in fine synchrony with the seasonality of campo rupestre. Seasonal water availability, along with temperature, has shown to play a critical role in annual dormancy cycles, with the dynamics of gibberellins and abscisic acid levels driving the acquisition of secondary dormancy. This information is essential for understanding interactions between seeds and the environment and will provide useful contributions to the conservation and maintenance of campo rupestre vegetation and the preservation of this unique ecosystem.

Seasonal germination responses of seeds in fruits of the cold desert shrub Zygophyllum xanthoxylon buried in the field

We hypothesized that seeds of the central Asian cold desert shrub Zygophyllum xanthoxylon exhibit dormancy cycling in nature, which would help ensure that germination occurs at a favorable time for seedling survival. Fresh mature fruits of Z. xanthoxylon were placed on the soil surface and buried at a depth of 3–5 cm in soil in a natural habitat in August 2015. At regular intervals until July 2017, fruits/seeds were taken to the laboratory and evaluated for viability and germination. Fresh seeds in fruits germinated to 22–62% over a range of temperatures. After 6 weeks in the field, seeds on the surface germinated to 72–99% and those in soil to 70–100%. From 12 to 98 weeks, seeds on and in soil germinated to 72–100% at low (15/5 and 20/10 °C) temperatures, but germination at high (25/25 and 30/15 °C) temperatures was higher in summer than in spring. Seeds in fruits on the soil surface had higher germination percentages than those in the soil, especially at high temperatures. Although about half the seeds were dormant at maturity, they became nondormant in the field during summer. There was a decrease in ability to germinate at high temperatures in spring, especially for seeds in buried fruits, which indicates conditional dormancy/nondormancy cycling. Lack of germination at high temperatures in spring would help delay germination until the onset of the summer rainy season in the desert. Burial of fruits in the soil enhances the formation of a short-lived persistent seed bank.