What is going on with the hormonal control of flowering in plants?

PmRGL2/PmFRL3-PmSVP Module Regulates Flowering Time in Japanese apricot (Prunus mume Sieb. et Zucc.)

Temperate fruit trees rely on environmental and endogenous signals to trigger dormancy release and flowering. However, the knowledge of DELLA protein PmRGL2, a Prunus mume homolog of REPRESSOR OF GA-Like 2 (RGL2), which serves as an important inhibitory factor in gibberellin (gibberellin acid [GA]) signalling, is limited related to on its regulatory effects on dormancy release and flowering. In our study, the protein-protein interaction assays showed an interaction between PmRGL2 and PmFRL3, a Prunus mume homolog of FRIGIDA-LIKE (FRL). The FRL protein regulates flowering induction by binding to chaperone proteins. To understand the transcriptional regulation of PmRGL2 in Prunus mume, in detail's we constructed a ChIP-Seq library at four key stages of flower bud development. Genome-wide analysis screened a MCM1-AGAMOUSDEFICIENS Serum Response Factor box (MADS box) protein for two SHORT VEGETATIVE PHASEs (SVPs). Genetic analysis showed that overexpressing PmSVP in Arabidopsis thaliana reduced the GA content and delayed flowering, whereas PmSVP-like overexpression increased the GA content and promoted flowering. Protein-DNA binding assays revealed that the PmRGL2/PmFRL3 protein complex promoted PmSVP transcription while repressing PmSVP-like transcription, which inhibited the flowering process. As chilling requirements increased, the PmFRL3 protein was degraded. ThePmRGL2/PmFRL3 protein complex is disrupted. With the increase in the GA content within the flower buds, the PmRGL2 protein was degraded in response to GA signalling, and the function of PmSVP-like was released. It dominated flowering, leading to this process in Prunus mume. Therefore, we propose a mechanism by which the PmRGL2/PmFRL3 protein complex responds to GA and low-temperature signalling to regulate PmSVP and PmSVP-like synergistically and thus Prunus mume flowering time.

Temporal transcriptome analysis reveals the two-phase action of florigens in rice flowering

Two florigen genes, Hd3a and RFT1, are essential for the floral transition in rice. To elucidate the early steps of the transcriptional dynamics during rice floral induction, we compared a set of temporal transcriptome data of SAM (shoot apical meristem)-region samples between the wild-type and a non-flowering line of the hd3a rft1 double mutant during a short-day (SD) treatment after growing under long-day conditions for 42 days, and identified 6,978 DEGs (differentially expressed genes). As expected, FUL-like MADS-box genes were induced just after 4 days SD treatment; meanwhile, SEP-type and AGL-type MADS-box genes were induced after 9 days of SD treatment. We here newly revealed that majority of rhythmic genes including major circadian clock genes were not affected by the florigen genes, implying normal circadian clock phasing at the SAM regions regardless of floral transitions. We found that around two thousands of genes were repressed by Hd3a and RFT1 genes at the SAM regions before the SD treatments and become derepressed and similar to WT expression levels in the double mutants according to the SD treatments. These clearly imply two distinct actions of florigen genes: one for repression of some developmental key genes during vegetative growth possibly by very low level of florigen expression and the other for floral induction by relatively high florigen expressions upon short-day inductions. This repression by low levels of florigens may serve as a maintenance system for vegetative growth before floral induction, which implies a novel role for florigen genes in rice.

Unraveling the Complexities of Flowering in Ornamental Plants: The Interplay of Genetics, Hormonal Networks, and Microbiome

In ornamental plants, one of the most complex life processes, i.e., flowering, is regulated by interaction between the microbiota, hormones, and genes. Flowering plays an integral role in overall development and is quintessential for reproduction. Considering its importance, this review explores the complex mechanisms that determine the induction of flowering, highlighting the relationship between hormonal and genetic networks as well as the growing significance of the microbiome. Important genes involved in genetic control include FT, SOC1, and LFY. These genes react to environmental stimuli like photoperiod and vernalization. Auxins, cytokinin, and gibberellins are only a few hormone pathways important for floral growth and timing. The importance of plant-microbe interactions has been emphasized by current research, which shows that the microbiome affects flowering through processes like hormone production and availability of food. A comprehensive understanding of flowering induction is possible by integrating results from microbiota, hormones, and genetics studies, which may improve the breeding and culture of ornamental plants. For researchers to understand the complexity of flowering in ornamental plants and develop unique breeding strategies and improved floral qualities, it is critical to use interdisciplinary approaches, as this comprehensive investigation demonstrates.

A review of the interaction mechanisms between jasmonic acid (JA) and various plant hormones, as well as the core regulatory role of MYC2

Jasmonic acid (JA), as a defensive plant hormone, can synergistically or antagonistically interact with common hormones such as gibberellin (GA), abscisic acid (ABA), indole-3-acetic hormone acid (IAA), and ethylene (ETH) during the plant growth process, as well as interact with hormones such as melatonin (MT), brassinolide (BR), and resveratrol to regulate plant growth and development processes such as metabolite synthesis, pest and disease defense, and organ growth. The core regulatory factor MYC2 of JA mainly mediates the signal transduction pathways of these hormone interactions by interacting with other genes or regulating transcription. This article reviews the mechanism of cross-talk between JA and hormones such as ABA, GA, and salicylic acid (SA), and discusses the role of MYC2 in hormone interactions.

TaFT-D1 positively regulates grain weight by acting as a coactivator of TaFDL2 in wheat

FLOWERING LOCUS T (FT), a multifunctional regulator in crops, modulates multiple key agronomic traits such as flowering time or heading date and plant height; however, its role in grain development regulation is unclear. Herein, through genome-wide association studies (GWAS), we identified TaFT-D1, which encodes a phosphatidylethanolamine-binding protein (PEBP), as a candidate gene for grain weight in wheat. A one-bp insertion/deletion (InDel) (G/-) in the third exon of TaFT-D1, resulting in different protein lengths, was significantly associated with grain weight. TaFT-D1 knockout via the CRISPR-Cas9 system reduced grain size and weight, and TaFT-D1 increased grain size by promoting cell proliferation and starch synthesis. Transcriptome analysis revealed a significant decrease in the expression of cell cycle- and starch synthesis-related genes, including TaNAC019-3A, TaSWEET15-like-7B, TaCYCD4;1 and TaCYCD3;2, in the taft-d1 knockout line. TaFT-D1 interacted with the bZIP transcription factor TaFDL2, and the tafdl2 mutant presented relatively small grains, suggesting that TaFDL2 is a positive regulator of grain size. Moreover, TaFDL2 bound to the promoters of downstream cell cycle- and starch synthesis-related genes, activating their expression, whereas TaFT-D1 increased this activation via TaFDL2. Interaction assays demonstrated that TaFT-D1, Ta14-3-3A and TaFDL2 formed a regulatory complex. Furthermore, the TaFT-D1(G) allele was significantly correlated with greater thousand-grain weight and earlier heading. This favourable allele has undergone strong positive selection during wheat breeding in China. Our findings provide novel insights into how TaFT-D1 regulates grain weight and highlight its potential application for yield improvement in wheat.

The Role of FT/TFL1 Clades and Their Hormonal Interactions to Modulate Plant Architecture and Flowering Time in Perennial Crops

Human nutrition is inherently associated with the cultivation of vegetables, grains, and fruits, underscoring the critical need to understand and manipulate the balance between vegetative and reproductive development in plants. Despite the vast diversity within the plant kingdom, these developmental processes share conserved and interconnected pathways among angiosperms, predominantly involving age, vernalization, gibberellin, temperature, photoperiod, and autonomous pathways. These pathways interact with environmental cues and orchestrate the transition from vegetative growth to reproductive stages. Related to this, there are two key genes belonging to the same Phosphatidylethanolamine-binding proteins family (PEBP), the FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1), which activate and repress the floral initiation, respectively, in different plant species. They compete for transcription factors such as FLOWERING LOCUS D (FD) and 14-3-3 to form floral activation complexes (FAC) and floral repression complexes (FRC). The FT/TFL1 mechanism plays a pivotal role in meristem differentiation, determining developmental outcomes as determinate or indeterminate. This review aims to explore the roles of FT and TFL1 in plant architecture and floral induction of annual and perennial species, together with their interactions with plant hormones. In this context, we propose that plant development can be modulated by the response of FT and/or TFL1 to plant growth regulators (PGRs), which emerge as potential tools for mitigating the adverse effects of environmental changes on plant reproductive processes. Thus, understanding these mechanisms is crucial to address the challenges of agricultural practices, especially in the face of climate change.

Genetic engineering of RuBisCO by multiplex CRISPR editing small subunits in rice

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is required for photosynthetic carbon assimilation, as it catalyses the conversion of inorganic carbon into organic carbon. Despite its importance, RuBisCO is inefficient; it has a low catalytic rate and poor substrate specificity. Improving the catalytic performance of RuBisCO is one of the key routes for enhancing plant photosynthesis. As the basic subunit of RuBisCO, RbcS affects the catalytic properties and plays a key role in stabilizing the structure of holoenzyme. Yet, the understanding of functions of RbcS in crops is still largely unknown. Toward this end, we employed CRISPR-Cas9 technology to randomly edit five rbcS genes in rice (OsrbcS1-5), generating a series of knockout mutants. The mutations of predominant rbcS genes in rice photosynthetic tissues, OsrbcS2-5, conferred inhibited growth, delayed heading and reduced yield in the field conditions, accompanying with lower RuBisCO contents and activities and significantly reduced photosynthetic efficiency. The retarded phenotypes were severer caused by multiple mutations. In addition, we revealed that these mutants had fewer chloroplasts and starch grains and a lower sugar content in the shoot base, resulting in fewer rice tillers. Further structural analysis of the mutated RuBisCO enzyme in one rbcs2,3,5 mutant line uncovered no significant differences from the wild-type protein, indicating that the mutations of rbcS did not compromise the protein assembly or the structure. Our findings generated a mutant pool with genetic diversities, which offers a valuable resource and novel insights into unravelling the mechanisms of RuBisCO in rice. The multiplex genetic engineering approach of this study provides an effective and feasible strategy for RuBisCO modification in crops, further facilitate the photosynthesis improvement and sustainable crop production.

Transcriptome Analysis Reveals Sugar and Hormone Signaling Pathways Mediating Flower Induction in Pitaya (Hylocereus polyrhizus)

Flower induction in pitaya (Hylocereus polyrhizus) is regulated by complex gene networks involving multiple signaling pathways that ensure flower bud (FB) formation, but its molecular determinants remain largely unknown. In this study, we aimed to identify key genes and pathways involved in pitaya flower induction by analyzing transcriptomics profiles from differentiating buds. Our results indicate that the flower induction process is driven by a combination of sugar, hormone, transcription factor (TF), and flowering-related genes. We found that during the FB induction period, the levels of sugar, starch, auxin (AUX), cytokinin (CTK) active forms dihydrozeatin riboside (dhZR), zeatin riboside (ZR), N6-isopentenyladenosine (iPA), and brassinosteroid (BR) increase in the late stage (LS), while active gibberellins (GA3, GA4) decrease, signaling a metabolic and hormonal shift essential for flowering. Differential gene expression analysis identified key genes involved in starch and sugar metabolism, AUX, CTK, BR synthesis, and (GA) degradation, with notable differential expression in photoperiod (COL, CDF, TCP), age-related (SPL), and key flowering pathways (FT, FTIP, AGL, SOC1). This study reveals a multidimensional regulatory network for FB formation in pitaya, primarily mediated by the crosstalk between sugar and hormone signaling pathways, providing new insights into the molecular mechanism of FB formation in pitaya.

Untargeted metabolomics and functional analyses reveal that the secondary metabolite quinic acid associates with Angelica sinensis flowering

Flowering is a critical step in the plant life cycle. Angelica sinensis (Oliv.) Diels is a medicinal crop whose root is a well-known herbal medicine used in Asia. Early flowering causes changes in secondary metabolic flow and results in the loss of medicinal quality. Based on untargeted metabolomics studies, quinic acid was identified as a metabolite present in significantly higher concentrations during the early-flowering stage in A. sinensis leaves. This metabolite was subsequently investigated as a potential marker for early bolting in A. sinensis under field conditions. Moreover, quinic acid was found to accelerate flowering in the model plant Arabidopsis thaliana. Importantly, the flowering time was delayed in the quinate dehydrogenase At mutant, and this delay was reversed by quinic acid. Quinic acid upregulated the expression of the GA20OX and GID1 receptors and downregulated the expression of the inhibitor DELLA, thereby affecting the levels of FT and LFY and accelerating plant flowering. Quinic acid also significantly changed the expression of genes such as LOX, JAZ1, MYC2 and MYC3 in the jasmonic acid pathway. The trends of GID1, DELLA (GAI) and LOX2 protein expression were essentially consistent with those at the transcription level. These results suggest that quinic acid may promote plant flowering primarily by regulating the expression of genes and proteins in the gibberellin and jasmonic acid pathways.

Biological macromolecules mediated by environmental signals affect flowering regulation in plants: A comprehensive review

Flowering time is a crucial developmental stage in the life cycle of plants, as it determines the reproductive success and overall fitness of the organism. The precise regulation of flowering time is influenced by various internal and external factors, including genetic, environmental, and hormonal cues. This review provided a comprehensive overview of the molecular mechanisms and regulatory pathways of biological macromolecules (e.g. proteins and phytohormone) and environmental factors (e.g. light and temperature) involved in the control of flowering time in plants. We discussed the key proteins and signaling pathways that govern the transition from vegetative growth to reproductive development, highlighting the intricate interplay between genetic networks, environmental cues, and phytohormone signaling. Additionally, we explored the impact of flowering time regulation on plant adaptation, crop productivity, and agricultural practices. Moreover, we summarized the similarities and differences of flowering mechanisms between annual and perennial plants. Understanding the mechanisms underlying flowering time control is not only essential for fundamental plant biology research but also holds great potential for crop improvement and sustainable agriculture.

Morphological and physiological investigations reveal the regulatory effect of exogenous paclobutrazol on flowering promotion by winter warming in Chaenomeles speciosa 'Changshouguan'

The application of exogenous paclobutrazol (PP333) can improve the ability of winter warming to promote flowering in Chaenomeles speciosa, but the underlying mechanism is unclear. In this study, the cultivar 'Changshouguan' was sprayed with different concentrations of PP333 during flower bud differentiation, and the changes in the anatomical structures and physiological characteristics of the flower buds during the differentiation process, as well as the growth state of the flower buds and the effect on flowering promotion after winter warming treatment, were comprehensively investigated. The results showed that different concentrations of PP333 could advance the flowering time of 'Changshouguan' by 15-24 d under the warming treatment and increase the flowering duration to 17 d compared with those under the warming treatment alone (CK), and 1000 mg/L was the best treatment. Compared with the CK treatment, the PP333 treatment decreased the contents of indole acetic acid (IAA) and gibberellic acid (GAs) and increased the contents of zeatin ribosides (ZRs) and abscisic acid (ABA), thus changing the balance of hormones during flower bud differentiation. The inflection point (low point) of the curve shapes of the ZRs/GAs and ZRs/IAA ratios appeared significantly earlier, which showed a pattern consistent with soluble sugar and protein content and antioxidant activity. Interestingly, the above changes also corresponded to earlier flowering times during the warming process. Taken together, these results indicate that spraying an appropriate concentration of PP333 in the early stage of 'Changshouguan' flower bud differentiation promotes the early differentiation of flower buds and early flowering under winter warming treatment by altering their endogenous hormone content and homeostasis and changing their physiological state. The key to maintaining a relatively long flowering period in plants in the PP333 treatment group after flowering promotion was the increased accumulation of sugars and proteins.

Genetic and epigenetic basis of phytohormonal control of floral transition in plants

The timing of the developmental transition from the vegetative to the reproductive stage is critical for angiosperms, and is fine-tuned by the integration of endogenous factors and external environmental cues to ensure successful reproduction. Plants have evolved sophisticated mechanisms to response to diverse environmental or stress signals, and these can be mediated by hormones to coordinate flowering time. Phytohormones such as gibberellin, auxin, cytokinin, jasmonate, abscisic acid, ethylene, and brassinosteroids and the cross-talk among them are critical for the precise regulation of flowering time. Recent studies of the model flowering plant Arabidopsis have revealed that diverse transcription factors and epigenetic regulators play key roles in relation to the phytohormones that regulate floral transition. This review aims to summarize our current knowledge of the genetic and epigenetic mechanisms that underlie the phytohormonal control of floral transition in Arabidopsis, offering insights into how these processes are regulated and their implications for plant biology.

OsCOL5 suppresses heading through modulation of Ghd7 and Ehd2, enhancing rice yield

KEY MESSAGE

OsCOL5, an ortholog of Arabidopsis COL5, is involved in photoperiodic flowering and enhances rice yield through modulation of Ghd7 and Ehd2 and interactions with OsELF3-1 and OsELF3-2. Heading date, also known as flowering time, plays a crucial role in determining the adaptability and yield potential of rice (Oryza sativa L.). CONSTANS (CO)-like is one of the most critical flowering-associated gene families, members of which are evolutionarily conserved. Here, we report the molecular functional characterization of OsCOL5, an ortholog of Arabidopsis COL5, which is involved in photoperiodic flowering and influences rice yield. Structural analysis revealed that OsCOL5 is a typical member of CO-like family, containing two B-box domains and one CCT domain. Rice plants overexpressing OsCOL5 showed delayed heading and increases in plant height, main spike number, total grain number per plant, and yield per plant under both long-day (LD) and short-day (SD) conditions. Gene expression analysis indicated that OsCOL5 was primarily expressed in the leaves and stems with a diurnal rhythm expression pattern. RT-qPCR analysis of heading date genes showed that OsCOL5 suppressed flowering by up-regulating Ghd7 and down-regulating Ehd2, consequently reducing the expression of Ehd1, Hd3a, RFT1, OsMADS14, and OsMADS15. Yeast two-hybrid experiments showed direct interactions of OsCOL5 with OsELF3-1 and OsELF3-2. Further verification showed specific interactions between the zinc finger/B-box domain of OsCOL5 and the middle region of OsELF3-1 and OsELF3-2. Yeast one-hybrid assays revealed that OsCOL5 may bind to the CCACA motif. The results suggest that OsCOL5 functions as a floral repressor, playing a vital role in rice's photoperiodic flowering regulation. This gene shows potential in breeding programs aimed at improving rice yield by influencing the timing of flowering, which directly impacts crop productivity.

Integrated analysis of miRNAs, transcriptome and phytohormones in the flowering time regulatory network of tea oil camellia

Camellia oleifera is a crucial cash crop in the southern region of China. Timely flowering is a crucial characteristic for maximizing crop productivity. Nevertheless, the cold temperature and wet weather throughout the fall and winter seasons in South China impact the timing of flowering and the yield produced by C. oleifera. This study examined the miRNAs, transcriptomes, and phytohormones that are part of the flowering time regulatory networks in distinct varieties of C. oleifera (Sep, Oct, and Nov). This study provides evidence that phytohormones significantly impact the timing of flowering in C. oleifera leaves. There is a positive correlation between the accumulation variations of zeatin (cZ), brassinolide (BL), salicylic acid (SA), 1-amino cyclopropane carboxylic acid (ACC), and jasmonic acid (JA) and flowering time. This means that blooming occurs earlier when the quantity of these substances in leaves increases. Abscisic acid (ABA), trans-zeatin-riboside (tZR), dihydrozeatin (dh-Z), and IP (N6-Isopentenyladenine) exhibit contrasting effects. Furthermore, both miR156 and miR172 play a crucial function in regulating flowering time in C. oleifera leaves by modulating the expression of SOC1, primarily through the miR156-SPL and miR172-AP2 pathways. These findings establish a strong basis for future research endeavors focused on examining the molecular network associated with the flowering period of C. oleifera and controlling flowering time management through external treatments.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01473-2.

ACC SYNTHASE4 inhibits gibberellin biosynthesis and FLOWERING LOCUS T expression during citrus flowering

Flowering is an essential process in fruit trees. Flower number and timing have a substantial impact on the yield and maturity of fruit. Ethylene and gibberellin (GA) play vital roles in flowering, but the mechanism of coordinated regulation of flowering in woody plants by GA and ethylene is still unclear. In this study, a lemon (Citrus limon L. Burm) 1-aminocyclopropane-1-carboxylic acid synthase gene (CiACS4) was overexpressed in Nicotiana tabacum and resulted in late flowering and increased flower number. Further transformation of citrus revealed that ethylene and starch content increased, and soluble sugar content decreased in 35S:CiACS4 lemon. Inhibition of CiACS4 in lemon resulted in effects opposite to that of 35S:CiACS4 in transgenic plants. Overexpression of the CiACS4-interacting protein ETHYLENE RESPONSE FACTOR3 (CiERF3) in N. tabacum resulted in delayed flowering and more flowers. Further experiments revealed that the CiACS4-CiERF3 complex can bind the promoters of FLOWERING LOCUS T (CiFT) and GOLDEN2-LIKE (CiFE) and suppress their expression. Moreover, overexpression of CiFE in N. tabacum led to early flowering and decreased flowers, and ethylene, starch, and soluble sugar contents were opposite to those in 35S:CiACS4 transgenic plants. Interestingly, CiFE also bound the promoter of CiFT. Additionally, GA3 and 1-aminocyclopropanecarboxylic acid (ACC) treatments delayed flowering in adult citrus, and treatment with GA and ethylene inhibitors increased flower number. ACC treatment also inhibited the expression of CiFT and CiFE. This study provides a theoretical basis for the application of ethylene to regulate flower number and mitigate the impacts of extreme weather on citrus yield due to delayed flowering.

Identification of a Rye Spring Mutant Derived from a Winter Rye Variety by High-Altitude Environment Screening Using RNA Sequencing Technology

Wintergrazer-70 and Ganyin No1 are high-yield forage varieties suitable for cultivation in high-altitude areas of Tibet (4300 m above sea level). Ganyin No1 was developed from Wintergrazer-70, with the latter serving as its parent variety. Ganyin No1 was identified as a spring variety, and subsequent RNA sequencing was conducted. RNA sequencing analysis identified 4 differentially expressed genes related to vernalization and 28 genes related to photoperiod regulation. The Sc7296g5-i1G3 gene is related to the flowering inhibition of rye, which may be related to the phenotypic difference in the Ganyin No1 variety in winter and spring. This finding provides valuable insights for future research on Ganyin No1, especially in addressing feed shortages in Tibet during winter and spring.

The Function of Florigen in the Vegetative-to-Reproductive Phase Transition in and around the Shoot Apical Meristem

Plants undergo a series of developmental phases throughout their life-cycle, each characterized by specific processes. Three critical features distinguish these phases: the arrangement of primordia (phyllotaxis), the timing of their differentiation (plastochron) and the characteristics of the lateral organs and axillary meristems. Identifying the unique molecular features of each phase, determining the molecular triggers that cause transitions and understanding the molecular mechanisms underlying these transitions are keys to gleaning a complete understanding of plant development. During the vegetative phase, the shoot apical meristem (SAM) facilitates continuous leaf and stem formation, with leaf development as the hallmark. The transition to the reproductive phase induces significant changes in these processes, driven mainly by the protein FT (FLOWERING LOCUS T) in Arabidopsis and proteins encoded by FT orthologs, which are specified as 'florigen'. These proteins are synthesized in leaves and transported to the SAM, and act as the primary flowering signal, although its impact varies among species. Within the SAM, florigen integrates with other signals, culminating in developmental changes. This review explores the central question of how florigen induces developmental phase transition in the SAM. Future research may combine phase transition studies, potentially revealing the florigen-induced developmental phase transition in the SAM.

The tomato EAR-motif repressor, SlERF36, accelerates growth transitions and reduces plant life cycle by regulating GA levels and responses

Faster vegetative growth and early maturity/harvest reduce plant life cycle time and are important agricultural traits facilitating early crop rotation. GA is a key hormone governing developmental transitions that determine growth speed in plants. An EAR-motif repressor, SlERF36 that regulates various growth transitions, partly through regulation of the GA pathway and GA levels, was identified in tomato. Suppression of SlERF36 delayed germination, slowed down organ growth and delayed the onset of flowering time, fruit harvest and whole-plant senescence by 10-15 days. Its over-expression promoted faster growth by accelerating all these transitions besides increasing organ expansion and plant height substantially. The plant life cycle and fruit harvest were completed 20-30 days earlier than control without affecting yield, in glasshouse as well as net-house conditions, across seasons and generations. These changes in life cycle were associated with reciprocal changes in expression of GA pathway genes and basal GA levels between suppression and over-expression lines. SlERF36 interacted with the promoters of two GA2 oxidase genes, SlGA2ox3 and SlGA2ox4, and the DELLA gene, SlDELLA, reducing their transcription and causing a 3-5-fold increase in basal GA3/GA4 levels. Its suppression increased SlGA2ox3/4 transcript levels and reduced GA3/GA4 levels by 30%-50%. SlERF36 is conserved across families making it an important candidate in agricultural and horticultural crops for manipulation of plant growth and developmental transitions to reduce life cycles for faster harvest.

Effect of heterologous expression of FT gene from Medicago truncatula in growth and flowering behavior of olive plants

Olive (Olea europaea L. subsp. europaea) is one of the most important crops of the Mediterranean Basin and temperate areas worldwide. Obtaining new olive varieties adapted to climatic changing conditions and to modern agricultural practices, as well as other traits such as biotic and abiotic stress resistance and increased oil quality, is currently required; however, the long juvenile phase, as in most woody plants, is the bottleneck in olive breeding programs. Overexpression of genes encoding the 'florigen' Flowering Locus T (FT), can cause the loss of the juvenile phase in many perennials including olives. In this investigation, further characterization of three transgenic olive lines containing an FT encoding gene from Medicago truncatula, MtFTa1, under the 35S CaMV promoter, was carried out. While all three lines flowered under in vitro conditions, one of the lines stopped flowering after acclimatisation. In soil, all three lines exhibited a modified plant architecture; e.g., a continuous branching behaviour and a dwarfing growth habit. Gene expression and hormone content in shoot tips, containing the meristems from which this phenotype emerged, were examined. Higher levels of OeTFL1, a gene encoding the flowering repressor TERMINAL FLOWER 1, correlated with lack of flowering. The branching phenotype correlated with higher content of salicylic acid, indole-3-acetic acid and isopentenyl adenosine, and lower content of abscisic acid. The results obtained confirm that heterologous expression of MtFTa1 in olive induced continuous flowering independently of environmental factors, but also modified plant architecture. These phenotypical changes could be related to the altered hormonal content in transgenic plants.

Regulatory frameworks involved in the floral induction, formation and developmental programming of woody horticultural plants: a case study on blueberries

Flowering represents a crucial stage in the life cycles of plants. Ensuring strong and consistent flowering is vital for maintaining crop production amidst the challenges presented by climate change. In this review, we summarized key recent efforts aimed at unraveling the complexities of plant flowering through genetic, genomic, physiological, and biochemical studies in woody species, with a special focus on the genetic control of floral initiation and activation in woody horticultural species. Key topics covered in the review include major flowering pathway genes in deciduous woody plants, regulation of the phase transition from juvenile to adult stage, the roles of CONSTANS (CO) and CO-like gene and FLOWERING LOCUS T genes in flower induction, the floral regulatory role of GA-DELLA pathway, and the multifunctional roles of MADS-box genes in flowering and dormancy release triggered by chilling. Based on our own research work in blueberries, we highlighted the central roles played by two key flowering pathway genes, FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1, which regulate floral initiation and activation (dormancy release), respectively. Collectively, our survey shows both the conserved and diverse aspects of the flowering pathway in annual and woody plants, providing insights into the potential molecular mechanisms governing woody plants. This paves the way for enhancing the resilience and productivity of fruit-bearing crops in the face of changing climatic conditions, all through the perspective of genetic interventions.

Unlocking Nature's Clock: CRISPR Technology in Flowering Time Engineering

Flowering is a crucial process in the life cycle of most plants as it is essential for the reproductive success and genetic diversity of the species. There are situations in which breeders want to expedite, delay, or prevent flowering, for example, to shorten or prolong vegetative growth, to prevent unwanted pollination, to reduce the risk of diseases or pests, or to modify the plant's phenotypes. This review aims to provide an overview of the current state of knowledge to use CRISPR/Cas9, a powerful genome-editing technology to modify specific DNA sequences related to flowering induction. We discuss the underlying molecular mechanisms governing the regulation of the photoperiod, autonomous, vernalization, hormonal, sugar, aging, and temperature signal pathways regulating the flowering time. In addition, we are investigating the most effective strategies for nominating target genes. Furthermore, we have collected a dataset showing successful applications of CRISPR technology to accelerate flowering in several plant species from 2015 up to date. Finally, we explore the opportunities and challenges of using the potential of CRISPR technology in flowering time engineering.

Transcriptomic response for revealing the molecular mechanism of oat flowering under different photoperiods

Proper flowering is essential for the reproduction of all kinds of plants. Oat is an important cereal and forage crop; however, its cultivation is limited because it is a long-day plant. The molecular mechanism by which oats respond to different photoperiods is still unclear. In this study, oat plants were treated under long-day and short-day photoperiods for 10 days, 15 days, 20 days, 25 days, 30 days, 40 days and 50 days, respectively. Under the long-day treatment, oats entered the reproductive stage, while oats remained vegetative under the short-day treatment. Forty-two samples were subjected to RNA-Seq to compare the gene expression patterns of oat under long- and short-day photoperiods. A total of 634-5,974 differentially expressed genes (DEGs) were identified for each time point, while the floral organ primordium differentiation stage showed the largest number of DEGs, and the spikelet differentiation stage showed the smallest number. Gene Ontology (GO) analysis showed that the plant hormone signaling transduction and hormone metabolism processes significantly changed in the photoperiod regulation of flowering time in oat. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Mapman analysis revealed that the DEGs were mainly concentrated in the circadian rhythm, protein antenna pathways and sucrose metabolism process. Additionally, transcription factors (TFs) involved in various flowering pathways were explored. Combining all this information, we established a molecular model of oat flowering induced by a long-day photoperiod. Taken together, the long-day photoperiod has a large effect at both the morphological and transcriptomic levels, and these responses ultimately promote flowering in oat. Our findings expand the understanding of oat as a long-day plant, and the explored genes could be used in molecular breeding to help break its cultivation limitations in the future.

Deciphering aroma formation during flowering in nectar tree (Tilia amurensis): insights from integrated metabolome and transcriptome analysis

Tilia amurensis is a significant ornamental and economically-important tree species, known for its fragrant flowers, which are a source of high-quality honey production. However, the regulatory mechanisms involved in aroma formation during flower development in T. amurensis remains limited. The current study revealed the detection of plant hormones at every assessed stage of flower development. Among them, auxin and brassinosteroid contents significantly increased at stage 3, potentially regulating crucial functions during T. amurensis flower development. Moreover, the study examined the levels and change patterns of secondary metabolites and employed a combination of transcriptomics and metabolomics to comprehensively assess essential structural genes implicated in the biosynthesis pathways of terpenoid and phenylpropanoid. A comprehensive set of 89,526 differentially expressed genes (DEGs) was uncovered, including candidate structural genes ACAT, HDS, TPS, 4CL, CAD, and CCOAMT, which are specifically involved in the biosynthesis of terpenoids and phenylpropanoids. Maslinic acid, 2α,3α-dihydroxyursolic acid, and betulinic acid were accumulated in the terpenoid biosynthesis pathway. In contrast, metabolites with differential accumulation, such as phenylalanine, coniferyl alcohol, and cinnamic acid, were specifically enriched in the phenylpropanoid biosynthesis pathway. The C2H2, MYB, and NAC transcription factor families are crucially associated with the terpenoid and phenylpropanoid biosynthesis pathways. Two transcription factors, C2H2-17 and MYB-24, exhibited strong co-expression with structural genes in two networks, and were identified as central regulatory factors. These findings establish a solid groundwork for elucidating the generation of floral fragrance and provide comprehensive genetic and metabolic information for further studies on T. amurensis.

Flowering induction in cassava using photoperiod extension premature pruning and plant growth regulators

Cassava (Manihot esculenta Crantz) is a vital crop for food and economic security in many regions of the world. Despite the economic and social importance of cassava, challenges persist in developing superior varieties that meet the needs of farmers in terms of agronomic performance, nutritional quality, and resistance to pests and diseases. One of the main obstacles for genetic improvement is the lack of synchronization in flowering and the abortion of young flowers, making planned crosses and progeny production difficult. Therefore, the aim of this study was to evaluate the effect of photoperiod, premature pruning, and growth regulators on cassava flowering under low-altitude conditions in Brazil. Eight cassava clones with contrasting flowering capacity were assessed in Cruz das Almas, Bahia, using two photoperiods (ambient condition and extended photoperiod with red light for 12 hours), premature pruning at the first and second branching levels (with and without pruning), and the application of growth regulators: 0.5 mM 6-benzyladenine (BA) and 4.0 mM silver thiosulfate (STS) (with and without). Plots were assessed weekly for the number of female (NFF) and male (NMF) flowers, height of the first branching (H1B, in cm), number of days to the first branching (ND1B), and the number of branching events up to 240 days after planting (NOB). The extended photoperiod did not promote an increase in the number of flowers but allowed for precocity in cassava flowering, reducing the onset of flowering by up to 35 days, and significantly increasing the number of branches, which is closely related to flowering. The use of pruning and plant growth regulators (PGR) resulted in an increase in NFF from 2.2 (control) to 4.6 and NMF from 8.1 to 21.1 flowers. Therefore, under hot and humid tropical conditions at low altitudes in the Recôncavo of Bahia, manipulating the photoperiod and using premature pruning and plant growth regulators can accelerate cassava flowering, benefiting genetic improvement programs.

Transcriptome analysis during vernalization in wheat (Triticum aestivum L.)

BACKGROUND

Vernalization, as a vital process in the life cycle of winter cereal, has important effects on floral organ formation and flowering time. Many morphological changes together with molecular changes occur during the vernalization period. Here, we used transcriptome sequencing to analyze the transcriptomic changes in wheat leaves before, during and after vernalization using the winter wheat cultivar 'Shiluan02-1'.

RESULTS

A total of 16,370 differentially expressed genes were obtained across different vernalization periods. Gene Ontology enrichment analysis revealed that photoperiodism, photoprotection, photosynthesis, lipid transport and biosynthetic process, and chlorophyll metabolic process were closely related to vernalization. In addition, AP2/ERF, C2H2, bHLH, WRKY, MYB, MYB-related, and NAC transcription factors were significantly enriched during vernalization, and the transcription factor expression patterns suggested the intricate regulation of transcription factor modules in plant vernalization pathways. Analysis of gene expression patterns of the MADS-box transcription factor genes showed different expression patterns during vernalization phases, among which VERNALIZATION1 (VRN1) genes were found to gradually increase during vernalization periods from V0 to V35, while decline in the V42 phase, then increase after vernalization. The Tavrt-2 gene cooperated with Tavrn1 to regulate flowering induced by vernalization, and its expression level was rapidly increased by vernalization but declined in the V42 phase and then increased after vernalization. Some genes from the ICE-CBF-COR pathway were also identified, and additional analysis indicated that some key genes related to phytohormone biosynthesis and signal transduction were enriched during the vernalization period, such as gibberellic acid, ethylene, abscisic acid and jasmonic acid biosynthesis and signaling pathway genes.

CONCLUSIONS

Our study provides valuable molecular information for future studies on wheat vernalization regulation and also serves as an excellent reference for future wheat breeding.

ETHYLENE INSENSITIVE3/EIN3-LIKE1 modulate FLOWERING LOCUS C expression via histone demethylase interaction

Time to flowering (vegetative to reproductive phase) is tightly regulated by endogenous factors and environmental cues to ensure proper and successful reproduction. How endogenous factors coordinate with environmental signals to regulate flowering time in plants is unclear. Transcription factors ETHYLENE INSENSITIVE 3 (EIN3) and its homolog EIN3 LIKE 1 (EIL1) are the core downstream regulators in ethylene signal transduction, and their null mutants exhibit late flowering in Arabidopsis (Arabidopsis thaliana); however, the precise mechanism of floral transition remains unknown. Here, we reveal that FLOWERING LOCUS D (FLD), encoding a histone demethylase acting in the autonomous pathway of floral transition, physically associates with EIN3 and EIL1. Loss of EIN3 and EIL1 upregulated transcriptional expression of the floral repressor FLOWERING LOCUS C (FLC) and its homologs in Arabidopsis, and ethylene-insensitive mutants displayed inhibited flowering in an FLC-dependent manner. We further demonstrated that EIN3 and EIL1 directly bind to FLC loci, modulating their expression by recruiting FLD and thereafter removing di-methylation of lysine 4 on histone H3 (H3K4me2). In plants treated with 1-aminocyclopropane-1-carboxylic acid, decreased expression of FLD resulted in increased enrichment of H3K4me2 at FLC loci and transcriptional activation of FLC, leading to floral repression. Our study reveals the role of EIN3 and EIL1 in FLC-dependent and ethylene-induced floral repression and elucidates how phytohormone signals are transduced into chromatin-based transcriptional regulation.

Identification and promoter analysis of a GA-stimulated transcript 1 gene from Jatropha curcas

KEY MESSAGE

Overexpression of JcGAST1 promotes plant growth but inhibits pistil development. The pyrimidine box and CGTCA motif of the JcGAST1 promoter were responsible for the GA and MeJA responses. Members of the gibberellic acid-stimulated Arabidopsis (GASA) gene family play roles in plant growth and development, particularly in flower induction and seed development. However, there is still relatively limited knowledge of GASA genes in Jatropha curcas. Herein, we identified a GASA family gene from Jatropha curcas, namely, JcGAST1, which encodes a protein containing a conserved GASA domain. Sequence alignment showed that the JcGAST1 protein shares 76% sequence identity and 80% sequence similarity with SlGAST1. JcGAST1 had higher expression and protein levels in the female flowers than in the male flowers. Overexpression of JcGAST1 in tobacco promotes plant growth but inhibits pistil development. JcGAST1 expression was upregulated by GA and downregulated by MeJA. Promoter analysis indicated that the pyrimidine box and CGTCA motif were the GA- and MeJA-responsive elements of the JcGAST1 promoter. Using a Y1H screen, six transcription factors were found to interact with the pyrimidine box, and three transcription factors were found to interact with the CGTCA motif. Overall, the results of this study improve our understanding of the JcGAST1 gene and provide useful information for further studies.

Circular RNAs modulate the floral fate acquisition in soybean shoot apical meristem

BACKGROUND

Soybean (Glycine max), a major oilseed and protein source, requires a short-day photoperiod for floral induction. Though key transcription factors controlling flowering have been identified, the role of the non-coding genome is limited. Circular RNAs (circRNAs) recently emerged as a novel class of RNAs with critical regulatory functions. However, a study on circRNAs during the floral transition of a crop plant is lacking. We investigated the expression and potential function of circRNAs in floral fate acquisition by soybean shoot apical meristem in response to short-day treatment.

RESULTS

Using deep sequencing and in-silico analysis, we denoted 384 circRNAs, with 129 exhibiting short-day treatment-specific expression patterns. We also identified 38 circRNAs with predicted binding sites for miRNAs that could affect the expression of diverse downstream genes through the circRNA-miRNA-mRNA network. Notably, four different circRNAs with potential binding sites for an important microRNA module regulating developmental phase transition in plants, miR156 and miR172, were identified. We also identified circRNAs arising from hormonal signaling pathway genes, especially abscisic acid, and auxin, suggesting an intricate network leading to floral transition.

CONCLUSIONS

This study highlights the gene regulatory complexity during the vegetative to reproductive transition and paves the way to unlock floral transition in a crop plant.

Tomato sucrose transporter SlSUT4 participates in flowering regulation by modulating gibberellin biosynthesis

The functions of sucrose transporters (SUTs) differ among family members. The physiological function of SUT1 has been studied intensively, while that of SUT4 in various plant species including tomato (Solanum lycopersicum) is less well-understood. In this study, we characterized the function of tomato SlSUT4 in the regulation of flowering using a combination of molecular and physiological analyses. SlSUT4 displayed transport activity for sucrose when expressed in yeast (Saccharomyces cerevisiae), and it localized at both the plasma membrane and tonoplast. SlSUT4 interacted with SlSUT1, causing partial internalization of the latter, the main phloem loader of sucrose in tomato. Silencing of SlSUT4 promoted SlSUT1 localization to the plasma membrane, contributing to increased sucrose export and thus increased sucrose level in the shoot apex, which promoted flowering. Both silencing of SlSUT4 and spraying with sucrose suppressed gibberellin biosynthesis through repression of ent-kaurene oxidase and gibberellin 20-oxidase-1 (2 genes encoding key enzymes in gibberellin biosynthesis) expression by SlMYB76, which directly bound to their promoters. Silencing of SlMYB76 promoted gibberellin biosynthesis. Our results suggest that SlSUT4 is a functional SUT in tomato; downregulation of SlSUT4 expression enhances sucrose transport to the shoot apex, which promotes flowering by inhibiting gibberellin biosynthesis.

Hormonal control of promoter activities of Cannabis sativa prenyltransferase 1 and 4 and salicylic acid mediated regulation of cannabinoid biosynthesis

Cannabis sativa aromatic prenyltransferase 4 (CsPT4) and 1 (CsPT1) have been shown to catalyze cannabigerolic acid (CBGA) biosynthesis, a step that rate-limits the cannabinoid biosynthetic pathway; both genes are highly expressed in flowers. CsPT4 and CsPT1 promoter driven β-glucuronidase (GUS) activities were detected in leaves of cannabis seedlings, and strong CsPT4 promoter activities were associated with glandular trichomes. Hormonal regulation of cannabinoid biosynthetic genes is poorly understood. An in silico analysis of the promoters identified putative hormone responsive elements. Our work examines hormone-responsive elements in the promoters of CsPT4 and CsPT1 in the context of physiological responses of the pathway to the hormone in planta. Dual luciferase assays confirmed the regulation of promoter activities by the hormones. Further studies with salicylic acid (SA) demonstrated that SA pretreatment increased the expression of genes located downstream of the cannabinoid biosynthetic pathway. The results from all aspects of this study demonstrated an interaction between certain hormones and cannabinoid synthesis. The work provides information relevant to plant biology, as we present evidence demonstrating correlations between molecular mechanisms that regulate gene expression and influence plant chemotypes.

High ambient temperature impacts on flowering time in Brassica napus through both H2A.Z-dependent and independent mechanisms

Knowledge concerning the integration of genetic pathways mediating the responses to environmental cues controlling flowering initiation in crops is scarce. Here, we reveal the diversity in oilseed rape (OSR) flowering response to high ambient temperature. Using a set of different spring OSR varieties, we found a consistent flowering delay at elevated temperatures. Remarkably, one of the varieties assayed exhibited the opposite behaviour. Several FT-like paralogs are plausible candidates to be part of the florigen in OSR. We revealed that BnaFTA2 plays a major role in temperature-dependent flowering initiation. Analysis of the H2A.Z histone variant occupancy at this locus in different Brassica napus varieties produced contrasting results, suggesting the involvement of additional molecular mechanisms in BnaFTA2 repression at high ambient temperature. Moreover, BnARP6 RNAi plants showed little accumulation of H2A.Z at high temperature while maintaining temperature sensitivity and delayed flowering. Furthermore, we found that H3K4me3 present in BnaFTA2 under inductive flowering conditions is reduced at high temperature, suggesting a role for this hallmark of transcriptionally active chromatin in the OSR flowering response to warming. Our work emphasises the plasticity of flowering responses in B. napus and offers venues to optimise this process in crop species grown under suboptimal environmental conditions.

The hot science in rice research: How rice plants cope with heat stress

Global climate change has great impacts on plant growth and development, reducing crop productivity worldwide. Rice (Oryza sativa L.), one of the world's most important food crops, is susceptible to high-temperature stress from seedling stage to reproductive stage. In this review, we summarize recent advances in understanding the molecular mechanisms underlying heat stress responses in rice, including heat sensing and signalling, transcriptional regulation, transcript processing, protein translation, and post-translational regulation. We also highlight the irreversible effects of high temperature on reproduction and grain quality in rice. Finally, we discuss challenges and opportunities for future research on heat stress responses in rice.

Brassica rapa orphan gene BR1 delays flowering time in Arabidopsis

Orphan genes are essential to the emergence of species-specific traits and the process of evolution, lacking sequence similarity to any other identified genes. As they lack recognizable domains or functional motifs, however, efforts to characterize these orphan genes are often difficult. Flowering is a key trait in Brassica rapa, as premature bolting can have a pronounced adverse impact on plant quality and yield. Bolting resistance-related orphan genes, however, have yet to be characterized. In this study, an orphan gene designated BOLTING RESISTANCE 1 (BR1) was identified and found through gene structural variation analyses to be more highly conserved in Chinese cabbage than in other available accessions. The expression of BR1 was increased in bolting resistant Chinese cabbage and decreased in bolting non-resistant type, and the expression of some mark genes were consist with bolting resistance phenotype. BR1 is primarily expressed in leaves at the vegetative growth stage, and the highest BR1 expression levels during the flowering stage were observed in the flower buds and silique as compared to other tissue types. The overexpression of BR1 in Arabidopsis was associated with enhanced bolting resistance under long day (LD) conditions, with these transgenic plants exhibiting significant decreases in stem height, rosette radius, and chlorophyll content. Transcriptomic sequencing of WT and BR1OE plants showed the association of BR1 with other bolting resistance genes. Transcriptomic sequencing and qPCR revealed that six flowering integrator genes and one chlorophyll biosynthesis-related gene were downregulated following BR1 overexpression. Six key genes in photoperiodic flowering pathway exhibited downward expression trends in BR1OE plants, while the expression of floral repressor AtFLC gene was upregulated. The transcripts of these key genes were consistent with observed phenotypes in BR1OE plants, and the results indicated that BR1 may function through vernalization and photoperiodic pathway. Instead, the protein encoded by BR1 gene was subsequently found to localize to the nucleus. Taken together, we first propose that orphan gene BR1 functions as a novel regulator of flowering time, and these results suggested that BR1 may represent a promising candidate gene to support the selective breeding of Chinese cabbage cultivars with enhanced bolting resistance.

Recent advances and future perspectives in early-maturing cotton research

Cotton's fundamental requirements for long periods of growth and specific seasonal temperatures limit the global arable areas that can be utilized to cultivate cotton. This constraint can be alleviated by breeding for early-maturing varieties. By delaying the sowing dates without impacting the boll-opening time, early-maturing varieties not only mitigate the yield losses brought on by unfavorable weathers in early spring and late autumn but also help reducing the competition between cotton and other crops for arable land, thereby optimizing the cropping system. This review presents studies and breeding efforts for early-maturing cotton, which efficiently pyramid early maturity, high-quality, multiresistance traits, and suitable plant architecture by leveraging pleiotropic genes. Attempts are also made to summarize our current understanding of the molecular mechanisms underlying early maturation, which involves many pathways such as epigenetic, circadian clock, and hormone signaling pathways. Moreover, new avenues and effective measures are proposed for fine-scale breeding of early-maturing crops to ensure the healthy development of the agricultural industry.

BcOPR3 Mediates Defense Responses to Biotrophic and Necrotrophic Pathogens in Arabidopsis and Non-heading Chinese Cabbage

In plants, the salicylic acid (SA) and jasmonic acid (JA) signaling pathways usually mediate the defense response to biotrophic and necrotrophic pathogens, respectively. Our previous work showed that after non-heading Chinese cabbage (NHCC) was infected with the biotrophic pathogen Hyaloperonospora parasitica, expression of the JA biosynthetic gene BcOPR3 is induced; however, its molecular mechanism remains unclear. Here, we overexpressed BcOPR3 in Arabidopsis and silenced BcOPR3 in NHCC001 plants to study the defensive role of BcOPR3 in plants against pathogen invasion. The results showed that overexpression of BcOPR3 increased the susceptibility of Arabidopsis to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) but enhanced its resistance to Botrytis cinerea. BcOPR3-silenced NHCC001 plants with a 50% reduction in BcOPR3 expression increased their resistance to downy mildew by reducing the hyphal density and spores of H. parasitica. In addition, BcOPR3-partly silenced NHCC001 plants were also resistant to B. cinerea, which could be the result of a synergistic effect of JA and SA. These findings indicate a complicated role of BcOPR3 in the mediating defense responses to biotrophic and necrotrophic pathogens.

Identification of Differentially Expressed Genes Related to Floral Bud Differentiation and Flowering Time in Three Populations of Lycoris radiata

The transition from vegetative to reproductive growth is important for controlling the flowering of Lycoris radiata. However, the genetic control of this complex developmental process remains unclear. In this study, 18 shoot apical meristem (SAM) samples were collected from early-, mid- and late-flowering populations during floral bud differentiation. The histological analysis of paraffin sections showed that the floral bud differentiation could be divided into six stages; the differentiation time of the early group was earlier than that of the middle and late groups, and the late group was the latest. In different populations, some important differential genes affecting the flowering time were identified by transcriptome profiles of floral bud differentiation samples. Weighted gene co-expression network analysis (WGCNA) was performed to enrich the gene co-expression modules of diverse flowering time populations (FT) and floral bud differentiation stages (ST). In the MEyellow module, five core hub genes were identified, including CO14, GI, SPL8, SPL9, and SPL15. The correlation network of hub genes showed that they interact with SPLs, AP2, hormone response factors (auxin, gibberellin, ethylene, and abscisic acid), and several transcription factors (MADS-box transcription factor, bHLH, MYB, and NAC3). It suggests the important role of these genes and the complex molecular mechanism of floral bud differentiation and flowering time in L. radiata. These results can preliminarily explain the molecular mechanism of floral bud differentiation and provide new candidate genes for the flowering regulation of Lycoris.

Transcriptome analysis of floral bud development and function analysis of a novel CO gene in Paeonia × lemoinei 'High Noon'

Paeonia × lemoinei 'High Noon' is one of the most important cultivars in tree peony (Paeonia sect. Moutan), a traditional horticultural plant in China, with a re-blooming characteristic which was quite different from other cultivars. So, the genetic resources in 'High Noon' were incredibly valuable in flowering-time-modified molecular breeding in tree peony. However, the molecular mechanism underlying the floral bud formation of 'High Noon' was not clear yet. To explore the molecular mechanism in this process, the transcriptomes of three stages during floral bud development were deeply analyzed in this study. As a result, a total of 5816 differentially expressed genes (DEGs) were identified between the three developmental stages, and pathways including ''DNA replication'', ''metabolic pathways'', ''circadian rhythm'', and ''plant hormone signal transduction'' were mostly enriched in the functional enrichment and expression pattern analysis. Furthermore, a total of 584 genes related to the photoperiod pathway were further identified and a novel CO homolog gene PlCO was identified to be a stable hydrophilic protein, which contained both CCT domain and B-box domain. Over-expression of PlCO in Arabidopsis resulted in early flowering, which suggested a promotion role of flowering. The PlCO protein localized in nucleus and possessed a transcription activity ability, which implied that PlCO might function as a transcription factor. The transcriptome analysis revealed pathways involved in floral bud development in tree peony and provided new insight into the regulatory network underlying the floral bud development. The gene identification in 'High Noon' provided new valuable candidate genes for flowering-time-modified molecular breeding in tree peony.

Molecular mechanisms and evolutionary history of phytomelatonin in flowering

Flowering is a critical stage in plant life history, which is coordinated by environmental signals and endogenous cues. Phytomelatonin is a widely distributed indoleamine present in all living organisms and plays pleiotropic roles in plant growth and development. Recent evidence has established that phytomelatonin could modulate flowering in many species, probably in a concentration-dependent manner. Phytomelatonin seems to associate with floral meristem identification and floral organ formation, and the fluctuation of phytomelatonin might be important for flowering. Regarding the underlying mechanisms, phytomelatonin interacts with the central components of floral gene regulatory networks directly or indirectly, including the MADS-box gene family, phytohormones, and reactive oxygen species (ROS). From an evolutionary point of view, the actions of phytomelatonin in flowering probably evolved during the period of the diversification of flowering plants and could be regarded as a functional extension of its primary activities. The presumed evolutionary history of phytomelatonin-modulated flowering is proposed, presented in the chronological order of the appearance of phytomelatonin and core flowering regulators, namely DELLA proteins, ROS, and phytohormones. Further efforts are needed to address some intriguing aspects, such as the exploration of the association between phytomelatonin and photoperiodic flowering, phytomelatonin-related floral MADS-box genes, the crosstalk between phytomelatonin and phytohormones, as well as its potential applications in agriculture.

Plant clock modifications for adapting flowering time to local environments

During and after the domestication of crops from ancestral wild plants, humans selected cultivars that could change their flowering time in response to seasonal daylength. Continuous selection of this trait eventually allowed the introduction of crops into higher or lower latitudes and different climates from the original regions where domestication initiated. In the past two decades, numerous studies have found the causal genes or alleles that change flowering time and have assisted in adapting crop species such as barley (Hordeum vulgare), wheat (Triticum aestivum L.), rice (Oryza sativa L.), pea (Pisum sativum L.), maize (Zea mays spp. mays), and soybean (Glycine max (L.) Merr.) to new environments. This updated review summarizes the genes or alleles that contributed to crop adaptation in different climatic areas. Many of these genes are putative orthologs of Arabidopsis (Arabidopsis thaliana) core clock genes. We also discuss how knowledge of the clock's molecular functioning can facilitate molecular breeding in the future.

Identification of MADS-Box Transcription Factors in Iris laevigata and Functional Assessment of IlSEP3 and IlSVP during Flowering

Iris laevigata is ideal for gardening and landscaping in northeast China because of its beautiful flowers and strong cold resistance. However, the short length of flowering time (2 days for individual flowers) greatly limits its applications. Molecular breeding and engineering hold high potential for producing I. laevigata of desirable flowering properties. A prerequisite is to identify and characterize key flowering control genes, the identity of which remains largely unknown in I. laevigata due to the lack of genome information. To fill this knowledge gap, we used sequencing data of the I. laevigata transcriptome to identify MADS-box gene-encoding transcription factors that have been shown to play key roles in developmental processes, including flowering. Our data revealed 41 putative MADS-box genes, which consisted of 8 type I (5 Mα and 3 Mβ, respectively) and 33 type II members (2 MIKC* and 31 MIKCC, respectively). We then selected IlSEP3 and IlSVP for functional studies and found that both are localized to the nucleus and that they interact physically in vitro. Ectopic expression of IlSEP3 in Arabidopsis resulted in early flowering (32 days) compared to that of control plants (36 days), which could be mediated by modulating the expression of FT, SOC1, AP1, SVP, SPL3, VRN1, and GA20OX. By contrast, plants overexpressing IlSVP were phenotypically similar to that of wild type. Our functional validation of IlSEP3 was consistent with the notion that SEP3 promotes flowering in multiple plant species and indicated that IlSEP3 regulates flowering in I. laevigata. Taken together, this work provided a systematic identification of MADS-box genes in I. laevigata and demonstrated that the flowering time of I. laevigata can be genetically controlled by altering the expression of key MADS-box genes.

Genome-Wide Identification, Characterization, and Expression Profile Analysis of CONSTANS-like Genes in Woodland Strawberry (Fragaria vesca)

CONSTANS-like (CO-like) gene is one of the most important regulators in the flowering process of the plant, playing a core role in the photoperiodic flowering induction pathway. In this study, we identified 10 distinct CO-like genes (FveCOs) in woodland strawberry (Fragaria vesca). They were classified into three groups with specific gene structure characteristics or protein domains in each group. The effect of selection pressure on the FveCOs in the woodland strawberry was tested by Ka/Ks, and it was shown that the evolution rate of FveCOs was controlled by purification selection factors. Intraspecific synteny analysis of woodland strawberry FveCOs showed that at least one duplication event existed in the gene family members. Collinearity analysis of woodland strawberry genome with genomes of Arabidopsis, rice (Oryza sativa), and apple (Malus × domestica) showed that CO-like genes of F. vesca and Malus × domestica owned higher similarity for their similar genomes compared with those of other two species. The FveCOs showed different tissue-specific expression patterns. Moreover, real-time quantitative PCR results revealed that the expressions of the most FveCOs followed a 24-h rhythm oscillation under both long-day (LD) and short-day (SD) conditions. Further expression analysis showed that the individual expression changing profile of FveCO3 and FveCO5 was opposite to each other under both LD and SD conditions. Moreover, the expression of FveCO3 and FveCO5 was both negatively correlated with the flowering time variation of the woodland strawberry grown under LD and SD conditions, indicating their potential vital roles in the photoperiodic flowering regulation. Further protein interaction network analysis also showed that most of the candidate interaction proteins of FveCO3 and FveCO5 were predicted to be the flowering regulators. Finally, LUC assay indicated that both FveCO3 and FveCO5 could bind to the promoter of FveFT1, the key regulator of flowering regulation in the woodland strawberry, and thus activate its expression. Taken together, this study laid a foundation for understanding the exact roles of FveCOs in the reproductive development regulation of the woodland strawberry, especially in the photoperiodic flowering process.

The high concentrations of abscisic, jasmonic, and salicylic acids produced under long days do not accelerate flowering in Chenopodium ficifolium 459

The survival and adaptation of angiosperms depends on the proper timing of flowering. The weedy species Chenopodium ficifolium serves as a useful diploid model for comparing the transition to flowering with the important tetraploid crop Chenopodium quinoa due to the close phylogenetic relationship. The detailed transcriptomic and hormonomic study of the floral induction was performed in the short-day accession C. ficifolium 459. The plants grew more rapidly under long days but flowered later than under short days. The high levels of abscisic, jasmonic, and salicylic acids at long days were accompanied by the elevated expression of the genes responding to oxidative stress. The increased concentrations of stress-related phytohormones neither inhibited the plant growth nor accelerated flowering in C. ficifolium 459 at long photoperiods. Enhanced content of cytokinins and the stimulation of cytokinin and gibberellic acid signaling pathways under short days may indicate the possible participation of these phytohormones in floral initiation. The accumulation of auxin metabolites suggests the presence of a dynamic regulatory network in C. ficifolium 459.

LsMYB15 Regulates Bolting in Leaf Lettuce (Lactuca sativa L.) Under High-Temperature Stress

High temperature is one of the primary environmental stress factors affecting the bolting of leaf lettuce. To determine the potential role of melatonin in regulating high-temperature induced bolting in leaf lettuce (Lactuca sativa L.), we conducted melatonin treatment of the bolting-sensitive cultivar "S39." The results showed that 100 μmol L^-1 melatonin treatment significantly promoted growth, and melatonin treatment delayed high-temperature-induced bolting in lettuce. RNA-seq analysis revealed that the differentially expressed genes (DEGs) involved in "plant hormone signal transduction" and "phenylpropanoid biosynthesis" were significantly enriched during high-temperature and melatonin treatment. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis suggested that the expression patterns of abscisic acid (ABA)-related genes positively correlated with stem length during leaf lettuce development. Furthermore, weighted gene co-expression network analysis (WGCNA) demonstrated that MYB15 may play an important role in melatonin-induced resistance to high temperatures. Silencing the LsMYB15 gene in leaf lettuce resulted in early bolting, and exogenous melatonin delayed early bolting in leaf lettuce at high temperatures. Our study provides valuable data for future studies of leaf lettuce quality.

Transcriptome Analysis of Lycoris chinensis Bulbs Reveals Flowering in the Age-Mediated Pathway

Lycoris is a summer bulbous flower that commonly needs to go through a long period of vegetative growth for 3 to 5 years before flowering. Plant flowering is regulated by a complex genetic network. Compared with most perennial flowers, knowledge on the molecular mechanism responsible for floral transition in bulbous flowers is lacking, and only a few genes that regulate flowering have been identified with few reports on the floral transition in Lycoris. In this study, we identified many differentially expressed genes (DEGs) and transcription factors (TFs) by RNA-Seq in L. chinensis bulbs of different ages, including one- to four-year-old nonflowering bulbs and four-year-old flowering bulbs. Some DEGs were enriched in Gene Ontology (GO) terms between the three- and four-year-old bulbs, and there most genes were enriched in terms of metabolic process and catalytic activity. In the four-year old bulbs, most of the DEGs that may be involved in flowering were classified under the GO term biological process, which was a totally different result from the vegetative bulbs. Some DEGs between flowering and nonflowering bulbs were enriched in plant hormone signal transduction, including the hormones auxin, cytokinin, abscisic acid, and ethylene, but no DEGs were enriched in the gibberellin pathway. Auxin is the main endogenous phytohormone involved in bulb growth and development, but cytokinin, abscisic acid, and ethylene were shown to increase in flowering bulbs. In addition, energy-metabolism-related genes maintain a high expression level in large bulbs, and some positive regulators (SPL, COL, and AP1) and early flowering genes were also shown to be highly expressed in the meristems of flowering bulbs. It suggested that sugar molecules may be the energy source that regulates the signal transduction of flowering by connecting with phytohormone signaling in Lycoris. A total of 1911 TFs were identified and classified into 89 categories, where the top six families with the largest gene numbers were C2H2, NAC, AP2/ERF-ERF, C3H, MYB-related, and WRKY. Most DEGs were in the AP2/ERF-ERF family, and most of them were downregulated in 4-year-old flowering bulbs. A number of families were reported to be involved in plant flowering, including NAC, AP2/ERF, MYB, WRKY, bZIP, MADS, and NF-Y. These results can act as a genetic resource to aid in the explanation of the genetic mechanism responsible for the flowering of Lycoris and other bulbous flowers.

Cytokinin increases vegetative growth period by suppressing florigen expression in rice and maize

Increasing the vegetative growth period of crops can increase biomass and grain yield. In rice (Oryza sativa), the concentration of trans -zeatin, an active cytokinin, was high in the leaves during vegetative growth and decreased rapidly upon induction of florigen expression, suggesting that this hormone is involved in the regulation of the vegetative phase. To elucidate whether exogenous cytokinin application influences the length of the vegetative phase, we applied 6-benzylaminopurine (BAP) to rice plants at various developmental stages. Our treatment delayed flowering time by 8-9 days when compared with mock-treated rice plants, but only at the transition stage when the flowering signals were produced. Our observations also showed that flowering in the paddy field is delayed by thidiazuron, a stable chemical that mimics the effects of cytokinin. The transcript levels of florigen genes Heading date 3a (Hd3a) and Rice Flowering locus T1 (RFT1) were significantly reduced by the treatment, but the expression of Early heading date 1 (Ehd1), a gene found directly upstream of the florigen genes, was not altered. In maize (Zea mays), similarly, BAP treatment increased the vegetative phage by inhibiting the expression of ZCN8, an ortholog of Hd3a. We showed that cytokinin treatment induced the expression of two type-A response regulators (OsRR1 and OsRR2) which interacted with Ehd1, a type-B response regulator. We also observed that cytokinin did not affect flowering time in ehd1 knockout mutants. Our study indicates that cytokinin application increases the duration of the vegetative phase by delaying the expression of florigen genes in rice and maize by inhibiting Ehd1.

Time-Course Transcriptomic Profiling of Floral Induction in Cultivated Strawberry

The initiation and quality of flowering directly affect the time to market and economic benefit of cultivated strawberries, but the underlying mechanisms of these processes are largely unknown. To investigate the gene activity during the key period of floral induction in strawberries, time-course transcriptome analysis was performed on the shoot apex of the strawberry cultivar ‘Benihoppe.’ A total of 7177 differentially expressed genes (DEGs) were identified through pairwise comparisons. These DEGs were grouped into four clusters with dynamic expression patterns. By analyzing the key genes in the potential flowering pathways and the development of the leaf and flower, at least 73 DEGs that may be involved in the regulatory network of floral induction in strawberries were identified, some of which belong to the NAC, MYB, MADS, and SEB families. A variety of eight hormone signaling pathway genes that might play important roles in floral induction were analyzed. In particular, the gene encoding DELLA, a key inhibitor of the gibberellin signaling pathway, was found to be significantly differentially expressed during the floral induction. Furthermore, the differential expression of some important candidate genes, such as TFL1, SOC1, and GAI-like, was further verified by qRT-PCR. Therefore, we used this time-course transcriptome data for a preliminary exploration of the regulatory network of floral induction and to provide potential candidate genes for future studies of flowering in strawberries.

Nitrilases NIT1/2/3 Positively Regulate Flowering by Inhibiting MAF4 Expression in Arabidopsis

Three of the nitrilases (NITs), NIT1, NIT2, and NIT3, are ubiquitously existing in plant kingdom, which catalyze indole-3-acetonitrile into the most important auxin indole-3-acetic acid. Auxin is an indispensable hormone, which plays the important roles in almost all processes of plant growth and development. However, there are few reports on the regulation of flowering-time mediated by auxin. Here, we found that in Arabidopsis, nit1/2/3 showed a late flowering phenotype in short days. To explore the molecular mechanism by which NIT1/2/3 regulate flowering time, we performed transcriptome sequencing of nit1/2/3. The results showed that the expression of a MADS-box transcription factor gene MADS AFFECTING FLOWERING4 (MAF4) was dramatically increased in nit1/2/3 comparing to wild type (WT). MAF4 is one of the paralogs of the potent flowering inhibitor FLOWERING LOCUS C (FLC). There are four other paralogs in FLC clade in Arabidopsis, including FLOWERING LOCUS M (FLM/MAF1), MAF2, MAF3, and MAF5. The late flowering phenotype of nit1/2/3 could not be observed in the maf4 background, indicating that the phenotype was specifically dependent on MAF4 rather than other FLC clade members. Interestingly, the expression of a lncRNA gene MAS, which is transcribed in the opposite direction of MAF4, was found significantly increased in nit1/2/3. Also, MAS has been reported to activate MAF4 transcription by promoting histone 3 lysine 4 trimethylation (H3K4me3). As expected, H3K4me3 deposition at MAF4 locus in nit1/2/3 was highly enriched and significantly higher than that of WT. In summary, we show that NITs, NIT1/2/3, positively regulate flowering by repressing MAF4 through manipulating H3K4me3 modification. Further study needs to be performed to explore the largely unknown mechanisms behind it.

The kinesin-13 protein BR HYPERSENSITIVE 1 is a negative brassinosteroid signaling component regulating rice growth and development

Phytohormones performed critical roles in regulating plant architecture and thus determine grain yield in rice. However, the roles of brassinosteroids (BRs) compared to other phytohormones in shaping rice architecture are less studied. In this study, we report that BR hypersensitive1 (BHS1) plays a negative role in BR signaling and regulate rice architecture. BHS1 encodes the kinesin-13a protein and regulates grain length. We found that bhs1 was hypersensitive to BR, while BHS1-overexpression was less sensitive to BR compare to WT. BHS1 was down-regulated at RNA and protein level upon exogenous BR treatment, and proteasome inhibitor MG132 delayed the BHS1 degradation, indicating that both the transcriptional and posttranscriptional regulation machineries are involved in BHS1-mediated regulation of plant growth and development. Furthermore, we found that the BR-induced degradation of BHS1 was attenuated in Osbri1 and Osbak1 mutants, but not in Osbzr1 and Oslic mutants. Together, these results suggest that BHS1 is a novel component which is involved in negative regulation of the BR signaling downstream player of BRI1.

Conserved and distinct roles of H3K27me3 demethylases regulating flowering time in Brassica rapa

Epigenetic regulation is necessary for optimal organism development and preservation of gene expression profiles in the cell. In plants, the trimethylation of histone H3 lysine 27 (H3K27me3) is a silencing epigenetic mark relevant for developmental transitions like flowering. The floral transition is a key agronomic trait; however, the epigenetic mechanisms of flowering time regulation in crops remain poorly understood. Here we study the Jumonji H3K27me3 demethylases BraA.REF6 and BraA.ELF6 in Brassica rapa. Phenotypic characterization of novel mutant lines and genome-wide H3K27me3 chromatin immunoprecipitation and transcriptomic analyses indicated that BraA.REF6 plays a greater role than BraA.ELF6 in fine-tuning H3K27me3 levels. In addition, we found that braA.elf6 mutants were early flowering due to high H3K27me3 levels at B. rapa homologs of the floral repressor FLC. Unlike mutations in Arabidopsis thaliana, braA.ref6 mutants were late flowering without altering the expression of B. rapa FLC genes. Remarkably, we found that BraA.REF6 regulated a number of gibberellic acid (GA) biosynthetic genes, including a homolog of GA1, and that GA-treatment complemented the late flowering mutant phenotype. This study increases our understanding of the epigenetic regulation of flowering time in B. rapa, highlighting conserved and distinct regulatory mechanisms between model and crop species.

Exogenous GA3 promotes flowering in Paphiopedilum callosum (Orchidaceae) through bolting and lateral flower development regulation

Paphiopedilum orchids have a high ornamental value, and their flower abundance and timing are both key horticultural traits regulated by phytohormones. All one-flowered Paphiopedilum have additional lateral buds in the apical bract that fail to develop. In this study, an exogenous gibberellin (GA₃) application promoted flowering of Pathiopedilum callosum by inducing its early bolting instead of the floral transition of dominant flowers. Applying GA₃ effectively promoted lateral flower differentiation, resulting in a two-flowered inflorescence. GA-promoted lateral flower formation involved GA interacting with indole-3-acetic acid (IAA) and cytokinins (CTKs), given the decreased CTK content and downregulated expression of CTK synthesis genes, the increased IAA content and downregulated expression of IAA degradation, and the upregulated expression of transport genes. Further, GA acted via PcDELLA, PcTCP15, and PcXTH9 expressed in stage 5 to promote bolting, and via expression of PcAP3, PcPI, and PcSEP to promote flowering. This study provides insight into mechanisms regulating flower development of P. callosum.