Flowering Process Research Articles

Strigolactone and Auxin Applications on Cotyledon Senescence in Sunflower Seedlings under Salt Stress

Objective: Senescence is a programmed cell death process and is important in the growth, development and flowering process of the plant. Delaying senescence has a very important effect on agriculture in terms of product yield. Indole-3- acetic acid (IAA) and strigolactone (GR24) are growth regulators that affect plant development and senescence. Salt stress accelerates the senescence process. The aim of this study is to increase crop yield by delaying senescence by the application of auxin and GR24 under stress conditions, because the delay of senescence causes the prolongation of the vegetative process and the formation of more apical tips. In this case, the seedling produces more fruit. Materials and Methods: In this study, senescent cotyledons of sunflower seedlings were used as experimental material. Half of the developing sunflower seedlings were irrigated with Hoagland solution, and the other half was irrigated with 150 mM sodium chloride (NaCl) solution. IAA and GR24 were applied by spraying on seedlings that are grown both in Hoagland solution and under salt stress. Results: The degree of senescence of the cotyledons of the plants was determined in terms of the percentage of green area. When the green area percentage of cotyledons of seedlings grown in Hoagland solution was 50, all cotyledons were harvested. After that, fresh weight, pigment contents, total protein, malondialdehyde, and proline levels, peroxidase enzyme activities of cotyledons were determined. The application of IAA and GR24 to the cotyledons of seedlings grown in the salt medium significantly delayed the senescence. Conclusion: This study was conducted in the plant growth chamber under controlled conditions. Results showed that the application of IAA and GR24 to leaves can ameliorate the adverse effects of salt stress and delay senescence due to the activation of chlorophyll components and modulation of photosynthesis as well as antioxidant defense capacity. The effect of IAA is more precise when all analyzes are considered. More importantly, showed that all findings (except MDA and Proline) IAA and GR24 promote senescence in Hoagland in this research. Delaying senescence contributes to basic science. It is desired to increase fruit and vegetable yield by delaying senescence. It is suggested that this information can be used practically in the field of agriculture. On the other hand in this study, we can say that IAA and relatively GR24 can play an important role in the protection of plants in agricultural areas in salt stress.

Genome-Wide Identification of MIKCc-Type MADS-Box Family Gene and Floral Organ Transcriptome Characterization in Ma Bamboo (Dendrocalamus latiflorus Munro).

Most bamboos die after flowering, and the molecular mechanisms responsible for flowering is poorly understood. The MIKCc-type MADS-box family gene is involved in the flowering process. To explore the mechanism of the MIKCc-type MADS-box gene and phytohormone regulation in the flowering of Dendrocalamus latiflorus Munro (D. latiflorus), characterized by extremely rapid growth and widely cultivated woody bamboo, we initially did a genome-wide analysis of the MIKCc-type MADS-box gene in D. latiflorus. In the meantime, transcriptome analysis was performed using the floral organs. A total of 170 MIKCc-Type MADS-Box genes were identified and divided into 15 categories. The cis-acting element analysis in promoters regions revealed that MIKC-type MADS-box family genes were associated with hormones, including auxin, abscisic acid (ABA), gibberellin (GA) and jasmonic acid (JA), which was found at 79, 476, 96, 486 sites and cover 61, 103, 73, 128 genes. Genome synteny analysis showed subgenome AA and BB were better than CC and obtained 49, 40, 39 synteny genes compared with Oryza sativa (O. sativa). In transcriptome analysis of floral organs, the enriched pathway from DEGs included circadian, vernalization and gibberellin pathways associated with the flowering process. We found that the jasmonic acid synthesis gene is highly expressed in the pistil, which may be the cause of Ma bamboo pollen abortion. The expression profile showed that most MIKC-type MADS-box genes exhibited high expression in flower organs. The consequences of this study will provide insight into the irregular flowering and low pollen counts of Ma bamboo.

Metabolic analysis of the regulatory mechanism of sugars on secondary flowering in Magnolia

BackgroundMagnolia, a traditional and important ornamental plant in urban greening, has been cultivated for about 2000 years in China for its elegant flower shape and gorgeous flower color. Most varieties of Magnolia bloom once a year in spring, whereas a few others, such as Magnolia liliiflora Desr. ‘Hongyuanbao’, also bloom for the second time in summer or early autumn. Such a twice flowering trait is desirable for its high ornamental value, while its underlying mechanism remains unclear.MethodsParaffin section was used to show the flowering time and phenotypic changes of M. liliiflora ‘Hongyuanbao’ during the twice flowering periods from March 28 to August 25, 2018. Gas chromatography-mass spectrometry (GC-MS) was then performed to explore the chemical metabolites through the twice flower bud differentiation process in ‘Hongyuanbao’, and the metabolites were screened and identified by orthogonal projection to latent structures discriminant analysis (OPLS-DA). Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis (KEGG) was used to reveal the relationship between the sugar metabolites and twice-flowering characteristic. To further investigate the potential role of sucrose and trehalose on flowering regulation of ‘Hongyuanbao’, the plants once finished the spring flowering were regularly sprayed with sucrose and trehalose solutions at 30 mM, 60 mM, and 90 mM concentrations from April 22, 2019. The flower bud differentiation processes of sprayed plants were observed and the expression patterns of the genes involved in sucrose and trehalose metabolic pathways were studied by quantitative reverse transcription PCR (qRT-PCR).ResultsIt showed that ‘Hongyuanbao’ could complete flower bud differentiation twice in a year and flowered in both spring and summer. The metabolites of flower bud differentiation had a significant variation between the first and second flower buds. Compared to the first flower bud differentiation process, the metabolites in the sucrose and trehalose metabolic pathways were significantly up-regulated during the second flower bud differentiation process. Besides that, the expression levels of a number of trehalose-6-phosphate synthase (TPS) genes including MlTPS1, MlTPS5, MlTPS6, MlTPS7 and MlTPS9 were substantially increased in the second flower differentiation process compared with the first process. Exogenous treatments indicated that compared to the control plants (sprayed with water, CK), all three concentrations of trehalose could accelerate flowering and the effect of 60 mM concentration was the most significant. For the sucrose foliar spray, only the 60 mM concentration accelerated flowering compared with CK. It suggested that different concentration of trehalose and sucrose might have different effects. Expression analysis showed that sucrose treatment increased the transcription levels of MlTPS5 and MlTPS6, whereas trehalose treatment increased MlTPS1, showing that different MlTPS genes took part in sucrose and trehalose metabolic pathways respectively. The expression levels of a number of flowering-related genes, such as MlFT, MlLFY, and MlSPL were also increased in response to the sprays of sucrose and trehalose.ConclusionsWe provide a novel insight into the effect of sucrose and trehalose on the flowering process in Magnolia. Under the different sugar contents treatments, the time of flower bud differentiation of Magnolia was advanced. Induced and accelerated flowering in response to sucrose and trehalose foliar spray, coupled with elevated expression of trehalose regulatory and response genes, suggests that secondary flower bud formation is a promoted by altered endogenous sucrose and trehalose levels. Those results give a new understanding of sucrose and trehalose on twice-flowering in Magnolia and provide a preliminary speculation for inducing and accelerating the flowering process in Magnolia.

In Vitro Florigenesis with Special Reference to Orchids- A Review.

Orchids are widely used in floriculture as attractive cut flowers all over the world. The current paper reviews factors affecting the in vitro flowering in orchid species. The phenomenon of in vitro flowering is advantageous as it shortens the breeding cycle, which is prolonged in the in vivo grown orchid species of commercial value. Certain genetic and biochemical mechanisms are involved at the time of onset of flowering in orchid plants. In the present endeavour, efforts have been made to initiate in vitro flowering in terrestrial and epiphytic orchid species. Various phenomenon involved during transition of vegetative shoot apex into floral axis is also reviewed. In vitro flowering was induced in Dendrobium nobile and Zeuxine strateumatica in Mitra medium supplemented with BAP at 0.5 in mgl-1. In vitro flowering can be initiated by manipulating physical and chemical stimulus in the nutrient regime. The study would be helpful in better understanding the complex process of flowering in vitro as well as ex vitro.

Decoding Gene Expression Signatures Underlying Vegetative to Inflorescence Meristem Transition in the Common Bean

The tropical common bean (Phaseolus vulgaris L.) is an obligatory short-day plant that requires relaxation of the photoperiod to induce flowering. Similar to other crops, photoperiod-induced floral initiation depends on the differentiation and maintenance of meristems. In this study, the global changes in transcript expression profiles were analyzed in two meristematic tissues corresponding to the vegetative and inflorescence meristems of two genotypes with different sensitivities to photoperiods. A total of 3396 differentially expressed genes (DEGs) were identified, and 1271 and 1533 were found to be up-regulated and down-regulated, respectively, whereas 592 genes showed discordant expression patterns between both genotypes. Arabidopsis homologues of DEGs were identified, and most of them were not previously involved in Arabidopsis floral transition, suggesting an evolutionary divergence of the transcriptional regulatory networks of the flowering process of both species. However, some genes belonging to the photoperiod and flower development pathways with evolutionarily conserved transcriptional profiles have been found. In addition, the flower meristem identity genes APETALA1 and LEAFY, as well as CONSTANS-LIKE 5, were identified as markers to distinguish between the vegetative and reproductive stages. Our data also indicated that the down-regulation of the photoperiodic genes seems to be directly associated with promoting floral transition under inductive short-day lengths. These findings provide valuable insight into the molecular factors that underlie meristematic development and contribute to understanding the photoperiod adaptation in the common bean.

Citrus VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1) interacts with CuFT1 and CuFT3, affecting flowering in transgenic Arabidopsis

Understanding the flowering process is essential for developing methods to shorten the breeding period and regulate the yield of tree fruits, such as Satsuma mandarin (Citrus unshiu Marc.). In the flowering network system in Arabidopsis, FLOWERING LOCUS T (FT) acts as a transmissible floral inducer. In this study, a citrus ortholog of the transcription factor (TF) VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1)-like gene, CuVOZ1, and two FT-like genes, CuFT1 and CuFT3, were isolated from the Satsuma mandarin ‘Aoshima’. Protein-protein interaction between CuVOZ1 and CuFTs was confirmed in vitro with a yeast two-hybrid (Y2H) system. N-terminal 400 amino acids of CuVOZ1, consisting of three motifs, namely, domain of unknown function 4749 (DUF4749), no apical meristem (NAM), and a zinc coordination motif, were assumed to be involved in the CuVOZ1–CuFT1 and CuVOZ1–CuFT3 complexes. Docking simulation suggested that only the zinc coordination motif of CuVOZ1 was possibly involved in the CuVOZ1–CuFT3 interaction and that the phosphatidylethanolamine-binding protein (PBP) motif in exon 4 of CuFTs was predicted to be crucial for the interaction between CuVOZ1 and CuFTs. The distance between the amino acid residues involved in docking was predicted to be from 2.69 to 3.37 Å, suggesting that the forces between CuVOZ1 and CuFTs in the CuVOZ1–CuFT complexes were weak Van der Waals forces. Constitutive expression of CuVOZ1 in Arabidopsis affected the flowering time, plant size, morphology of inflorescence, number of flowers and siliques, and formation of flower buds on the elongated stem. It was suggested that CuVOZ1 might act as a trigger for early flowering and might be involved in the elongation and branching of the inflorescence. The CuVOZ1–CuFT complexes might regulate cellular proliferation and the formation of new tissues and affect both vegetative and reproductive development.

Expression Analysis of Brassinolide-Metabolism-Related Genes at Different Growth Stages of Pak Choi

Pak choi needs to be exposed to low temperature (vernalized) before flowering will initiate. Early bolting caused by low temperature often occurs in spring and leads to significant economic losses. Therefore, it is of great practical significance to study the flowering process of pak choi. Brassinolide (BR) plays a certain role in the flowering process of pak choi. In order to better understand the role of BR in the flowering process of pak choi, the BR content in the shoot apices of pak choi at different growth stages was determined by enzyme-linked immunosorbent assay (ELISA). The results showed that the BR content increased after low-temperature treatment. With the progress of vegetative growth, the BR content decreased and reached the lowest at 10 days after transplanting (V10), then the content increased and reached a small peak at the critical period of floral bud differentiation (S0). After initiation of floral bud differentiation, the content decreased at floral bud differentiation stage 1 (S1), and then gradually increased and reached a peak at floral bud differentiation stage 3 (S3). In order to clarify the molecular mechanism of BR content changes, we analyzed the expressions of key enzymes coding genes in the BR metabolic pathway, and found that six major synthase-encoding genes (Bra008760, Bra030023, Bra036097, Bra027405, Bra011678, and Bra025409) were upregulated at the critical period of floral bud differentiation, leading to the increase in BR content, which were consistent with changes in the BR content. By analyzing the functions of differentially expressed genes (DEGs) between the vegetative growth stage (V10) and the critical period of floral bud differentiation (S0), 21 DEGs were found to be related to BR metabolism. These findings can provide a reference for elucidating the molecular mechanism of BR regulating the flowering process of pak choi.

Genome-Wide Identification and Expression Analysis of the MADS-Box Family in Ginkgo biloba

As the most significant transformation stage of plants, the flowering process has typically been the focus of research. MADS-box gene plays an important regulatory role in flower development. In this study, 26 MADS-box genes were identified from Ginkgo biloba, including 10 type-I genes and 16 type-II genes, which were distributed on eight chromosomes. There was no collinearity between the GbMADS genes, and the homology with genes from other species was low. All GbMADS proteins contain conserved MADS domains. The gene structures of GbMADS in the same gene family or subfamily differed, but the conserved protein motifs had similar distributions. The microRNA (miRNA) target sites of the GbMADS genes were predicted. It was found that the expression of 16 GbMADS genes may be regulated by miRNA. The results of cis-acting element analysis showed that the 26 GbMADS genes contained a large number of hormones regulated and light-responsive elements as well as stress-response elements. Furthermore, the quantitative real-time PCR (qRT-PCR) experimental results showed that most GbMADS genes were differentially expressed in the male and female flowers at different developmental stages. Among them, the only MIKC * gene GbMADS16 has the highest expression in the metaphase development of the microstrobilus (M2) stage and is almost not expressed in female flowers. Taken together, these findings suggest that the MADS-box genes may play an important role in the development and differentiation of G. biloba flowers.

Genome-Wide Analysis of SQUAMOSA-Promoter-Binding Protein-like Family in Flowering Pleioblastus pygmaeus.

SQUAMOSA Promoter-Binding Protein-Like (SPL) family is well-known for playing an important role in plant growth and development, specifically in the reproductive process. Bamboo plants have special reproductive characteristics with a prolonged vegetative phase and uncertain flowering time. However, the underlying functions of SPL genes in reproductive growth are undisclosed in bamboo plants. In the study, a total of 28 SPLs were screened from an ornamental dwarf bamboo species, Pleioblastus pygmaeus. Phylogenetic analysis indicates that 183 SPLs from eight plant species can be classified into nine subfamilies, and the 28 PpSPLs are distributed among eight subfamilies. Homologous analysis shows that as many as 32 pairs of homologous genes were found between P. pygmaeus and rice, and 83 pairs were found between P. pygmaeus and Moso bamboo, whose Ka/Ks values are all <1. MiRNA target prediction reveals that 13 out of the 28 PpSPLs have recognition sites complementary to miRNA156. To screen the SPLs involved in the reproductive growth of bamboo plants, the mRNA abundance of the 28 PpSPLs was profiled in the different tissues of flowering P. pygmaeus and non-flowering plants by RNA-Seq. Moreover, the relative expression level of eight PpSPLs is significantly higher in flowering P. pygmaeus than that in non-flowering plants, which was also validated by RT-qPCR. Combined with phylogenetic analysis and homologous analysis, the eight significant, differentially expressed PpSPLs were identified to be associated with the reproductive process and flower organ development. Among them, there are four potential miRNA156-targeting PpSPLs involved in the flowering process. Of significant interest in the study is the identification of 28 SPLs and the exploration of four key flowering-related SPLs from P. pygmaeus, which provides a theoretic basis for revealing the underlying functions of SPLs in the reproductive growth of bamboo plants.

The influence of temperature on the phenology of apple trees grown in mild winter regions of Brazil, based on long-term records

Phenological events, such as flowering, are highly responsive to temperature and are directly influenced by the establishment of a dormancy period in temperate fruit trees. Increased temperatures, due to climate change, can cause advancement, delay or no change to temperate fruit tree flowering, putting production at risk and raising uncertainty about the future of crops in traditional apple producing regions. The objective of this work was to evaluate the effect of temperatures on the endodormancy and ecodormancy periods, and how they directly influence the flowering dates of apple trees grown in contrasting areas in a subtropical climate region. Phenological and climate data were obtained from orchards located in the São Joaquim – SC (SJ), Caçador – SC (CA) and Palmas – PR (PA), in Southern Brazil. The climate of all three areas is considered Cfb using the Köppen classification. First flowering date data for the apple cultivars Fuji and Gala were collected for 43 and 45 years at São Joaquim – SC, respectively for Fuji and Gala, for 39 years at Caçador – SC for both cultivars and for 9 years at Palmas – PR for both cultivars. The flowering date data were correlate with the daily mean temperatures during the year, using PLS analysis. Chill and heat accumulations were also calculated during the periods of chill and heat sensitivity (endodormancy and ecodormancy) delineated by PLS analysis. The PLS proved to be efficient at identifying periods where there was chill and heat accumulation by the apple tree in a subtropical region (mild winter region). The start date of flowering is influenced by temperatures during both the chilling and forcing periods. At CA and PA, the mean temperatures increased over the years, and the plants, especially the gala cultivar at CA, responded to this temperature increase with a significant change in their flowering date. At SJ, the coldest locality, temperature and phenology changes were not significant. The chill and heat requirements are different according to region and cultivar. When cultivars are exposed to conditions of low chill accumulation, the tendency is for heat requirement to increase. For the next few years, the temperature during the period of endodormancy could be a more decisive factor for the flowering process

Effect of exogenous putrescine on flower growth, post-harvest quality and root mycorrhizal development of gerbera (Gerbera jamesonii cv. Dune) cut flowers

• Putrescine increases the rate of mycorrhiza colonization in the root. • Putrescine and mycorrhiza improved the quality of gerbera cut flowers. • Putrescine and mycorrhizal inoculation maintained the quality of gerbera cut flowers during vase life period. Effect of putrescine on the rate of mycorrhiza colonization in root and their effect on the growth and flowering process of gerbera ‘Dune’ was investigated in the form of factorial trial in a completely randomized design with three replications in a greenhouse. The factors were four concentrations of putrescine (0, 1, 2, and 4 mM) as foliar application and mycorrhizal fungus (without and with inoculation). The Mycorrhizal fungus was inoculated when plantlets transfer to pots, and two weeks after establishment; putrescine foliar application was performed every 15 days-interval for three months. Morphological and physiological characteristics measured in this research were included the number of flowers per plant, the time of bud formation until flowering, flower diameter, fresh and dry weight of flowers, flower longevity, total phenol, and leaf anthocyanin, as well as symbiosis percentages. The results showed that foliar application of putrescine increased mycorrhiza colonization in roots, and the highest colonization was obtained at the concentration of 2 mM putrescine application. Also, their interaction had a positive effect on other measured traits compared to the control. Putrescine and mycorrhiza increased the quality of gerbera cut flowers and reduced ions leakage, hydrogen peroxide, malondialdehyde, and lipoxygenase activity, and increased ascorbate peroxidase activity.

Using bioelectrohydrogenesis left-over residues as a future potential fertilizer for soil amendment

In this current research, the left-over residues collected from the dark fermentation-microbial electrolysis cells (DF-MEC) integrated system solely biocatalyzed by activated sludge during the bioconversion of the agricultural straw wastes into hydrogen energy, was investigated for its feasibility to be used as a potential alternative biofertilizer to the commonly costly inorganic ones. The results revealed that the electrohydrogenesis left-over residues enriched various plant growth-promoting microbial communities including Enterobacter (8.57%), Paenibacillus (1.18%), Mycobacterium (0.77%), Pseudomonas (0.65%), Bradyrhizobium (0.12%), Azospirillum (0.11%), and Mesorhizobium (0.1%) that are generally known for their ability to produce different essential phytohormones such as indole-3-acetic acid/indole acetic acid (IAA) and Gibberellins for plant growth. Moreover, they also contain both phosphate-solubilizing and nitrogen-fixing microbial communities that remarkably provide an adequate amount of assimilable phosphorus and nitrogen required for enhanced plants or crop growth. Furthermore, macro-, and micronutrients (including N, P, K, etc.) were all analyzed from the residues and detected adequate appreciate concentrations required for plant growth promotions. The direct application of MEC-effluent as fertilizer in this current study conspicuously promoted plant growth (Solanum lycopersicum L. (tomato), Capsicum annuum L. (chilli), and Solanum melongena L. (brinjal)) and speeded up flowering and fruit-generating processes. Based on these findings, electrohydrogenesis residues could undoubtedly be considered as a potential biofertilizer. Thus, this technology provides a new approach to agricultural residue control and concomitantly provides a sustainable, cheap, and eco-friendly biofertilizer that could replace the chemical costly fertilizers.

Identification of long non-coding RNAs involved in floral scent of Rosa hybrida.

Long non-coding RNAs (lncRNAs) were found to play important roles in transcriptional, post-transcriptional, and epigenetic gene regulation in various biological processes. However, lncRNAs and their regulatory roles remain poorly studied in horticultural plants. Rose is economically important not only for their wide use as garden and cut flowers but also as important sources of natural fragrance for perfume and cosmetics industry, but presently little was known about the regulatory mechanism of the floral scent production. In this paper, a RNA-Seq analysis with strand-specific libraries, was performed to rose flowers in different flowering stages. The scented variety ‘Tianmidemeng’ (Rosa hybrida) was used as plant material. A total of 13,957 lncRNAs were identified by mining the RNA-Seq data, including 10,887 annotated lncRNAs and 3070 novel lncRNAs. Among them, 10,075 lncRNAs were predicted to possess a total of 29,622 target genes, including 54 synthase genes and 24 transcription factors related to floral scent synthesis. 425 lncRNAs were differentially expressed during the flowering process, among which 19 were differentially expressed among all the three flowering stages. Using weighted correlation network analysis (WGCNA), we correlate the differentially-expressed lncRNAs to synthesis of individual floral scent compounds. Furthermore, regulatory function of one of candidate lncRNAs for floral scent synthesis was verified using VIGS method in the rose. In this study, we were able to show that lncRNAs may play important roles in floral scent production in the rose. This study also improves our understanding of how plants regulate their secondary metabolism by lncRNAs.

Genome-Wide Identification and Analysis of the MADS-Box Gene Family in Almond Reveal Its Expression Features in Different Flowering Periods.

The MADS-box gene family is an important family of transcription factors involved in multiple processes, such as plant growth and development, stress, and in particular, flowering time and floral organ development. Almonds are the best-selling nuts in the international fruit trade, accounting for more than 50% of the world’s dried fruit trade, and one of the main economic fruit trees in Kashgar, Xinjiang. In addition, almonds contain a variety of nutrients, such as protein and dietary fiber, which can supplement nutrients for people. They also have the functions of nourishing the yin and kidneys, improving eyesight, and strengthening the brain, and they can be applied to various diseases. However, there is no report on the MADS-box gene family in almond (Prunus dulcis). In this study, a total of 67 PdMADS genes distributed across 8 chromosomes were identified from the genome of almond ‘Wanfeng’. The PdMADS members were divided into five subgroups—Mα, Mβ, Mγ, Mδ, and MIKC—and the members in each subgroup had conserved motif types and exon and intron numbers. The number of exons of PdMADS members ranged from 1 to 20, and the number of introns ranged from 0 to 19. The number of exons and introns of different subfamily members varied greatly. The results of gene duplication analysis showed that the PdMADS members had 16 pairs of segmental duplications and 9 pairs of tandem duplications, so we further explored the relationship between the MADS-box gene members in almond and those in Arabidopsis thaliana, Oryza sativa, Malus domestica, and Prunus persica based on colinear genes and evolutionary selection pressure. The results of the cis-acting elements showed that the PdMADS members were extensively involved in a variety of processes, such as almond growth and development, hormone regulation, and stress response. In addition, the expression patterns of PdMADS members across six floral transcriptome samples from two almond cultivars, ‘Wanfeng’ and ‘Nonpareil’, had significant expression differences. Subsequently, the fluorescence quantitative expression levels of the 15 PdMADS genes were highly similar to the transcriptome expression patterns, and the gene expression levels increased in the samples at different flowering stages, indicating that the two almond cultivars expressed different PdMADS genes during the flowering process. It is worth noting that the difference in flowering time between ‘Wanfeng’ and ‘Nonpareil’ may be caused by the different expression activities of PdMADS47 and PdMADS16 during the dormancy period, resulting in different processes of vernalization. We identified a total of 13,515 target genes in the genome based on the MIKC DNA-binding sites. The GO and KEGG enrichment results showed that these target genes play important roles in protein function and multiple pathways. In summary, we conducted bioinformatics and expression pattern studies on the PdMADS gene family and investigated six flowering samples from two almond cultivars, the early-flowering ‘Wanfeng’ and late-flowering ‘Nonpareil’, for quantitative expression level identification. These findings lay a foundation for future in-depth studies on the mechanism of PdMADS gene regulation during flowering in different almond cultivars.

From Floral Induction to Blooming: The Molecular Mysteries of Flowering in Woody Plants.

Flowering is a pivotal developmental process in response to the environment and determines the start of a new life cycle in plants. Woody plants usually possess a long juvenile nonflowering phase followed by an adult phase with repeated flowering cycles. The molecular mechanism underlying flowering regulation in woody plants is believed to be much more complex than that in annual herbs. In this review, we briefly describe the successive but distinct flowering processes in perennial trees, namely the vegetative phase change, the floral transition, floral organogenesis, and final blooming, and summarize in detail the most recent advances in understanding how woody plants regulate flowering through dynamic gene expression. Notably, the florigen gene FLOWERING LOCUS T(FT) and its antagonistic gene TERMINAL FLOWER 1 (TFL1) seem to play a central role in various flowering transition events. Flower development in different taxa requires interactions between floral homeotic genes together with AGL6 conferring floral organ identity. Finally, we illustrate the issues and corresponding measures of flowering regulation investigation. It is of great benefit to the future study of flowering in perennial trees.

OsFTL4, an FT-like Gene, Regulates Flowering Time and Drought Tolerance in Rice (Oryza sativa L.)

The initiation of flowering in cereals is a critical process influenced by environmental and endogenous signals. Flowering Locus T-like (FT-like) genes encode the main signals for flowering. Of the 13 FT-like genes in the rice genome, Hd3a/OsFTL2 and RFT1/OsFTL3 have been extensively studied and revealed to be critical for flowering. In this study, a rice FT-like gene, OsFTL4, was functionally characterized. Specifically, osftl4 mutants were generated using a CRISPR/Cas9 system. Compared with the wild-type control (Guangluai 4), the osftl4-1 and osftl4-2 mutants flowered 9.6 and 5.8 days earlier under natural long-day and short-day conditions, respectively. Additionally, OsFTL4 was mainly expressed in the vascular tissue, with the resulting OsFTL4 protein localized in both the nucleus and cytoplasm. Furthermore, OsFTL4 was observed to compete with Hd3a for the interaction with multiple 14-3-3 proteins. An analysis of the effects of simulated drought stress suggested that silencing OsFTL4 enhances drought tolerance by decreasing stomatal conductance and water loss. These results indicate that OsFTL4 helps integrate the flowering process and the drought response in rice.

AKR2A is involved in the flowering process of Arabidopsis thaliana

ABSTRACT Flowering at an appropriate time is crucial for plant development and reproduction. In Arabidopsis, the flowering process is managed by a regulatory network composed of at least 6 independent pathways. As a core protein in flowering regulation, FLOWERING LOCUS T (FT) participates in almost all these pathways. ANKYRIN REPEAT-CONTAINING PROTEIN 2A (AKR2A) was initially discovered as a 14-3-3-interacting protein. It was then found to be involved in the transportation of chloroplast outer membrane proteins and the resistance to low-temperature stress. Here, we identified an akr2a null mutant with a delayed flowering phenotype. Through the quantitative real-time PCR (qRT-PCR) and bimolecular fluorescence complementation (BiFC) assays, we demonstrated that AKR2A modulates the flowering process through its interaction with FT.

Foliar application of ethephon induces bud dormancy and affects gene expression of dormancy- and flowering-related genes in ‘Mauritius’ litchi (Litchi chinensis Sonn.)

A previous study showed that foliar application of ethephon to litchi trees with mature shoots and dormant terminal buds during autumn successfully inhibited new vegetative shoot growth prior to floral induction thereby promoting carbohydrate accumulation and flowering. However, the functional mechanisms of ethylene, the breakdown product of ethephon, in the leaves and terminal buds of litchi and its involvement in the flowering process is largely unknown. Therefore, this study aimed to investigate the phenological, physiological and molecular changes underlying ethephon application and its associations with bud dormancy and flowering in litchi. Ethephon was applied as a single full canopy spray at a concentration of 1000 mg⋅L−1 to ‘Mauritius’ litchi trees with mature vegetative shoots and dormant terminal buds during late autumn of 2018 (mid-April; Southern Hemisphere). Untreated trees served as a control. Phenological characteristics, such as bud dormancy and panicle development, leaf chlorophyll (as an indicator of shoot maturity), ethylene evolution, gene expression levels of flowering- (LcFT2, LcFLC and LcAP1), dormancy- (LcSVP1 and LcSVP2) and ethylene pathway-related (LcEIN3) genes and non-structural carbohydrates were determined in terminal buds, leaves and/or shoots. Ethephon application induced bud dormancy, significantly delayed panicle emergence and promoted pure floral panicle development under more favorable inductive conditions. Ethylene evolution increased sharply 2 h after application in both leaves and terminal buds, but decreased rapidly thereafter in the leaves, while remaining high in terminal buds for seven days before gradually declining. Ethephon application significantly increased relative expression of LcEIN3 and LcFLC in terminal buds one day after application, while LcFT2 expression in leaves and LcAP1 expression in terminal buds were significantly increased at the bud break stage. Significant treatments differences were also observed for various carbohydrate metabolites in leaves and shoots at the bud break or floral initiation stage. Our study provided evidence that ethephon application plays an important role in the physiological and molecular regulation of bud dormancy of litchi. By influencing the time of bud break, ethephon application can be a useful tool to manage panicle emergence under less inductive conditions.

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.

Ectopic expression of a bamboo SVP-like gene alters flowering time and floral organs in Arabidopsis thaliana

The Short Vegetative Phase (SVP) gene is a key regulator for floral transition and development. Although SVP-like genes have been identified and characterized in many plant species, their orthologs in bamboo have not been characterized. In this study, one SVP homolog was isolated from lei bamboo based on the P. edulis transcriptome database and designated as PvSVP2. Phylogenetic analysis showed that PvSVP2 was closely related to rice OsMADS47. Expression analysis revealed that PvSVP2 was widely expressed in different tissues but significantly in vegetative tissues. Moreover, it has higher transcript levels in the late stages of flower development. Overexpression of PvSVP2 in Arabidopsis thaliana caused the early flowering and abnormal floral morphologies. Further, the qRT-PCR analysis showed that the genes regulating flowering time (FT and SOC1) and flower development (AP1, AP3 and PI) expressions significantly increased in transgenic A. thaliana lines and correlated with PvSVP2 expression. The subcellular location of PvSVP2 in both onion epidermal cells and A. thaliana protoplast was localized in the nucleus and cytomembrane. Through yeast two-hybrid and BIFC assays, we identified that PvSVP2 interacts with PvMADS56 (a SOC1 homolog) and PvVRN1 (an AP1 homolog). These results suggested that PvSVP2 may play an essential role in the flowering process of bamboo by regulating the PvMADS56 and PvVRN1. Besides, we purified and obtained the PvSVP2 recombinant protein by prokaryotic inducement. Our data will provide information to understand the characterization and function of PvSVP2 and be beneficial to illustration the molecular mechanism of bamboo flowering.