Overexpression of Medicago SVP genes causes floral defects and delayed flowering in Arabidopsis but only affects floral development in Medicago

Gene-edited Mtsoc1 triple mutant Medicago plants do not flower

Optimized flowering time is an important trait that ensures successful plant adaptation and crop productivity. SOC1-like genes encode MADS transcription factors, which are known to play important roles in flowering control in many plants. This includes the best-characterized eudicot model Arabidopsis thaliana (Arabidopsis), where SOC1 promotes flowering and functions as a floral integrator gene integrating signals from different flowering-time regulatory pathways. Medicago truncatula (Medicago) is a temperate reference legume with strong genomic and genetic resources used to study flowering pathways in legumes. Interestingly, despite responding to similar floral-inductive cues of extended cold (vernalization) followed by warm long days (VLD), such as in winter annual Arabidopsis, Medicago lacks FLC and CO which are key regulators of flowering in Arabidopsis. Unlike Arabidopsis with one SOC1 gene, multiple gene duplication events have given rise to three MtSOC1 paralogs within the Medicago genus in legumes: one Fabaceae group A SOC1 gene, MtSOC1a, and two tandemly repeated Fabaceae group B SOC1 genes, MtSOC1b and MtSOC1c. Previously, we showed that MtSOC1a has unique functions in floral promotion in Medicago. The Mtsoc1a Tnt1 retroelement insertion single mutant showed moderately delayed flowering in long- and short-day photoperiods, with and without prior vernalization, compared to the wild-type. In contrast, Mtsoc1b Tnt1 single mutants did not have altered flowering time or flower development, indicating that it was redundant in an otherwise wild-type background. Here, we describe the generation of Mtsoc1a Mtsoc1b Mtsoc1c triple mutant lines using CRISPR-Cas9 gene editing. We studied two independent triple mutant lines that segregated plants that did not flower and were bushy under floral inductive VLD. Genotyping indicated that these non-flowering plants were homozygous for the predicted strong mutant alleles of the three MtSOC1 genes. Gene expression analyses using RNA-seq and RT-qPCR indicated that these plants remained vegetative. Overall, the non-flowering triple mutants were dramatically different from the single Mtsoc1a mutant and the Arabidopsis soc1 mutant; implicating multiple MtSOC1 genes in critical overlapping roles in the transition to flowering in Medicago.

Functional analysis of a lily SHORT VEGETATIVE PHASE ortholog in flowering transition and floral development

Lilium is a commercially important genus of bulbous flowers, investigating the flowering molecular mechanisms is important for flowering regulation of lily. MADS-box SHORT VEGETATIVE PHASE (SVP) orthologs are involved in the flowering transition and floral organ differentiation in many plants. In this study, we identified an SVP ortholog from L. × formolongi (LfSVP), which was closely related to Arabidopsis SVP according to phylogenetic analysis. Tissue-specific expression patterns indicated that LfSVP expression levels peaked in the leaves and showed low expression levels in flowering tepals. Stage-dependent expression patterns of LfSVP showed high transcription level in the flowering induction stage under different photoperiods and exhibited transcription peak in the floral budding development stage under long days. Overexpressed LfSVP led to delayed flowering and floral organ defects in Arabidopsis independent of photoperiod. Tobacco rattle virus -induced gene silencing of LfSVP caused a strongly earlier flowering time and floral organ defects of L. × formolongi. Moreover, LfSVP can interact with L. × formolongi APETALA1 (AP1) in both yeast and tobacco cells, and the two may interact to regulate floral organ differentiation. In conclusion, LfSVP is a flowering repressor and may be involved in the regulation of floral organ differentiation. This study will be helpful for the molecular breeding of short-life-period and rich floral patterns lily varieties.

Modeling the Flowering Activation Motif during Vernalization in Legumes: A Case Study of M. trancatula

In many plant species, flowering is promoted by the cold treatment or vernalization. The mechanism of vernalization-induced flowering has been extensively studied in Arabidopsis but remains largely unknown in legumes. The orthologs of the FLC gene, a major regulator of vernalization response in Arabidopsis, are absent or non-functional in the vernalization-sensitive legume species. Nevertheless, the legume integrator genes FT and SOC1 are involved in the transition of the vernalization signal to meristem identity genes, including PIM (AP1 ortholog). However, the regulatory contribution of these genes to PIM activation in legumes remains elusive. Here, we presented the theoretical and data-driven analyses of a feed-forward regulatory motif that includes a vernalization-responsive FT gene and several SOC1 genes, which independently activate PIM and thereby mediate floral transition. Our theoretical model showed that the multiple regulatory branches in this regulatory motif facilitated the elimination of no-sense signals and amplified useful signals from the upstream regulator. We further developed and analyzed four data-driven models of PIM activation in Medicago trancatula in vernalized and non-vernalized conditions in wild-type and fta1-1 mutants. The model with FTa1 providing both direct activation and indirect activation via three intermediate activators, SOC1a, SOC1b, and SOC1c, resulted in the most relevant PIM dynamics. In this model, the difference between regulatory inputs of SOC1 genes was nonessential. As a result, in the M. trancatula model, the cumulative action of SOC1a, SOC1b, and SOC1c was favored. Overall, in this study, we first presented the in silico analysis of vernalization-induced flowering in legumes. The considered vernalization network motif can be supplemented with additional regulatory branches as new experimental data become available.

Comparative transcriptomic analysis reveals differences in MADS-box genes of different hypericum in Changbai Mountains

To explore the differences between the hypericum in the Changbai Mountains, we carried out a transcriptome analysis of two common hypericums in the area, which was Hypericum attenuatum Choisy and Hypericum longistylum Oliv. We screened the MADS-box genes to analyze divergence time and evolutionary selection expression, and determine their expression levels. The results showed that we detected 9287 differentially expressed genes in the two species, of which shared 6044 genes by the two species. Analysis of the selected MADS genes revealed that the species was in an environment adapted to its natural evolution. The divergence time estimation showed that the segregation of these genes in the two species was related to the changes of external environment and genome replication events. The results of relative expression showed that the later flowering period of Hypericum attenuatum Choisy was related to the higher expression of the SVP (SHORT VEGETATIVE PHASE) and the AGL12 (AGAMOUS LIKE 12), while the lower expression of the FUL (FRUITFULL).

Functional characterization of two flowering repressors SHORT VEGETATIVE PHASE and TERMINAL FLOWER 1 in reblooming bearded Iris (Iris spp.)

Reblooming bearded iris (Iris spp.) could bloom in both spring and autumn, which has extended the ornamental periods. Our previous transcriptome analysis has indicated the possible regulatory role of SHORT VEGETATIVE PHASE (SVP) in reblooming of bearded iris. Moreover, it has been revealed that the mutations of TERMINAL FLOWER 1 (TFL1) led to the continuous-flowering phenotypes in rose (Rosa spp.) and strawberry (Fragaria spp.). In order to verify the functions of these two genes on reblooming in bearded iris, IgSVP and IgTFL1 were isolated and functionally characterized. All the overexpression Arabidopsis lines of IgSVP and IgTFL1 generated the late-flowering phenotypes, indicating their functions as flowering repressors. The ectopic expression of IgSVP and IgTFL1 also generated phenotypic changes on flowers, inflorescences and branch structures. Moreover, the protein-protein interaction was found between a homologue of IgSVP and the floral meristem identity gene APETALA 1. The expression profiling showed that IgSVP was expressed significantly lower in the rebloomers in the second floral initiation stage (T5) than those of the first one (T1) in both the once-bloomers and the rebloomers, suggesting the possible regulation of IgSVP on reblooming. However, the expression level of IgTFL1 in the rebloomers was significantly higher in T5 than that in T1. The functional characterization of the two important flowering repressors IgSVP and IgTFL1 could lay solid foundation for future molecular breeding of iris, for example, knocking out the key repressors by CRISPR/Cas9 system to extend the ornamental periods of bearded iris.

IiSVP of Isatis indigotica can reduce the size and repress the development of floral organs

IiSVP of Isatis indigotica was cloned and its expression pattern was analyzed. Ectopic expression of IiSVP in Arabidopsis could delay the flowering time and reduce the size of the floral organs. SVP (SHORT VEGETATIVE PHASE) can negatively regulate the flowering time of Arabidopsis. In the present work, the cDNA of IiSVP, an orthologous gene of AtSVP in I. indigotica, was cloned. IiSVP was highly expressed in rosette leaves, inflorescences and petals, but weakly expressed in sepals, pistils and young silicles. The results of subcellular localization showed that IiSVP was localized in nucleus. Bioinformatics analysis indicated that this protein was a MADS-box transcription factor. Constitutive expression of IiSVP in Arabidopsis thaliana resulted in decrease of the number of petals and stamens, and curly sepals were formed. In IiSVP transgenic Arabidopsis plants, obvious phenotypic variations in flowers could be observed, especially the size of the floral organs. In comparison with the wild-type plants, the size of petals, stamens and pistil in IiSVP transgenic Arabidopsis plants was decreased significantly. In some transgenic plants, the petals were wrapped by the sepals. Yeast two-hybrid experiments showed that IiSVP could form higher-order complexes with other MADS proteins, including IiSEP1, IiSEP3, IiAP1 and IiSEP4, but could not interact with IiSEP2. In this work, it was proved that the flowering process and the floral development in Arabidopsis could be affected by IiSVP from I. indigotica Fortune.

Overexpression of <italic>PvSVP1</italic>, an <italic>SVP</italic>-like gene of bamboo, causes early flowering and abnormal floral organs in <italic>Arabidopsis</italic> and rice

<p indent="0mm">Bamboo is a nontimber woody plant featuring a long vegetative stage and uncertain flowering time. Therefore, the genes belonging to flowering repressors might be essential in regulating the transition from the vegetative to reproductive stage in bamboo. The <italic>Short Vegetative Phase</italic> ( <italic>SVP</italic>) gene plays a pivotal role in floral transition and development. However, little is known about the bamboo <italic>SVP</italic> homologues. In this study, <italic>Phyllostachys violascens</italic> <italic>PvSVP1</italic> is isolated by analysis of the <italic>P</italic>. <italic>edulis</italic> transcriptome database. Phylogenetic analysis shows that <italic>PvSVP1</italic> is closely related to <italic>OsMADS55</italic> (rice <italic>SVP</italic> homolog). <italic>PvSVP1</italic> is ubiquitously expressed in various tissues, predominantly in vegetative tissues. To investigate the function of <italic>PvSVP1</italic>, <italic>PvSVP1</italic> is overexpressed in <italic>Arabidopsis</italic> and rice under the influence of the 35S promoter. Overexpression of <italic>PvSVP1</italic> in <italic>Arabidopsis</italic> causes early flowering and produces abnormal petals and sepals. Quantitative real-time PCR reveals that overexpression in <italic>Arabidopsis</italic> produces an early flowering phenotype by downregulating <italic>FLC</italic> and upregulating <italic>FT</italic> and produces abnormal floral organs by upregulating <italic>AP1</italic>, <italic>AP3</italic> and <italic>PI</italic> expressions. Simultaneously, overexpression of <italic>PvSVP1</italic> in rice alters the expressions of flowering-related genes such as <italic>Hd3a</italic>, <italic>RFT1</italic>, <italic>OsMADS56</italic> and <italic>Ghd7</italic> and promotes flowering under field conditions. In addition, PvSVP1 may be a nuclear protein which interacts with PvVRN1 and PvMADS56 on the yeast two-hybrid and BiFC systems. Our study suggests that <italic>PvSVP1</italic> may play a vital role in flowering time and development by interacting with PvVRN1 and PvMADS56 in the nucleus. Furthermore, this study paves the way toward understanding the complex flowering process of bamboo. </p>.

Transcriptomic analysis reveals the formation mechanism of anemone-type flower in chrysanthemum

BACKGROUND

The ray and disc florets on the chrysanthemum capitulum are morphologically diverse and have remarkably abundant variant types, resulting in a rich variety of flower types. An anemone shape with pigmented and elongated disk florets is an important trait in flower shape breeding of chrysanthemums. The regulatory mechanism of their anemone-type disc floret formation was not clear, thus limiting the directional breeding of chrysanthemum flower types. In this study, we used morphological observation, transcriptomic analysis, and gene expression to investigate the morphogenetic processes and regulatory mechanisms of anemone-type chrysanthemum.

RESULT

Scanning electron microscopy (SEM) observation showed that morphological differences between non-anemone-type disc florets and anemone-type disc florets occurred mainly during the petal elongation period. The anemone-type disc florets elongated rapidly in the later stages of development. Longitudinal paraffin section analysis revealed that the anemone-type disc florets were formed by a great number of cells in the middle layer of the petals with vigorous division. We investigated the differentially expressed genes (DEGs) using ray and disc florets of two chrysanthemum cultivars, 082 and 068, for RNA-Seq and their expression patterns of non-anemone-type and anemone-type disc florets. The result suggested that the CYCLOIDEA2 (CYC2s), MADS-box genes, and phytohormone signal-related genes appeared significantly different in both types of disc florets and might have important effects on the formation of anemone-type disc florets. In addition, it is noteworthy that the auxin and jasmonate signaling pathways might play a vital role in developing anemone-type disc florets.

CONCLUSIONS

Based on our findings, we propose a regulatory network for forming non-anemone-type and anemone-type disc florets. The results of this study lead the way to further clarify the mechanism of the anemone-type chrysanthemum formation and lay the foundation for the directive breeding of chrysanthemum petal types.

MtING2 encodes an ING domain PHD finger protein which affects Medicago growth, flowering, global patterns of H3K4me3, and gene expression

Flowering of the reference legume Medicago truncatula is promoted by winter cold (vernalization) followed by long-day photoperiods (VLD) similar to winter annual Arabidopsis. However, Medicago lacks FLC and CO, key regulators of Arabidopsis VLD flowering. Most plants have two INHIBITOR OF GROWTH (ING) genes (ING1 and ING2), encoding proteins with an ING domain with two anti-parallel alpha-helices and a plant homeodomain (PHD) finger, but their genetic role has not been previously described. In Medicago, Mting1 gene-edited mutants developed and flowered normally, but an Mting2-1 Tnt1 insertion mutant and gene-edited Mting2 mutants had developmental abnormalities including delayed flowering particularly in VLD, compact architecture, abnormal leaves with extra leaflets but no trichomes, and smaller seeds and barrels. Mting2 mutants had reduced expression of activators of flowering, including the FT-like gene MtFTa1, and increased expression of the candidate repressor MtTFL1c, consistent with the delayed flowering of the mutant. MtING2 overexpression complemented Mting2-1, but did not accelerate flowering in wild type. The MtING2 PHD finger bound H3K4me2/3 peptides weakly in vitro, but analysis of gene-edited mutants indicated that it was dispensable to MtING2 function in wild-type plants. RNA sequencing experiments indicated that >7000 genes are mis-expressed in the Mting2-1 mutant, consistent with its strong mutant phenotypes. Interestingly, ChIP-seq analysis identified >5000 novel H3K4me3 locations in the genome of Mting2-1 mutants compared to wild type R108. Overall, our mutant study has uncovered an important physiological role of a plant ING2 gene in development, flowering, and gene expression, which likely involves an epigenetic mechanism.

Mechanisms of Vernalization-Induced Flowering in Legumes

Vernalization is the requirement for exposure to low temperatures to trigger flowering. The best knowledge about the mechanisms of vernalization response has been accumulated for Arabidopsis and cereals. In Arabidopsis thaliana, vernalization involves an epigenetic silencing of the MADS-box gene FLOWERING LOCUS C (FLC), which is a flowering repressor. FLC silencing releases the expression of the main flowering inductor FLOWERING LOCUS T (FT), resulting in a floral transition. Remarkably, no FLC homologues have been identified in the vernalization-responsive legumes, and the mechanisms of cold-mediated transition to flowering in these species remain elusive. Nevertheless, legume FT genes have been shown to retain the function of the main vernalization signal integrators. Unlike Arabidopsis, legumes have three subclades of FT genes, which demonstrate distinct patterns of regulation with respect to environmental cues and tissue specificity. This implies complex mechanisms of vernalization signal propagation in the flowering network, that remain largely elusive. Here, for the first time, we summarize the available information on the genetic basis of cold-induced flowering in legumes with a special focus on the role of FT genes.

Integrative Analyses of Transcriptomes and Metabolomes Reveal Associated Genes and Metabolites with Flowering Regulation in Common Vetch (Vicia sativa L.)

As an important source of protein for livestock and human consumption, Vicia sativa is cultivated worldwide, but its seed production is hampered at high altitudes because of the short frost-free period. Flowering represents the transition from a vegetative to a reproductive period, and early flowering benefits plant seed production at high altitudes. However, the molecular mechanisms of flowering regulation in V. sativa remain elusive. In the present study, two V. sativa accessions with different flowering characteristics were used: Lan3 (early-flowering) was cultivated by our laboratory, and 503 (late-flowering) was selected from 222 V. sativa accessions after three years of field experiments. The shoot samples (shoot tip length = 10 cm) of these two accessions were collected 63, 70, and 77 days after sowing, and the molecular regulatory mechanism of the flowering process was identified by integrative analyses of the transcriptomes and metabolomes. Kyoto Encyclopedia of Genes and Genomes enrichment showed that the synthesis and signal transduction of plant hormone pathways were the most enriched pathways in 4274 differentially expressed genes (DEGs) and in 259 differential metabolites between Lan3 and 503. Moreover, the contents of three metabolites related to salicylic acid biosynthesis and the transcription levels of two DEGs related to salicylic acid signal transduction in Lan3 were higher than those in 503. Further verification in various accessions indicated that salicylic acid metabolism may be involved in the flowering regulation process of V. sativa. These findings provide valuable information for understanding the flowering mechanism and for promoting breeding research in V. sativa.

Characterization of Phytohormones and Transcriptomic Profiling of the Female and Male Inflorescence Development in Manchurian Walnut (Juglans mandshurica Maxim.)

Flowers are imperative reproductive organs and play a key role in the propagation of offspring, along with the generation of several metabolic products in flowering plants. In Juglans mandshurica, the number and development of flowers directly affect the fruit yield and subsequently its commercial value. However, owing to the lack of genetic information, there are few studies on the reproductive biology of Juglans mandshurica, and the molecular regulatory mechanisms underlying the development of female and male inflorescence remain unclear. In this study, phytohormones and transcriptomic sequencing analyses at the three stages of female and male inflorescence growth were performed to understand the regulatory functions underlying flower development. Gibberellin is the most dominant phytohormone that regulates flower development. In total, 14,579 and 7188 differentially expressed genes were identified after analyzing the development of male and female flowers, respectively, wherein, 3241 were commonly expressed. Enrichment analysis for significantly enriched pathways suggested the roles of MAPK signaling, phytohormone signal transduction, and sugar metabolism. Genes involved in floral organ transition and flowering were obtained and analyzed; these mainly belonged to the M-type MADS-box gene family. Three flowering-related genes (SOC1/AGL20, ANT, and SVP) strongly interacted with transcription factors in the co-expression network. Two key CO genes (CO3 and CO1) were identified in the photoperiod pathway. We also identified two GA20xs genes, one SVP gene, and five AGL genes (AGL8, AGL9, AGL15, AGL19, and AGL42) that contributed to flower development. The findings are expected to provide a genetic basis for the studies on the regulatory networks and reproductive biology in inflorescence development for J. mandshurica.

Identification and Characterization of the MIKC-Type MADS-Box Gene Family in Brassica napus and Its Role in Floral Transition

Increasing rapeseed yield has always been a primary goal of rapeseed research and breeding. However, flowering time is a prerequisite for stable rapeseed yield and determines its adaptability to ecological regions. MIKC-type MADS-box (MICK) genes are a class of transcription factors that are involved in various physiological and developmental processes in plants. To understand their role in floral transition-related pathways, a genome-wide screening was conducted with Brassica napus (B. napus), which revealed 172 members. Using previous data from a genome-wide association analysis of flowering traits, BnaSVP and BnaSEP1 were identified as candidate flowering genes. Therefore, we used the CRISPR/Cas9 system to verify the function of BnaSVP and BnaSEP1 in B. napus. T0 plants were edited efficiently at the BnaSVP and BnaSEP1 target sites to generate homozygous and heterozygous mutants with most mutations stably inherited by the next generation. Notably, the mutant only showed the early flowering phenotype when all homologous copies of BnaSVP were edited, indicating functional redundancy between homologous copies. However, no changes in flowering were observed in the BnaSEP1 mutant. Quantitative analysis of the pathway-related genes in the BnaSVP mutant revealed the upregulation of SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FLOWERING LOCUS T (FT) genes, which promoted early flowering in the mutant. In summary, our study created early flowering mutants, which provided valuable resources for early maturing breeding, and provided a new method for improving polyploid crops.

Flowering process in soybean under water deficit conditions: A review on genetic aspects

Soybean is a key crop in many countries, being used from human food to the animal industry due to its nutritional properties. Financially, the grain chain moves large sums of money into the economy of producing countries. However, like other agricultural commodities around the world, it can have its final yield seriously compromised by abiotic environmental stressors, like drought. As flowers imply in pods and in grains inside it to minimize damages caused by water restriction, researchers have focused on understanding flowering-process related genes and their interactions. Here a review dedicated to the soybean flowering process and gene network involved in it is presented, describing gene interactions and how genes act in this complex mechanism, also ruled by environmental triggers such as day-light and circadian cycle. The objective was to gather information and insights on the soybean flowering process, aiming to provide knowledge useful to assist in the development of drought-tolerant soybean lines, minimizing losses due to delays or anticipation of flowering and, consequently, restraining financial and productivity losses.

Molecular Characterization and Expression Patterns of the HkSVP Gene Reveal Distinct Roles in Inflorescence Structure and Floral Organ Development in Hemerocallis fulva

SHORT VEGETATIVE PHASE (SVP) genes are members of the well-known MADS-box gene family that play a key role in regulating vital developmental processes in plants. Hemerocallis are perennial herbs that exhibit continuous flowering development and have been extensively used in landscaping. However, there are few reports on the regulatory mechanism of flowering in Hemerocallis. To better understand the molecular basis of floral formation of Hemerocallis, we identified and characterized the SVP-like gene HkSVP from the Hemerocallis cultivar 'Kanai Sensei'. Quantitative RT-PCR (qRT-PCR) indicated that HkSVP transcript was mainly expressed in the vegetative growth stage and had the highest expression in leaves, low expression in petals, pedicels and fruits, and no expression in pistils. The HkSVP encoded protein was localized in the nucleus of Arabidopsis protoplasts and the nucleus of onion epidermal cells. Yeast two hybrid assay revealed that HKSVP interacted with Hemerocallis AP1 and TFL1. Moreover, overexpression of HkSVP in Arabidopsis resulted in delayed flowering and abnormal phenotypes, including enriched trichomes, increased basal inflorescence branches and inhibition of inflorescence formation. These observations suggest that the HkSVP gene may play an important role in maintaining vegetative growth by participating in the construction of inflorescence structure and the development of flower organs.

A novel Medicago truncatula calmodulin-like protein (MtCML42) regulates cold tolerance and flowering time

Calmodulin-like proteins (CMLs) are one of the Ca²⁺ sensors in plants, but the functions of most CMLs remain unknown. The regulation of cold tolerance and flowering time by MtCML42 in Medicago truncatula and the underlying mechanisms were investigated using MtCML42-overexpressing plants and cml42 Medicago mutants with a Tnt1 retrotransposon insertion. Compared with the wild type (WT), MtCML42-overexpressing lines had increased cold tolerance, whereas cml42 mutants showed decreased cold tolerance. The impaired cold tolerance in cml42 could b complemented by MtCML42 expression. The transcript levels of MtCBF1, MtCBF4, MtCOR413, MtCAS15, MtLTI6A, MtGolS1 and MtGolS2 and the concentrations of raffinose and sucrose were increased in response to cold treatment, whereas higher levels were observed in MtCML42-overexpressing lines and lower levels were observed in cml42 mutants. In addition, early flowering with upregulated MtFTa1 and downregulated MtABI5 transcripts was observed in MtCML42-overexpressing lines, whereas delayed flowering with downregulated MtFTa1 and upregulated MtABI5 was observed in cml42. MtABI5 expression could complement the flowering phenotype in the Arabidopsis mutant abi5. Our results suggest that MtCML42 positively regulates MtCBF1 and MtCBF4 expression, which in turn upregulates the expression of some COR genes, MtGolS1 and MtGolS2, which leads to raffinose accumulation and increased cold tolerance. MtCML42 regulates flowering time through sequentially downregulating MtABI5 and upregulating MtFTa1 expression.

Isolation and Functional Characterization of Two SHORT VEGETATIVE PHASE Homologous Genes from Mango

The SHORT VEGETATIVE PHASE (SVP) gene is a transcription factor that integrates flowering signals and plays an important role in the regulation of flowering time in many plants. In this study, two full-length cDNA sequences of SVP homologous genes—MiSVP1 and MiSVP2—were obtained from ‘SiJiMi’ mango. Sequence analysis showed that the MiSVPs had typical MADS-box domains and were highly conserved between each other. The analysis of expression patterns showed that the MiSVPs were expressed during flower development and highly expressed in vegetative tissues, with low expression in flowers/buds. The MiSVPs could responded to low temperature, NaCl, and PEG treatment. Subcellular localization revealed that MiSVP1 and MiSVP2 were localized in the nucleus. Transformation of Arabidopsis revealed that overexpression of MiSVP1 delayed flowering time, overexpression of MiSVP2 accelerated flowering time, and neither MiSVP1 nor MiSVP2 had an effect on the number of rosette leaves. Overexpression of MiSVP1 increased the expression of AtFLC and decreased the expression of AtFT and AtSOC1, and overexpression of MiSVP2 increased the expression levels of AtSOC1 and AtFT and decreased the expression levels of AtFLC. Point-to-point and bimolecular fluorescence complementation (BiFC) assays showed that MiSVP1 and MiSVP2 could interact with SEP1-1, SOC1D, and AP1-2. These results suggest that MiSVP1 and MiSVP2 may play a significant roles in the flowering process of mango.

Genetic regulation of flowering time and inflorescence architecture by MtFDa and MtFTa1 in Medicago truncatula

Regulation of floral transition and inflorescence development is crucial for plant reproductive success. FLOWERING LOCUS T (FT) is one of the central players in the flowering genetic regulatory network, whereas FLOWERING LOCUS D (FD), an interactor of FT and TERMINAL FLOWER 1 (TFL1), plays significant roles in both floral transition and inflorescence development. Here we show the genetic regulatory networks of floral transition and inflorescence development in Medicago truncatula by characterizing MtFTa1 and MtFDa and their genetic interactions with key inflorescence meristem (IM) regulators. Both MtFTa1 and MtFDa promote flowering; the double mutant mtfda mtfta1 does not proceed to floral transition. RNAseq analysis reveals that a broad range of genes involved in flowering regulation and flower development are up- or downregulated by MtFTa1 and/or MtFDa mutations. Furthermore, mutation of MtFDa also affects the inflorescence architecture. Genetic analyses of MtFDa, MtFTa1, MtTFL1, and MtFULc show that MtFDa is epistatic to MtFULc and MtTFL1 in controlling IM identity. Our results demonstrate that MtFTa1 and MtFDa are major flowering regulators in M. truncatula, and MtFDa is essential both in floral transition and secondary inflorescence development. The study will advance our understanding of the genetic regulation of flowering time and inflorescence development in legumes.

SVP-like gene PavSVP potentially suppressing flowering with PavSEP, PavAP1, and PavJONITLESS in sweet cherries (Prunus avium L.)

The MADS-box transcription factor SHORT VEGETATIVE PHASE (SVP) gene have important functions in flowering and dormancy regulation. However, the molecular mechanism of PavSVP regulating flowering and dormancy in sweet cherry remains unknown. We identified a MADS-box gene SVP-like named PavSVP from sweet cherry, which was closely to PmSVP and PpSVP from Prunus mume and Prunus persica by using phylogenetic tree analysis, suggesting a conserved function with these evolutionarily closer SVP homologs. Subcellular localization analysis indicated that, PavSVP was localized in the nucleus and cytomembrane. PavSVP expression in sweet cherries were observed in vegetative and floral tissues, but much higher level in flower buds. The seasonal expression level of PavSVP was higher during the stage of summer growth in flower buds, and declined gradually toward dormancy and flower initiation. Ectopic expression of PavSVP induced a delayed flowering and the occurrence of abnormal flowers, including curly sepals and plicated siliques in Arabidopsis. Furthermore, protein interaction analysis showed that PavSVP interacted with PavSEP, PavAP1 and PavJONITLESS. Unlike PavSVP, over-expression of PavSEP in Arabidopsis caused early flowering phenotype. In addition, the expression of PavSEP in flower buds was low in summer. These results will help reveal the molecular mechanisms of PavSVP in maintaining the suppression phase of flowering in sweet cherry during summer and winter.

MtFULc controls inflorescence development by directly repressing MtTFL1 in Medicago truncatula

Flowering plants display a vast diversity of inflorescence architecture, which plays an important role in determining seed yield and fruit production. Unlike the model eudicot Arabidopsis thaliana that has simple inflorescences, most legume plants have compound types of inflorescences. Recent studies in the model legume species Pisum sativum and Medicago truncatula showed that the MADS-box transcription factors VEGETATIVE1/PsFRUITFULc/MtFRUITFULc (VEG1/PsFULc and MtFULc) are essential for the development of compound inflorescences by specifying the secondary inflorescence meristem identity. In this study, we report the isolation and characterization of two new mtfulc alleles by screening the M. truncatula Tnt1 insertion mutant collection. We found that MtFULc specifies M. truncatula secondary inflorescence meristem identity in a dose-dependent manner. Biochemical analysis and chromatin immunoprecipitation (ChIP) assays revealed that MtFULc acts as a transcriptional repressor to directly repress the expression of MtTFL1 through its promoter and 3' intergenic region. Comprehensive genetic analysis suggest MtFULc coordinates with the primary inflorescence meristem maintainer MtTFL1 and floral meristem regulator MtPIM to control M. truncatula inflorescence development. Our findings help to elucidate the mechanism of MtFULc-mediated regulation of secondary inflorescence meristem identity and provide insights into understanding the genetic regulatory network underlying compound inflorescence development in legumes.

Unisexual flower initiation in the monoecious Quercus suber L.: a molecular approach

Several plant species display a temporal separation of the male and female flower organ development to enhance outbreeding; however, little is known regarding the genetic mechanisms controlling this temporal separation. Quercus suber is a monoecious oak tree with accentuated protandry: in late winter, unisexual male flowers emerge adjacent to the swollen buds, whereas unisexual female flowers emerge in the axils of newly formed leaves formed during spring (4-8 weeks after male flowering). Here, a phylogenetic profiling has led to the identification of cork oak homologs of key floral regulatory genes. The role of these cork oak homologs during flower development was identified with functional studies in Arabidopsis thaliana. The expression profile throughout the year of flower regulators (inducers and repressors), in leaves and buds, suggests that the development of male and female flowers may be preceded by separated induction events. Female flowers are most likely induced during the vegetative flush occurring in spring, whereas male flowers may be induced in early summer. Male flowers stay enclosed within the pre-dormant buds, but complete their development before the vegetative flush of the following year, displaying a long period of anthesis that spans the dormant period. Our results portray a genetic mechanism that may explain similar reproductive habits in other monoecious tree species.

Medicago PHYA promotes flowering, primary stem elongation and expression of flowering time genes in long days

BACKGROUND

Flowering time is an important trait for productivity in legumes, which include many food and fodder plants. Medicago truncatula (Medicago) is a model temperate legume used to study flowering time pathways. Like Arabidopsis thaliana (Arabidopsis), its flowering is promoted by extended periods of cold (vernalization, V), followed by warm long day (LD) photoperiods. However, Arabidopsis flowering-time genes such as the FLOWERING LOCUS C (FLC)/ MADS AFFECTING FLOWERING (MAF) clade are missing and CONSTANS-LIKE (CO-LIKE) genes do not appear to have a role in Medicago or Pisum sativum (pea). Another photoperiodic regulator, the red/far red photoreceptor PHYTOCHROME A (PHYA), promotes Arabidopsis flowering by stabilizing the CO protein in LD. Interestingly, despite the absence of CO-LIKE function in pea, PsPHYA plays a key role in promoting LD photoperiodic flowering and plant architecture. Medicago has one homolog of PHYA, MtPHYA, but its function is not known.

RESULTS

Genetic analysis of two MtPHYA Tnt1 insertion mutant alleles indicates that MtPHYA has an important role in promoting Medicago flowering and primary stem elongation in VLD and LD and in perception of far-red wavelengths in seedlings. MtPHYA positively regulates the expression of MtE1-like (MtE1L), a homologue of an important legume-specific flowering time gene, E1 in soybean and other Medicago LD-regulated flowering-time gene homologues, including the three FLOWERING LOCUS T-LIKE (FT-LIKE) genes, MtFTa1, MtFTb1 and MtFTb2 and the two FRUITFULL-LIKE (FUL-LIKE) genes MtFULa and MtFULb. MtPHYA also modulates the expression of the circadian clock genes, GIGANTEA (GI) and TIMING OF CAB EXPRESSION 1a (TOC1a). Genetic analyses indicate that Mtphya-1 Mte1l double mutants flowered at the same time as the single mutants. However, Mtphya-1 Mtfta1 double mutants had a weak additive effect in delaying flowering and in reduction of primary axis lengths beyond what was conferred by either of the single mutants.

CONCLUSION

MtPHYA has an important role in LD photoperiodic control of flowering, plant architecture and seedling de-etiolation under far-red wavelengths in Medicago. It promotes the expression of LD-induced flowering time genes and modulates clock-related genes. In addition to MtFTa1, MtPHYA likely regulates other targets during LD floral induction in Medicago.

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

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

Cloning and functional characterization of a floral repressor gene from Lavandula angustifolia

Using RNA-Seq, we identified genes involved in floral development in lavenders and functionally characterized the floral repressor LaSVP. The molecular aspects of flower initiation and development have not been adequately investigated in lavender (Lavandula). In order to identify genes that control these processes, we employed RNA-Seq to obtain sequence information for transcripts originating from the vegetative shoot apical meristem (SAM) and developing inflorescence tissues of Lavandula angustifolia and Lavandula × intermedia plants, and assemble a comprehensive transcriptome of 105,294 contigs. Homology-based annotation provided gene ontology terms for the majority of transcripts, including over 100 genes homologous to those that control flower initiation and organ identity in Arabidopsis thaliana. Expression analysis revealed that most of these genes are differentially expressed during flower development. For example, LaSVP, a homolog of the floral repressor SHORT VEGETATIVE PHASE (SVP), was strongly expressed in vegetative SAM compared to developing flowers, implicating its potential involvement in flowering repression in lavender. To investigate LaSVP further, we constitutively expressed the gene in transformed A. thaliana plants, evaluating its effects on flower initiation and morphology. Expression of the LaSVP in A. thaliana delayed flowering and affected flower organ identity in a dosage-dependent manner. Two of the highest expressing lines produced sepals instead of petals and were sterile as they failed to develop proper seed pods. This study provides the foundation for future investigations aimed at elucidating flower initiation and development in lavender.

Expansion and Functional Divergence of the SHORT VEGETATIVE PHASE (SVP) Genes in Eudicots

SHORT VEGETATIVE PHASE (SVP) genes are members of the well-known MADS-box gene family that regulates vital developmental processes in plants. In Arabidopsis, there are two SVP paralogs, SVP/AGAMOUS-LIKE22 (SVP/AGL22) and AGL24. SVP protein suppresses the flowering process, whereas AGL24 acts as a flowering activator. Phylogenetic analysis of SVP genes representing most of the sequenced eudicot species showed that the SVP gene family could be divided into three major clades in eudicots (SVP1, SVP2, and SVP3), most likely resulting from an ancient whole-genome triplication in core eudicots. Among them, the SVP1 (SVP) and SVP2 (AGL24) clades are retained in nearly all species, whereas the SVP3 clade has been lost in Brassicaceae, Myrtaceae, and some species in other families. Reflecting lineage-specific tandem duplication and whole-genome duplication, SVP gene copy numbers ranged from 3 to 11 in the analyzed species. Sequence analysis showed that SVP3 proteins have obvious differences with SVP1 and SVP2 in the C-terminal (C) domain and intervening (I) domain. Positive selection analysis also showed that the ω (dN/dS) value was highest in the SVP3 clade, with 17 positive selection sites detected in the SVP3 clade. Promoter analysis for cis-regulatory elements showed that some genes in the SVP2 and SVP3 clades may be regulated by abscisic acid, ethylene, and gibberellin. RNA-seq data from grape, poplar, and apple revealed that genes in SVP3 group are highly expressed in vegetative organs such as buds, leaves, cotyledons, and dormant buds in particular, indicating the involvement of genes belong to SVP3 group in the dormancy process. Overall, the findings underscore the functional diversity of the SVP genes in eudicots.

A SOC1-like gene MtSOC1a promotes flowering and primary stem elongation in Medicago

Medicago flowering, like that of Arabidopsis, is promoted by vernalization and long days, but alternative mechanisms are predicted because Medicago lacks the key regulators CO and FLC. Three Medicago SOC1-like genes, including MtSOC1a, were previously implicated in flowering control, but no legume soc1 mutants with altered flowering were reported. Here, reverse transciption-quantitative PCR (RT-qPCR) indicated that the timing and magnitude of MtSOC1a expression was regulated by the flowering promoter FTa1, while in situ hybridization indicated that MtSOC1a expression increased in the shoot apical meristem during the floral transition. A Mtsoc1a mutant showed delayed flowering and short primary stems. Overexpression of MtSOC1a partially rescued the flowering of Mtsoc1a, but caused a dramatic increase in primary stem height, well before the transition to flowering. Internode cell length correlated with stem height, indicating that MtSOC1a promotes cell elongation in the primary stem. However, application of gibberellin (GA3) caused stem elongation in both the wild type and Mtsoc1a, indicating that the mutant was not defective in gibberellin responsiveness. These results indicate that MtSOC1a may function as a floral integrator gene and promotes primary stem elongation. Overall, this study suggests that apart from some conservation with the Arabidopsis flowering network, MtSOC1a has a novel role in regulating aspects of shoot architecture.

Functional Genomics and Flowering Time in Medicago truncatula: An Overview

Flowering time is an important trait that influences adaptation and yield in many crop legumes. Both the inherent earliness of flowering and the degree to which it is responsive to environmental factors determine both the eco-geographic range across which crops can be successfully grown and the seasonal cycles most suitable for production. This chapter will provide a brief review of studies investigating the genetic control of flowering time in Medicago truncatula.

The development of functional mapping by three sex-related loci on the third whorl of different sex types of Carica papaya L

Carica papaya L. is an important economic crop worldwide and is used as a model plant for sex-determination research. To study the different flower sex types, we screened sex-related genes using alternative splicing sequences (AS-seqs) from a transcriptome database of the three flower sex types, i.e., males, females, and hermaphrodites, established at 28 days before flowering using 15 bacterial artificial chromosomes (BACs) of C. papaya L. After screening, the cDNA regions of the three sex-related loci, including short vegetative phase-like (CpSVPL), the chromatin assembly factor 1 subunit A-like (CpCAF1AL), and the somatic embryogenesis receptor kinase (CpSERK), which contained eight sex-related single-nucleotide polymorphisms (SNPs) from the different sex types of C. papaya L., were genotyped using high-resolution melting (HRM). The three loci were examined regarding the profiles of the third whorl, as described below. CpSVPL, which had one SNP associated with the three sex genotypes, was highly expressed in the male and female sterile flowers (abnormal hermaphrodite flowers) that lacked the fourth whorl structure. CpCAF1AL, which had three SNPs associated with the male genotype, was highly expressed in male and normal hermaphrodite flowers, and had no AS-seqs, whereas it exhibited low expression and an AS-seqs in intron 11 in abnormal hermaphrodite flowers. Conversely, carpellate flowers (abnormal hermaphrodite flowers) showed low expression of CpSVPL and AS-seqs in introns 5, 6, and 7 of CpSERK, which contained four SNPs associated with the female genotype. Specifically, the CpSERK and CpCAF1AL loci exhibited no AS-seq expression in the third whorl of the male and normal hermaphrodite flowers, respectively, and variance in the AS-seq expression of all other types of flowers. Functional mapping of the third whorl of normal hermaphrodites indicated no AS-seq expression in CpSERK, low CpSVPL expression, and, for CpCAF1AL, high expression and no AS-seq expression on XY^h-type chromosomes.

Medicago truncatula SOC1 Genes Are Up-regulated by Environmental Cues That Promote Flowering

Like Arabidopsis thaliana, the flowering of the legume Medicago truncatula is promoted by long day (LD) photoperiod and vernalization. However, there are differences in the molecular mechanisms involved, with orthologs of two key Arabidopsis thaliana regulators, FLOWERING LOCUS C (FLC) and CONSTANS (CO), being absent or not having a role in flowering time function in Medicago. In Arabidopsis, the MADS-box transcription factor gene, SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (AtSOC1), plays a key role in integrating the photoperiodic and vernalization pathways. In this study, we set out to investigate whether the Medicago SOC1 genes play a role in regulating flowering time. Three Medicago SOC1 genes were identified and characterized (MtSOC1a-MtSOC1c). All three MtSOC1 genes, when heterologously expressed, were able to promote earlier flowering of the late-flowering Arabidopsis soc1-2 mutant. The three MtSOC1 genes have different patterns of expression. However, consistent with a potential role in flowering time regulation, all three MtSOC1 genes are expressed in the shoot apex and are up-regulated in the shoot apex of plants in response to LD photoperiods and vernalization. The up-regulation of MtSOC1 genes was reduced in Medicago fta1-1 mutants, indicating that they are downstream of MtFTa1. Insertion mutant alleles of Medicago soc1b do not flower late, suggestive of functional redundancy among Medicago SOC1 genes in promoting flowering.

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

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

Medicago truncatula: Genetic and Genomic Resources

Medicago truncatula was chosen by the legume community, along with Lotus japonicus, as a model plant to study legume biology. Since then, numerous resources and tools have been developed for M. truncatula. These include, for example, its genome sequence, core ecotype collections, transformation/regeneration methods, extensive mutant collections, and a gene expression atlas. This review aims to describe the different genetic and genomic tools and resources currently available for M. truncatula. We also describe how these resources were generated and provide all the information necessary to access these resources and use them from a practical point of view. © 2017 by John Wiley & Sons, Inc.

Characterization and Expression Analysis of PtAGL24, a SHORT VEGETATIVE PHASE/AGAMOUS-LIKE 24 (SVP/AGL24)-Type MADS-Box Gene from Trifoliate Orange (Poncirus trifoliata L. Raf.)

The transition from vegetative to reproductive growth in perennial woody plants does not occur until after several years of repeated seasonal changes and alternative growth. To better understand the molecular basis of flowering regulation in citrus, a MADS-box gene was isolated from trifoliate orange (precocious trifoliate orange, Poncirus trifoliata L. Raf.). Sequence alignment and phylogenetic analysis showed that the MADS-box gene is more closely related to the homologs of the AGAMOUS-LIKE 24 (AGL24) lineage than to any of the other MADS-box lineages known from Arabidopsis; it is named PtAGL24. Expression analysis indicated that PtAGL24 was widely expressed in the most organs of trifoliate orange, with the higher expression in mature flowers discovered by real-time PCR. Ectopic expression of PtAGL24 in wild-type Arabidopsis promoted early flowering and caused morphological changes in class I transgenic Arabidopsis. Yeast two-hybrid assay revealed that PtAGL24 interacted with Arabidopsis AtAGL24 and other partners of AtAGL24, suggesting that the abnormal morphology of PtAGL24 overexpression in transgenic Arabidopsis was likely due to the inappropriate interactions between exogenous and endogenous proteins. Also, PtAGL24 interacted with SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (PtSOC1) and APETALA1 (PtAP1) of citrus. These results suggest that PtAGL24 may play an important role in the process of floral transition but may have diverse functions in citrus development.

MtVRN2 is a Polycomb VRN2-like gene which represses the transition to flowering in the model legume Medicago truncatula

Optimising the timing of flowering contributes to successful sexual reproduction and yield in agricultural plants. FLOWERING LOCUS T (FT) genes, first identified in Arabidopsis thaliana (Arabidopsis), promote flowering universally, but the upstream flowering regulatory pathways can differ markedly among plants. Flowering in the model legume, Medicago truncatula (Medicago) is accelerated by winter cold (vernalisation) followed by long day (LD) photoperiods leading to elevated expression of the floral activator, FT-like gene FTa1. However, Medicago, like some other plants, lacks the activator CONSTANS (CO) and the repressor FLOWERING LOCUS C (FLC) genes which directly regulate FT and are key to LD and vernalisation responses in Arabidopsis. Conversely, Medicago has a VERNALISATION2-LIKE VEFS-box gene (MtVRN2). In Arabidopsis AtVRN2 is a key member of a Polycomb complex involved in stable repression of Arabidopsis FLC after vernalisation. VRN2-like genes have been identified in other eudicot plants, but their function has never been reported. We show that Mtvrn2 mutants bypass the need for vernalisation for early flowering in LD conditions in Medicago. Investigation of the underlying mechanism by transcriptome analysis reveals that Mtvrn2 mutants precociously express FTa1 and other suites of genes including floral homeotic genes. Double-mutant analysis indicates that early flowering is dependent on functional FTa1. The broad significance of our study is that we have demonstrated a function for a VRN2-like VEFS gene beyond the Brassicaceae. In particular, MtVRN2 represses the transition to flowering in Medicago by regulating the onset of expression of the potent floral activator, FTa1.

Functional characterization of GhSOC1 and GhMADS42 homologs from upland cotton (Gossypium hirsutum L.)

In Arabidopsis flowering pathway, MADS-box genes encode transcription factors, with their structures and functions highly conserved in many species. In our study, two MADS-box genes GhSOC1 and GhMADS42 (Gossypium hirsutum L.) were cloned from upland cotton CCRI36 and transformed into Arabidopsis. GhSOC1 was additionally transformed into upland cotton. Comparative analysis demonstrated sequence conservation between GhSOC1 and GhMADS42 and genes of other plant species. Tissue-specific expression analysis of GhSOC1 and GhMADS42 revealed spatiotemporal expression patterns involving high transcript levels in leaves, shoot apical buds, and flowers. In addition, overexpression of both GhSOC1 and GhMADS42 in Arabidopsis accelerated flowering, with GhMADS42 transgenic plants showing abnormal floral organ phenotypes. Overexpression of GhSOC1 in upland cotton also produced variations in floral organs. Furthermore, chromatin immunoprecipitation assay demonstrated that GhSOC1 could regulate GhMADS41 and GhMADS42, but not FLOWERING LOCUS T, by directly binding to the genes promoter. Finally, yeast two-hybrid and bimolecular fluorescence complementation approaches were undertaken to better understand the interaction of GhSOC1 and other MADS-box factors. These experiments showed that GhSOC1 can interact with APETALA1/FRUITFULL-like proteins in cotton.

Current status of tropical fruit breeding and genetics for three tropical fruit species cultivated in Japan: pineapple, mango, and papaya

Tropical fruit crops are predominantly produced in tropical and subtropical developing countries, but some are now grown in southern Japan. Pineapple (Ananas comosus), mango (Mangifera indica) and papaya (Carica papaya) are major tropical fruits cultivated in Japan. Modern, well-organized breeding systems have not yet been developed for most tropical fruit species. Most parts of Japan are in the temperate climate zone, but some southern areas such as the Ryukyu Islands, which stretch from Kyushu to Taiwan, are at the northern limits for tropical fruit production without artificial heating. In this review, we describe the current status of tropical fruit breeding, genetics, genomics, and biotechnology of three main tropical fruits (pineapple, mango, and papaya) that are cultivated and consumed in Japan. More than ten new elite cultivars of pineapple have been released with improved fruit quality and suitability for consumption as fresh fruit. New challenges and perspectives for obtaining high fruit quality are discussed in the context of breeding programs for pineapple.

Three Medicago MtFUL genes have distinct and overlapping expression patterns during vegetative and reproductive development and 35S:MtFULb accelerates flowering and causes a terminal flower phenotype in Arabidopsis

The timing of the transition to flowering is carefully controlled by plants in order to optimize sexual reproduction and the ensuing production of seeds, grains, and fruits. The genetic networks that regulate floral induction are best characterized in the temperate eudicot Arabidopsis in which the florigen gene FT plays a major role in promoting the transition to flowering. Legumes are an important plant group, but less is known about the regulation of their flowering time. In the model legume Medicago truncatula (Medicago), a temperate annual plant like Arabidopsis, flowering is induced by prolonged cold (vernalization) followed by long day lengths (LD). Recent molecular-genetic experiments have revealed that a FT-like gene, MtFTa1, is a central regulator of flowering time in Medicago. Here, we characterize the three Medicago FRUITFULL (FUL) MADS transcription factors, MtFULa, MtFULb, and MtFULc using phylogenetic analyses, gene expression profiling through developmental time courses, and functional analyses in transgenic plants. MtFULa and MtFULb have similarity in sequence and expression profiles under inductive environmental conditions during both vegetative and reproductive development while MtFULc is only up regulated in the apex after flowering in LD conditions. Sustained up regulation of MtFULs requires functional MtFTa1 but their transcript levels are not affected during cold treatment. Overexpression of MtFULa and MtFULb promotes flowering in transgenic Arabidopsis plants with an additional terminal flower phenotype on some 35S:MtFULb plants. An increase in transcript levels of the MtFULs was also observed in Medicago plants overexpressing MtFTa1. Our results suggest that the MtFULs are targets of MtFTa1. Overall, this work highlights the conserved functions of FUL-like genes in promoting flowering and other roles in plant development and thus contributes to our understanding of the genetic control of the flowering process in Medicago.

Genetic control of flowering time in legumes

The timing of flowering, and in particular the degree to which it is responsive to the environment, is a key factor in the adaptation of a given species to various eco-geographic locations and agricultural practices. Flowering time variation has been documented in many crop legumes, and selection for specific variants has permitted significant expansion and improvement in cultivation, from prehistoric times to the present day. Recent advances in legume genomics have accelerated the process of gene identification and functional analysis, and opened up new prospects for a molecular understanding of flowering time adaptation in this important crop group. Within the legumes, two species have been prominent in flowering time studies; the vernalization-responsive long-day species pea (Pisum sativum) and the warm-season short-day plant soybean (Glycine max). Analysis of flowering in these species is now being complemented by reverse genetics capabilities in the model legumes Medicago truncatula and Lotus japonicus, and the emergence of genome-scale resources in a range of other legumes. This review will outline the insights gained from detailed forward genetic analysis of flowering time in pea and soybean, highlighting the importance of light perception, the circadian clock and the FT family of flowering integrators. It discusses the current state of knowledge on genetic mechanisms for photoperiod and vernalization response, and concludes with a broader discussion of flowering time adaptation across legumes generally.

Overexpression of the kiwifruit SVP3 gene affects reproductive development and suppresses anthocyanin biosynthesis in petals, but has no effect on vegetative growth, dormancy, or flowering time

SVP-like MADS domain transcription factors have been shown to regulate flowering time and both inflorescence and flower development in annual plants, while having effects on growth cessation and terminal bud formation in perennial species. Previously, four SVP genes were described in woody perennial vine kiwifruit (Actinidia spp.), with possible distinct roles in bud dormancy and flowering. Kiwifruit SVP3 transcript was confined to vegetative tissues and acted as a repressor of flowering as it was able to rescue the Arabidopsis svp41 mutant. To characterize kiwifruit SVP3 further, ectopic expression in kiwifruit species was performed. Ectopic expression of SVP3 in A. deliciosa did not affect general plant growth or the duration of endodormancy. Ectopic expression of SVP3 in A. eriantha also resulted in plants with normal vegetative growth, bud break, and flowering time. However, significantly prolonged and abnormal flower, fruit, and seed development were observed, arising from SVP3 interactions with kiwifruit floral homeotic MADS-domain proteins. Petal pigmentation was reduced as a result of SVP3-mediated interference with transcription of the kiwifruit flower tissue-specific R2R3 MYB regulator, MYB110a, and the gene encoding the key anthocyanin biosynthetic step, F3GT1. Constitutive expression of SVP3 had a similar impact on reproductive development in transgenic tobacco. The flowering time was not affected in day-neutral and photoperiod-responsive Nicotiana tabacum cultivars, but anthesis and seed germination were significantly delayed. The accumulation of anthocyanin in petals was reduced and the same underlying mechanism of R2R3 MYB NtAN2 transcript reduction was demonstrated.

Unique and conserved features of floral evocation in legumes

Legumes, with their unique ability to fix atmospheric nitrogen, play a vital role in ensuring future food security and mitigating the effects of climate change because they use less fossil energy and produce less greenhouse gases compared with N-fertilized systems. Grain legumes are second only to cereal crops as a source of human and animal food, and they contribute approximately one third of the protein consumed by the human population. The productivity of seed crops, such as grain legumes, is dependent on flowering. Despite the genetic variation and importance of flowering in legume production, studies of the molecular pathways that control flowering in legumes are limited. Recent advances in genomics have revealed that legume flowering pathways are divergent from those of such model species as Arabidopsis thaliana. Here, we discuss the current understanding of flowering time regulation in legumes and highlight the unique and conserved features of floral evocation in legumes.