Molecular and genetic mechanisms of floral control

Tomato DC1 domain protein SlCHP16 interacts with the 14-3-3 protein TFT12 to regulate flower development

Flower development is of great significance for plant reproductive growth, but the molecular mechanisms underlying flower development remain to be fully understood. In this study, a tomato (Solanum lycopersicum L.) Divergent C1 (DC1) domain protein SlCHP16 was identified as a negative regulator of flower development. Overexpression of SlCHP16 led to the delay of flower bud development and failure of flowers to blossom and bear fruits. Conversely, down-regulation of SlCHP16 transcripts, via RNA interference (RNAi), led to formation of larger flowers in transgenic tomato plants. In SlCHP16-overexpressing plants, floral primordia and floral organs were initiated normally, but their subsequent growth and development were severely arrested. Transcriptome analysis showed that this arrest was associated with the changes in expression levels of a large number of genes involved in cell division and organ development. Tomato 14-3-3 protein 12 (TFT12) was identified as an interacting protein of SlCHP16 by tandem mass spectrometry, and its overexpression in tomato plants led to the formation of enlarged flowers. The presence of SlCHP16 disturbed the stability and homodimerization of TFT12 in plant cells. The results of this study demonstrate an inhibitory role of SlCHP16 in flower development in tomato by interaction with the 14-3-3 protein TFT12. This work provides new insights into the mechanisms that control development of floral organs.

Identification and breeding exploitation of dBrGMSP related to early bolting in Brassica rapa

Bolting is an important agronomic trait for stalk type of vegetable crops. Early bolting is a favorable characteristic for stalk type of Chinese cabbage variety, which has the advantage of early market supply. In the present study, we screened an EMS-mutagenized Chinese cabbage population and isolated a dominant gain-of-function early bolting mutant ebm16 which exhibited remarkable earlier bolting trait than its WT. BrGMSP, encoding a galactose mutarotase-like superfamily protein, was identified as the candidate gene via MutMap and KASP analysis. A C-T mutation existed in exon of BrGMSP in ebm16. Both transient overexpression in the WT and stable transgenic overexpression in Arabidopsis thaliana for the mutated gene dBrGMSP verified the function of BrGMSP in regulating early bolting. BrGMSP was localized in the nucleus. LCA proved that BrGMSP could interact with BrPGM1 controlling photosynthetic carbon flow. VIGS verified that BrPGM1 had the function on promoting bolting in Chinese cabbage. It was proved that dBrGMSP could be applied in breeding for stalk type of Chinese cabbage.

The PEBP genes FLOWERING LOCUS T and TERMINAL FLOWER 1 modulate seed dormancy and size

The phosphatidylethanolamine-binding protein (PEBP) family members FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) are major regulators of plant reproduction. In Arabidopsis, the FT/TFL1 balance defines the timing of floral transition and the determination of inflorescence meristem identity. However, emerging studies have elucidated a plethora of previously unknown functions for these genes in various physiological processes. Here, we characterized potential roles in seed size and dormancy of FT and TFL1 in Arabidopsis thaliana using CRISPR mutants and reporter analysis. Our findings unveiled a role for TFL1 in seed dormancy while confirming the role of FT in regulating this trait. We showed that the interplay between these two genes in seed dormancy is antagonistic, mirroring their roles in flowering time and inflorescence architecture. Analysis of reporter lines demonstrated that FT and TFL1 are partly co-expressed in seeds. Finally, we showed that total seed yield is affected in these mutants. Together, our results highlight the versatility of these two genes beyond their canonical functions. The impact of FT and TFL1 on seed characteristics emphasizes the significance of approaching gene studies from various perspectives, enabling the identification of multifaceted molecular factors that could play a major role in shaping the future of agriculture.

Genome-wide identification of the E-class gene family in wheat: evolution, expression, and interaction

Introduction

Wheat (Triticum aestivum L.) is among themost important crop worldwide. Given a growing population and changing climate, enhancing wheat yield is of great importance. Yield is closely associated with flower and spike development, and E-class genes play important roles in the flower and kernel development of plants. Currently, the absence of systematic analysis on the E gene family hinders our comprehension of their roles in plant growth and development.

Methods

Identify E-class genes based on homologous sequence searches. Analyze the identified E-class genes through a series of gene family analyses. Determine the expression levels of wheat E-class genes by searching public databases. Validate the functions of these genes by transforming them into Arabidopsis. Finally, determine the interactions between the genes through yeast two-hybrid experiments.

Results

Fifteen E-class genes (TaEs) were identified in common wheat. Nine E-class genes were detected in five ancestral/closely related species, including one in Aegilops tauschii (AtE), one in T. Urartu (TuEs), two in T. turgidum (TtEs), two in T. dicoccoides (TdEs), and three in T. spelta (TsEs). The 24 E-class genes were classified into three subgroups using a phylogenetic approach. All genes were highly expressed in spikes, and most were only highly expressed at the floret meristem stage. The effects of TaSEP5-A on flowering and growth cycles were confirmed in homologous mutants and transgenic Arabidopsis thaliana. The E-class genes were able to regulate the growth cycle of Arabidopsis. Finally, we confirmed the interactions between TaSEP5-A and other wheat E-class genes based on yeast two-hybrid assays.

Discussion

Our findings provide information regarding the E-class genes in wheat and will potentially promote the application of these genes in wheat improvement.

Analysis on morphological characteristics and identification of candidate genes during the flowering development of alfalfa

Flower development is a crucial and complex process in the reproductive stage of plants, which involves the interaction of multiple endogenous signals and environmental factors. However, regulatory mechanism of flower development was unknown in alfalfa (Medicago sativa). In this study, the three stages of flower development of 'M. sativa cv. Gannong No. 5' (G5) and its early flowering and multi flowering mutant (MG5) were comparatively analyzed by transcriptomics. The results showed that compared with late bud stage (S1), 14287 and 8351 differentially expressed genes (DEGs) were identified at early flower stage (S2) in G5 and MG5, and 19941 and 19469 DEGs were identified at late flower stage (S3). Compared with S2, 9574 and 10870 DEGs were identified at S3 in G5 and MG5, respectively. Venn analysis revealed that 547 DEGs were identified among the three comparison groups. KEGG pathway enrichment analysis showed that these genes were involved in the development of alfalfa flowers through redox pathways and plant hormone signaling pathways. Key candidate genes including SnRK2, BSK, GID1, DELLA and CRE1, for regulating the development from buds to mature flowers in alfalfa were screened. In addition, differential expression of transcription factors such as MYB, AP2, bHLH, C2C2, MADS-box, NAC, bZIP, B3 and AUX/IAA also played an important role in this process. The results laid a theoretical foundation for studying the molecular mechanisms of the development process from buds to mature flowers in alfalfa.

Ultrastructure and development of the floral nectary from Borago officinalis L. and phytochemical changes in its secretion

Although Boraginaceae have been classified as good sources of nectar for many insects, little is still known about their nectar and nectaries. Thus, in the present contribution, we investigated the nectar production dynamics and chemistry in Borago officinalis L. (borage or starflower), together with its potential interaction capacity with pollinators. A peak of nectar secretion (∼5.1 µL per flower) was recorded at anthesis, to decrease linearly during the following 9 days. In addition, TEM and SEM analyses were performed to understand ultrastructure and morphological changes occurring in borage nectary before and after anthesis, but also after its secretory phase. Evidence suggested that nectar was transported by the apoplastic route (mainly from parenchyma to epidermis) and then released essentially by exocytotic processes, that is a granulocrine secretion. This theory was corroborated by monitoring the signal of complex polysaccharides and calcium, respectively, via Thiéry staining and ESI/EELS technique. After the secretory phase, nectary underwent degeneration, probably through autophagic events and/or senescence induction. Furthermore, nectar (Nec) and other flower structures (i.e., sepals, gynoecia with nectaries, and petals) from borage were characterized by spectrophotometry and HPLC-DAD, in terms of plant secondary metabolites, both at early (E-) and late (L-) phase from anthesis. The content of phytochemicals was quantified and discussed for all samples, highlighting potential biological roles of these compounds in the borage flower (e.g., antimicrobial, antioxidant, staining effects). Surprisingly, a high significant accumulation of flavonoids was registered in L-Nec, with respect to E-Nec, indicating that this phenomenon might be functional and able to hide molecular (e.g., defence against pathogens) and/or ecological (e.g., last call for pollinators) purposes. Indeed, it is known that these plant metabolites influence nectar palatability, encouraging the approach of specialist pollinators, deterring nectar robbers, and altering the behaviour of insects.

HaMADS3, HaMADS7, and HaMADS8 are involved in petal prolongation and floret symmetry establishment in sunflower (Helianthus annuus L.)

The development of floral organs, crucial for the establishment of floral symmetry and morphology in higher plants, is regulated by MADS-box genes. In sunflower, the capitulum is comprised of ray and disc florets with various floral organs. In the sunflower long petal mutant (lpm), the abnormal disc (ray-like) floret possesses prolongated petals and degenerated stamens, resulting in a transformation from zygomorphic to actinomorphic symmetry. In this study, we investigated the effect of MADS-box genes on floral organs, particularly on petals, using WT and lpm plants as materials. Based on our RNA-seq data, 29 MADS-box candidate genes were identified, and their roles on floral organ development, especially in petals, were explored, by analyzing the expression levels in various tissues in WT and lpm plants through RNA-sequencing and qPCR. The results suggested that HaMADS3, HaMADS7, and HaMADS8 could regulate petal development in sunflower. High levels of HaMADS3 that relieved the inhibition of cell proliferation, together with low levels of HaMADS7 and HaMADS8, promoted petal prolongation and maintained the morphology of ray florets. In contrast, low levels of HaMADS3 and high levels of HaMADS7 and HaMADS8 repressed petal extension and maintained the morphology of disc florets. Their coordination may contribute to the differentiation of disc and ray florets in sunflower and maintain the balance between attracting pollinators and producing offspring. Meanwhile, Pearson correlation analysis between petal length and expression levels of MADS-box genes further indicated their involvement in petal prolongation. Additionally, the analysis of cis-acting elements indicated that these three MADS-box genes may regulate petal development and floral symmetry establishment by regulating the expression activity of HaCYC2c. Our findings can provide some new understanding of the molecular regulatory network of petal development and floral morphology formation, as well as the differentiation of disc and ray florets in sunflower.

Flowering onset time is regulated by microRNA-mediated trehalose-6-phosphate signaling in Cajanus cajan L. under elevated CO2

CO2 levels are known to have an impact on plant development and physiology. In the current study, we have investigated the effect of elevated CO2 on flowering and its regulation through miRNA mediated sugar signaling. We also unraveled small RNA transcriptome of pigeonpea under ambient and elevated CO2 conditions and predicted the targets for crucial miRNAs through computational methods. The results have shown that the delayed flowering in pigeonpea under elevated CO2 was due to an imbalance in C:N stoichiometry and differential expression pattern of aging pathway genes, including SQUAMOSA PROMOTER BINDING PROTEIN-LIKE. Furthermore, qRT PCR analysis has revealed the role of miR156 and miR172 in mediating trehalose-6-phosphate dependent flowering regulation. The current study is crucial in understanding the responses of flowering patterns in a legume crop to elevated CO2 which showed a significant impact on its final yields. Also, these findings are crucial in devising effective crop improvement strategies for developing climate resilient crops, including pigeonpea.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01434-9.

A novel single nucleotide mutation of TFL1 alters the plant architecture of Gossypium arboreum through changing the pre-mRNA splicing

KEY MESSAGE

A single nucleotide mutation from G to A at the 201st position changed the 5' splice site and deleted 31 amino acids in the first exon of GaTFL1. Growth habit is an important agronomic trait that plays a decisive role in the plant architecture and crop yield. Cotton (Gossypium) tends to indeterminate growth, which is unsuitable for the once-over mechanical harvest system. Here, we identified a determinate growth mutant (dt1) in Gossypium arboreum by EMS mutagenesis, in which the main axis was terminated with the shoot apical meristem (SAM) converted into flowers. The map-based cloning of the dt1 locus showed a single nucleotide mutation from G to A at the 201st positions in TERMINAL FLOWER 1 (GaTFL1), which changed the alternative RNA 5' splice site and resulted in 31 amino acids deletion and loss of function of GaTFL1. Comparative transcriptomic RNA-Seq analysis identified many transporters responsible for the phytohormones, auxin, sugar, and flavonoids, which may function downstream of GaTFL1 to involve the plant architecture regulation. These findings indicate a novel alternative splicing mechanism involved in the post-transcriptional modification and TFL1 may function upstream of the auxin and sugar pathways through mediating their transport to determine the SAM fate and coordinate the vegetative and reproductive development from the SAM of the plant, which provides clues for the TFL1 mechanism in plant development regulation and provide research strategies for plant architecture improvement.

Agronomic and hormonal approaches for enhancing flowering intensity in white Guinea yam (Dioscorea rotundata Poir.)

Developing novel white Guinea yam (Dioscorea rotundata) varieties is constrained by the sparse, erratic, and irregular flowering behavior of most genotypes. We tested the effectiveness of nine agronomic and hormonal treatments to enhance flowering on D. rotundata under field conditions. Genotypes responded differently to flower-inducing treatments (p<0.001). Of the test treatments, pruning and silver thiosulfate (STS) were effective in increasing the number of spikes per plant and the flowering intensity on both sparse flowering and monoecious cultivars. STS and tuber removal treatments promoted female flowers on the monoecious variety while pruning and most treatments involving pruning favored male flowers. None of the treatments induced flowering on Danacha, a non-flowering yam landrace. Flower-enhancing treatments had no significant effect on flower fertility translated by the fruit set, since most treatments recorded fruit sets above the species' average crossability rate. Flower-enhancing techniques significantly influenced number of tubers per plant (p = 0.024) and tuber dry matter content (DMC, p = 0.0018) but did not significantly affect plant tuber yield. Nevertheless, treatments that could enhance substantially flowering intensity, such as pruning and STS, reduced tuber yield. DMC had negative associations with all flowering-related traits. This study provided insights into white yam flower induction and suggests promising treatments that can be optimized and used routinely to increase flowering in yam crop, without significantly affecting flower fertility and tuber yield.

Fruit growth and development in apple: a molecular, genomics and epigenetics perspective

Fruit growth and development are physiological processes controlled by several internal and external factors. This complex regulatory mechanism comprises a series of events occurring in a chronological order over a growing season. Understanding the underlying mechanism of fruit development events, however, requires consideration of the events occurring prior to fruit development such as flowering, pollination, fertilization, and fruit set. Such events are interrelated and occur in a sequential order. Recent advances in high-throughput sequencing technology in conjunction with improved statistical and computational methods have empowered science to identify some of the major molecular components and mechanisms involved in the regulation of fruit growth and have supplied encouraging successes in associating genotypic differentiation with phenotypic observations. As a result, multiple approaches have been developed to dissect such complex regulatory machinery and understand the genetic basis controlling these processes. These methods include transcriptomic analysis, quantitative trait loci (QTLs) mapping, whole-genome approach, and epigenetics analyses. This review offers a comprehensive overview of the molecular, genomic and epigenetics perspective of apple fruit growth and development that defines the final fruit size and provides a detailed analysis of the mechanisms by which fruit growth and development are controlled. Though the main emphasis of this article is on the molecular, genomic and epigenetics aspects of fruit growth and development, we will also deliver a brief overview on events occurring prior to fruit growth.

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

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

Transcriptome Analysis Reveals the Regulatory Networks of Cytokinin in Promoting Floral Feminization in Castanea henryi

Castanea henryi is a monoecious plant with a low female-to-male ratio, which limits its yield. The phytohormone cytokinin (CK) plays a crucial role in flower development, especially gynoecium development. Here, the feminizing effect of CK on the development of C. henryi was confirmed by the exogenous spraying of N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU). Spraying CPPU at 125 mg·L^-1 thrice changed the male catkin into a pure female catkin, whereas at 5 mg·L^-1 and 25 mg·L^-1, only a part of the male catkin was transformed into a female catkin. A comparative transcriptome analysis of male catkins subjected to CPPU was performed to study the mechanism of the role of CKs in sex differentiation. Using Pearson's correlation analysis between hormone content and hormone synthesis gene expression, four key genes, LOG1, LOG3, LOG7 and KO, were identified in the CK and GA synthesis pathways. Moreover, a hub gene in the crosstalk between JA and the other hormone signaling pathways, MYC2, was identified, and 15 flowering-related genes were significantly differentially expressed after CPPU treatment. These results suggest that CK interacts with other phytohormones to determine the sex of C. henryi, and CK may directly target floral organ recognition genes to control flower sex.

Nitrate-dependent regulation of miR444-OsMADS27 signalling cascade controls root development in rice

Nitrate is an important nutrient and a key signalling molecule for plant development. A number of transcription factors involved in the response to nitrate and their regulatory mechanisms have been identified. However, little is known about the transcription factors involved in nitrate sensing and their regulatory mechanisms among crop plants. In this study, we identified functions of a nitrate-responsive miR444:MADS-box transcription factor OsMADS27 module and its downstream targets mediating rice root growth and stress responses. Transgenic rice plants expressing miR444 target mimic improved rice root growth. Although miR444 has the potential to target multiple genes, we identified OsMADS27 as the major miR444 target that regulates the expression of nitrate transporters, as well as several key genes including expansins, and those associated with auxin signalling, to promote root growth. In agreement with this, overexpression of miRNA-resistant OsMADS27 improved root development and tolerance to abiotic stresses, while its silencing suppressed root growth. OsMADS27 mediated robust stress tolerance in plants through its ability to bind to the promoters of specific stress regulators, as observed in ChIP-seq analysis. Our results provide evidence of a nitrate-dependent miR444-OsMADS27 signalling cascade involved in the regulation of rice root growth, as well as its surprising role in stress responses.

Genome-wide identification and characterization of mungbean CIRCADIAN CLOCK ASSOCIATED 1 like genes reveals an important role of VrCCA1L26 in flowering time regulation

Background

CIRCADIAN CLOCK ASSOCIATED 1 like (CCA1L) proteins are important components that participate in plant growth and development, and now have been characterized in multiple plant species. However, information on mungbean CCA1L genes is limited.

Results

In this study, we identified 27 VrCCA1L genes from the mungbean genome. VrCCA1L genes were unevenly distributed on 10 of the 11 chromosomes and showed one tandem and two interchromosomal duplication events. Two distinct kinds of conserved MYB domains, MYB 1 and MYB 2, were found, and the conserved SHAQK(Y/F) F sequence was found at the C terminus of each MYB 2 domain. The VrCCA1Ls displayed a variety of exon-intron organizations, and 24 distinct motifs were found among these genes. Based on phylogenetic analysis, VrCCA1L proteins were classified into five groups; group I contained the most members, with 11 VrCCA1Ls. VrCCA1L promoters contained different types and numbers of cis-acting elements, and VrCCA1Ls showed different expression levels in different tissues. The VrCCA1Ls also displayed distinct expression patterns under different photoperiod conditions throughout the day in leaves. VrCCA1L26 shared greatest homology to Arabidopsis CCA1 and LATE ELONGATED HYPOCOTYL (LHY). It delayed the flowering time in Arabidopsis by affecting the expression levels of CONSTANS (CO), FLOWERING LOCUS T (FT), and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1).

Conclusion

We identified and characterized 27 VrCCA1L genes from mungbean genome, and investigated their spatio-temporal expression patterns. Further analysis revealed that VrCCA1L26 delayed flowering time in transgenic Arabidopsis plants. Our results provide useful information for further functional characterization of the VrCCA1L genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08620-7.

Germplasm Resources and Strategy for Genetic Breeding of Lycium Species: A Review

Lycium species (goji), belonging to Solanaceae, are widely spread in the arid to semiarid environments of Eurasia, Africa, North and South America, among which most species have affinal drug and diet functions, resulting in their potential to be a superior healthy food. However, compared with other crop species, scientific research on breeding Lycium species lags behind. This review systematically introduces the present germplasm resources, cytological examination and molecular-assisted breeding progress in Lycium species. Introduction of the distribution of Lycium species around the world could facilitate germplasm collection for breeding. Karyotypes of different species could provide a feasibility analysis of fertility between species. The introduction of mapping technology has discussed strategies for quantitative trait locus (QTL) mapping in Lycium species according to different kinds of traits. Moreover, to extend the number of traits and standardize the protocols of trait detection, we also provide 1,145 potential traits (275 agronomic and 870 metabolic) in different organs based on different reference studies on Lycium, tomato and other Solanaceae species. Finally, perspectives on goji breeding research are discussed and concluded. This review will provide breeders with new insights into breeding Lycium species.

RNA-Binding Protein MAC5A Is Required for Gibberellin-Regulated Stamen Development

The development of floral organs is coordinated by an elaborate network of homeotic genes, and gibberellin (GA) signaling is involved in floral organ development; however, the underlying molecular mechanisms remain elusive. In the present study, we found that MOS4-ASSOCIATED COMPLEX 5A (MAC5A), which is a protein containing an RNA-binding motif, was involved in the development of sepals, petals, and stamens; either the loss or gain of MAC5A function resulted in stamen malformation and a reduced seed set. The exogenous application of GA considerably exacerbated the defects in mac5a null mutants, including fewer stamens and male sterility. MAC5A was predominantly expressed in pollen grains and stamens, and overexpression of MAC5A affected the expression of homeotic genes such as APETALA1 (AP1), AP2, and AGAMOUS (AG). MAC5A may interact with RABBIT EARS (RBE), a repressor of AG expression in Arabidopsis flowers. The petal defect in rbe null mutants was at least partly rescued in mac5a rbe double mutants. These findings suggest that MAC5A is a novel factor that is required for the normal development of stamens and depends on the GA signaling pathway.

Transcriptome Analysis of Flower Development and Mining of Genes Related to Flowering Time in Tomato (Solanum lycopersicum)

Flowering is a morphogenetic process in which angiosperms shift from vegetative growth to reproductive growth. Flowering time has a strong influence on fruit growth, which is closely related to productivity. Therefore, research on crop flowering time is particularly important. To better understand the flowering period of the tomato, we performed transcriptome sequencing of early flower buds and flowers during the extension period in the later-flowering “Moneymaker” material and the earlier-flowering “20965” homozygous inbred line, and we analyzed the obtained data. At least 43.92 million clean reads were obtained from 12 datasets, and the similarity with the tomato internal reference genome was 92.86–94.57%. Based on gene expression and background annotations, 49 candidate genes related to flowering time and flower development were initially screened, among which the greatest number belong to the photoperiod pathway. According to the expression pattern of candidate genes, the cause of early flowering of “20965” is predicted. The modes of action of the differentially expressed genes were classified, and the results show that they are closely related to hormone regulation and participated in a variety of life activities in crops. The candidate genes we screened and the analysis of their expression patterns provide a basis for future functional verification, helping to explore the molecular mechanism of tomato flowering time more comprehensively.

Stress-inducible Arabidopsis thaliana RD29A promoter constitutively drives Citrus sinensis APETALA1 and LEAFY expression and precocious flowering in transgenic Citrus spp

Transgenic 'Duncan' grapefruit (Citrus paradisi Macf.) and 'Valencia' sweet orange (Citrus sinensis [L.] Osbeck) plants ectopically expressing C. sinensis (cv. Washington navel orange) APETALA1 (CsAP1) or LEAFY (CsLFY) genes under control of the Arabidopsis thaliana stress-inducible promoter AtRD29A flowered under non-inductive (warm temperature, well-watered) greenhouse conditions, whereas their wild-type (WT) counterparts did not. The transgenic plants that flowered exhibited no altered morphological features, except the lack of thorns characteristic of juvenile WT plants. The most precocious T0 line, 'Duncan' grapefruit (Dun134-3) expressing the CsAP1 gene, flowered and fruited when it was 4.5 years old and the T1 siblings from this line flowered and fruited when they were just over 18 months old. In contrast, T1 seedlings from three lines of 'Duncan' grapefruit expressing the CsLFY gene flowered within 3 months after germination, but were unable to support fruit development. Transcript levels of corresponding transgenes in leaves were not correlated with earliness of flowering. To further study the activity of AtRD29A, leaves from three 'Carrizo' citrange (C. sinensis × Poncirus trifoliata) rootstock seedlings transformed with the green fluorescent protein (GFP) gene under regulation of the AtRD29A promoter were subjected to drought stress or well-watered conditions. Expression of GFP was not stress-dependent, consistent with the observation of flowering of CsAP1 and CsLFY transgenic plants under non-inductive conditions. Taken together, the results suggest that AtRD29A is constitutively expressed in a citrus background. Despite the loss of control over flowering time, transgenic citrus lines ectopically expressing C. sinensis AP1 or LFY genes under control of the A. thaliana RD29A promoter exhibit precocious flowering, fruit development and viable transgenic seed formation. These transformed lines can be useful tools to reduce the time between generations to accelerate breeding.

A MADS-Box Gene CiMADS43 Is Involved in Citrus Flowering and Leaf Development through Interaction with CiAGL9

MADS-box genes are involved in various developmental processes including vegetative development, flower architecture, flowering, pollen formation, seed and fruit development. However, the function of most MADS-box genes and their regulation mechanism are still unclear in woody plants compared with model plants. In this study, a MADS-box gene (CiMADS43) was identified in citrus. Phylogenetic and sequence analysis showed that CiMADS43 is a GOA-like Bsister MADS-box gene. It was localized in the nucleus and as a transcriptional activator. Overexpression of CiMADS43 promoted early flowering and leaves curling in transgenic Arabidopsis. Besides, overexpression or knockout of CiMADS43 also showed leaf curl phenotype in citrus similar to that of CiMADS43 overexpressed in Arabidopsis. Protein–protein interaction found that a SEPALLATA (SEP)-like protein (CiAGL9) interacted with CiMADS43 protein. Interestingly, CiAGL9 also can bind to the CiMADS43 promoter and promote its transcription. Expression analysis also showed that these two genes were closely related to seasonal flowering and the development of the leaf in citrus. Our findings revealed the multifunctional roles of CiMADS43 in the vegetative and reproductive development of citrus. These results will facilitate our understanding of the evolution and molecular mechanisms of MADS-box genes in citrus.

SiMADS34, an E-class MADS-box transcription factor, regulates inflorescence architecture and grain yield in Setaria italica

A novel MADS-box member SiMADS34 is essential for regulating inflorescence architecture and grain yield in Setaria italica. MADS-box transcription factors participate in regulating various developmental processes in plants. Inflorescence architecture is one of the most important agronomic traits and is closely associated with grain yield in most staple crops. Here, we isolated a panicle development mutant simads34 from a foxtail millet (Setaria italica (L.) P. Beauv.) EMS mutant library. The mutant showed significantly altered inflorescence architecture and decreased grain yield. Investigation of agronomic traits revealed increased panicle width by 16.8%, primary branch length by 10%, and number of primary branches by 30.9%, but reduced panicle length by 25.2%, and grain weight by 25.5% in simads34 compared with wild-type plants. Genetic analysis of a simads34 × SSR41 F₂ population indicated that the simads34 phenotype was controlled by a recessive gene. Map-based cloning and bulked-segregant analysis sequencing demonstrated that a single G-to-A transition in the fifth intron of SiMADS34 in the mutant led to an alternative splicing event and caused an early termination codon in this causal gene. SiMADS34 mRNA was expressed in all of the tissues tested, with high expression levels at the heading and panicle development stages. Subcellular localization analysis showed that simads34 predominantly accumulated in the nucleus. Transcriptome sequencing identified 241 differentially expressed genes related to inflorescence development, cell expansion, cell division, meristem growth and peroxide stress in simads34. Notably, an SPL14-MADS34-RCN pathway was validated through both RNA-seq and qPCR tests, indicating the putative molecular mechanisms regulating inflorescence development by SiMADS34. Our study identified a novel MADS-box member in foxtail millet and provided a useful genetic resource for inflorescence architecture and grain yield research.

Genes and genome editing tools for breeding desirable phenotypes in ornamentals

We review the main genes underlying commercial traits in cut flower species and critically discuss the possibility to apply genome editing approaches to produce novel variation and phenotypes. Promoting flowering and flower longevity as well as creating novelty in flower structure, colour range and fragrances are major objectives of ornamental plant breeding. The novel genome editing techniques add new possibilities to study gene function and breed new varieties. The implementation of such techniques, however, relies on detailed information about structure and function of genomes and genes. Moreover, improved protocols for efficient delivery of editing reagents are required. Recent results of the application of genome editing techniques to elite ornamental crops are discussed in this review. Enabling technologies and genomic resources are reviewed in relation to the implementation of such approaches. Availability of the main gene sequences, underlying commercial traits and in vitro transformation protocols are provided for the world's best-selling cut flowers, namely rose, lily, chrysanthemum, lisianthus, tulip, gerbera, freesia, alstroemeria, carnation and hydrangea. Results obtained so far are described and their implications for the improvement of flowering, flower architecture, colour, scent and shelf-life are discussed.

Spatio-Temporal Dynamics of the Patterning of Arabidopsis Flower Meristem

The qualitative model presented in this work recovers the onset of the four fields that correspond to those of each floral organ whorl of Arabidopsis flower, suggesting a mechanism for the generation of the positional information required for the differential expression of the A, B, and C identity genes according to the ABC model for organ determination during early stages of flower development. Our model integrates a previous model for the emergence of WUS pattern in the floral meristem, and shows that this pre-pattern is a necessary but not sufficient condition for the posterior information of the four fields predicted by the ABC model. Furthermore, our model predicts that LFY diffusion along the L1 layer of cells is not a necessary condition for the patterning of the floral meristem.

VrLELP controls flowering time under short-day conditions in Arabidopsis

Flowering time has a critically important effect on the reproduction of plants, and many components involved in flowering-time regulation have been identified in multiple plant species. However, studies of the flowering-time genes in mungbean (Vigna radiata) have been limited. Here, we characterized a novel mungbean gene, VrLELP, involved in flowering-time regulation in transgenic Arabidopsis. Subcellular localization analysis revealed that VrLELP was localized in the membrane, cytoplasm and nucleus and the nucleus and membrane contained higher signal than cytoplasm, similar to the empty vector control. The expression of VrLELP was higher in leaves and pods and lower in nodule roots relative to other tissues. The expression of VrLELP varied during flower development. The expression of VrLELP also varied during the day, reaching a peak after 12 h of illumination under long-day conditions. In contrast, under short-day conditions, the abundance of VrLELP transcripts changed little throughout the day. In addition, VrLELP delayed flowering time in transgenic Arabidopsis plants by suppressing the expression of the flowering-time genes CO and FT under short-day conditions. However, VrLELP did not affect flowering time under long-day conditions in Arabidopsis. Our study provides essential information for future studies of the molecular mechanisms of the flowering-time regulation system in mungbean.

Characterization of Mungbean CONSTANS-LIKE Genes and Functional Analysis of CONSTANS-LIKE 2 in the Regulation of Flowering Time in Arabidopsis

CONSTANS-LIKE (COL) genes play important roles in the regulation of plant growth and development, and they have been analyzed in many plant species. However, few studies have examined COL genes in mungbean (Vigna radiata). In this study, we identified and characterized 31 mungbean genes whose proteins contained B-Box domains. Fourteen were designated as VrCOL genes and were distributed on 7 of the 11 mungbean chromosomes. Based on their phylogenetic relationships, VrCOLs were clustered into three groups (I, II, and III), which contained 4, 6, and 4 members, respectively. The gene structures and conserved motifs of the VrCOL genes were analyzed, and two duplicated gene pairs, VrCOL1/VrCOL2 and VrCOL8/VrCOL9, were identified. A total of 82 cis-acting elements were found in the VrCOL promoter regions, and the numbers and types of cis-acting elements in each VrCOL promoter region differed. As a result, the expression patterns of VrCOLs varied in different tissues and throughout the day under long-day and short-day conditions. Among these VrCOL genes, VrCOL2 showed a close phylogenetic relationship with Arabidopsis thaliana CO and displayed daily oscillations in expression under short-day conditions but not long-day conditions. In addition, overexpression of VrCOL2 accelerated flowering in Arabidopsis under short-day conditions by affecting the expression of the flowering time genes AtFT and AtTSF. Our study lays the foundation for further investigation of VrCOL gene functions.

Characterization of C- and D-Class MADS-Box Genes in Orchids

Orchids (members of the Orchidaceae family) possess unique flower morphology and adaptive reproduction strategies. Although the mechanisms underlying their perianth development have been intensively studied, the molecular basis of reproductive organ development in orchids remains largely unknown. Here, we report the identification and functional characterization of two AGAMOUS (AG)-like MADS-box genes, Dendrobium 'Orchid' AG1 (DOAG1) and DOAG2, which are putative C- and D-class genes, respectively, from the orchid Dendrobium 'Chao Praya Smile'. Both DOAG1 and DOAG2 are highly expressed in the reproductive organ, known as the column, compared to perianth organs, while DOAG2 expression gradually increases in pace with pollination-induced ovule development and is localized in ovule primordia. Ectopic expression of DOAG1, but not DOAG2, rescues floral defects in the Arabidopsis (Arabidopsis thaliana) ag-4 mutant, including reiteration of stamenoid perianth organs in inner whorls and complete loss of carpels. Downregulation of DOAG1 and DOAG2 in orchids by artificial microRNA interference using l-Met sulfoximine selection-based gene transformation systems shows that both genes are essential for specifying reproductive organ identity, yet they, exert different roles in mediating floral meristem determinacy and ovule development, respectively, in Dendrobium spp. orchids. Notably, knockdown of DOAG1 and DOAG2 also affects perianth organ development in orchids. Our findings suggest that DOAG1 and DOAG2 not only act as evolutionarily conserved C- and D-class genes, respectively, in determining reproductive organ identity, but also play hitherto unknown roles in mediating perianth organ development in orchids.

Role of BrSDG8 on bolting in Chinese cabbage (Brassica rapa)

Mapping and resequencing of two allelic early bolting mutants ebm5-1 and ebm5-2 revealed that the BrSDG8 gene is related to bolting in Chinese cabbage (Brassica rapa ssp. pekinensis). Bolting influences the leafy head formation and seed yield of Chinese cabbage therefore being an important agronomic trait. Herein, two allelic early bolting mutants, ebm5-1 and ebm5-2, stably inherited in Chinese cabbage were obtained from wild-type 'FT' seeds by ethyl methane sulfonate mutagenesis. Both mutants flowered significantly earlier than 'FT,' and genetic analysis revealed that the early bolting of the two mutants was controlled by one recessive nuclear gene. With BSR-seq, the mutations originating lines ebm5-1 and ebm5-2 were located to the same region in chromosome A07. Using the 1741 F₂ individuals with the ebm5-1 phenotype as the mapping population, this region was narrowed to 56.24 kb between markers InDel18 and InDel45. A single-nucleotide polymorphism (SNP) was aligned to the BraA07g040740.3C (BrSDG8) region by whole-genome resequencing of ebm5-1 mutant and 'FT.' BrSDG8 is a homolog of Arabidopsis thaliana SDG8 encoding a histone methyltransferase affecting H3K4 trimethylation in FLOWERING LOCUS C chromatin. Comparative sequencing established that the SNP occurred on BrSDG8 17th exon in ebm5-1. Genotype analysis showed full co-segregation of the early bolting phenotype with this SNP. Cloning of allelic mutant ebm5-2 indicated that it harbors a deletion mutation on the 12th exon of BrSDG8. Quantitative real-time PCR analysis indicated that BrSDG8 expression level was observably lower in mutant ebm5-1 than in 'FT.' Overall, the present results provide strong evidence that BrSDG8 mutation leads to early bolting in Chinese cabbage, thereby providing a basis to understand the molecular mechanisms underlying this phenotype.

Alternative splicing of flowering time gene FT is associated with halving of time to flowering in coconut

Coconut palm has two distinct types-"tall" and "dwarf"-which differ morphologically. Tall coconut varieties need 8-10 years to start flowering, while dwarf coconut varieties only require 3-5 years. We compared seedling and reproductive stage transcriptomes for both coconut types to determine potential molecular mechanisms underlying control of flowering time in coconut. Several key genes in the photoperiod pathway were differentially expressed between seedling and reproductive leaf samples in both tall and dwarf coconut. These genes included suppressor of overexpression of constans (SOC1), flowering locus T (FT), and Apetala 1 (AP1). Alternative splicing analysis of genes in the photoperiod pathway further revealed that the FT gene produces different transcripts in tall compared to dwarf coconut. The shorter alternative splice variant of FT [which included a 6 bp deletion, alternative 3' splicing sites (A3SS)] was found to be exclusively present in dwarf coconut varieties but absent in most tall coconut varieties. Our results provide a valuable information resource as well as suggesting a probable mechanism for differentiation of flowering time onset in coconut, providing a target for future breeding work in accelerating time to flowering in this crop species.

Molecular genetic analyses of abiotic stress responses during plant reproductive development

Plant responses to abiotic stresses during vegetative growth have been extensively studied for many years. Daily environmental fluctuations can have dramatic effects on plant vegetative growth at multiple levels, resulting in molecular, cellular, physiological, and morphological changes. Plants are even more sensitive to environmental changes during reproductive stages. However, much less is known about how plants respond to abiotic stresses during reproduction. Fortunately, recent advances in this field have begun to provide clues about these important processes, which promise further understanding and a potential contribution to maximize crop yield under adverse environments. Here we summarize information from several plants, focusing on the possible mechanisms that plants use to cope with different types of abiotic stresses during reproductive development, and present a tentative molecular portrait of plant acclimation during reproductive stages. Additionally, we discuss strategies that plants use to balance between survival and productivity, with some comparison among different plants that have adapted to distinct environments.

Flowering in Persian walnut: patterns of gene expression during flower development

BACKGROUND

Flower development and sufficient fruit set are important parameters with respect to walnut yield. Knowledge about flowering genes of fruit trees can help to conduct better molecular breeding programs. Therefore, this study was carried out to investigate the expression pattern of some flowering genes (FT, SOC1, CAL, LFY and TFL1) in Persian walnut (cv. Chandler) during the growing season and winter dormancy.

RESULTS

The results showed that walnut flower induction and initiation in Shahmirzad, Iran occurred in early June and late September, respectively. After meeting chilling and heat requirement, flower differentiation and anthesis occurred in late-March and mid-April to early-May, respectively. Study of flowering gene expression showed that the expression of the FT gene increased in three stages including before breaking of bud dormancy, from late March to late April (coincided with flower differentiation and anthesis) and from late May to mid-June (coincided with flower induction). Like FT, the expression of SOC1 gene increased during flower induction and initiation (mid-May to early-August) as well as flower anthesis (mid-April to early-May). LFY and CAL genes as floral meristem identity genes are activated by FT and SOC1 genes. In contrast with flowering stimulus genes, TFL1 showed overexpression during winter dormancy which prevented flowering.

CONCLUSION

The expression of FT gene activated downstream floral meristem identity genes including SOC1, CAL and LFY which consequently led to release bud dormancy as well as flower anthesis and induction. Also, TFL1 as a flowering inhibitor gene in walnut showed overexpression during the bud dormancy. Chilling accumulation reduced TFL1 gene expression and increased the expression of flowering genes which ultimately led to overcome dormancy.

Mechanism of Allium Crops Bulb Enlargement in Response to Photoperiod: A Review

The photoperiod marks a varied set of behaviors in plants, including bulbing. Bulbing is controlled by inner signals, which can be stimulated or subdued by the ecological environment. It had been broadly stated that phytohormones control the plant development, and they are considered to play a significant part in the bulb formation. The past decade has witnessed significant progress in understanding and advancement about the photoperiodic initiation of bulbing in plants. A noticeable query is to what degree the mechanisms discovered in bulb crops are also shared by other species and what other qualities are also dependent on photoperiod. The FLOWERING LOCUS T (FT) protein has a role in flowering; however, the FT genes were afterward reported to play further functions in other biological developments (e.g., bulbing). This is predominantly applicable in photoperiodic regulation, where the FT genes seem to have experienced significant development at the practical level and play a novel part in the switch of bulb formation in Alliums. The neofunctionalization of FT homologs in the photoperiodic environments detects these proteins as a new class of primary signaling mechanisms that control the growth and organogenesis in these agronomic-related species. In the present review, we report the underlying mechanisms regulating the photoperiodic-mediated bulb enlargement in Allium species. Therefore, the present review aims to systematically review the published literature on the bulbing mechanism of Allium crops in response to photoperiod. We also provide evidence showing that the bulbing transitions are controlled by phytohormones signaling and FT-like paralogues that respond to independent environmental cues (photoperiod), and we also show that an autorelay mechanism involving FT modulates the expression of the bulbing-control gene. Although a large number of studies have been conducted, several limitations and research gaps have been identified that need to be addressed in future studies.

MicroRNAs and their targeted genes associated with phase changes of stem explants during tissue culture of tea plant

Elucidation of the molecular mechanism related to the dedifferentiation and redifferentiation during tissue culture will be useful for optimizing regeneration system of tea plant. In this study, an integrated sRNAome and transcriptome analyses were carried out during phase changes of the stem explant culture. Among 198 miRNAs and 8001 predicted target genes, 178 differentially expressed miRNAs and 4264 potential targets were screened out from explants, primary calli, as well as regenerated roots and shoots. According to KEGG analysis of the potential targets, pathway of "aminoacyl-tRNA biosynthesis", "proteasome" and "glutathione metabolism" was of great significance during the dedifferentiation, and pathway of "porphyrin and chlorophyll metabolism", "mRNA surveillance pathway", "nucleotide excision repair" was indispensable for redifferentiation of the calli. Expression pattern of 12 miRNAs, including csn-micR390e, csn-miR156b-5p, csn-miR157d-5p, csn-miR156, csn-miR166a-3p, csn-miR166e, csn-miR167d, csn-miR393c-3p, csn-miR394, csn-miR396a-3p, csn-miR396 and csn-miR396e-3p, was validated by qRT-PCR among 57 differentially expressed phase-specific miRNAs. Validation also confirmed that regulatory module of csn-miR167d/ERF3, csn-miR156/SPB1, csn-miR166a-3p/ATHB15, csn-miR396/AIP15A, csn-miR157d-5p/GST and csn-miR393c-3p/ATG18b might play important roles in regulating the phase changes during tissue culture of stem explants.

The Terrestrial Carnivorous Plant Utricularia reniformis Sheds Light on Environmental and Life-Form Genome Plasticity

Utricularia belongs to Lentibulariaceae, a widespread family of carnivorous plants that possess ultra-small and highly dynamic nuclear genomes. It has been shown that the Lentibulariaceae genomes have been shaped by transposable elements expansion and loss, and multiple rounds of whole-genome duplications (WGD), making the family a platform for evolutionary and comparative genomics studies. To explore the evolution of Utricularia, we estimated the chromosome number and genome size, as well as sequenced the terrestrial bladderwort Utricularia reniformis (2n = 40, 1C = 317.1-Mpb). Here, we report a high quality 304 Mb draft genome, with a scaffold NG50 of 466-Kb, a BUSCO completeness of 87.8%, and 42,582 predicted genes. Compared to the smaller and aquatic U. gibba genome (101 Mb) that has a 32% repetitive sequence, the U. reniformis genome is highly repetitive (56%). The structural differences between the two genomes are the result of distinct fractionation and rearrangements after WGD, and massive proliferation of LTR-retrotransposons. Moreover, GO enrichment analyses suggest an ongoing gene birth-death-innovation process occurring among the tandem duplicated genes, shaping the evolution of carnivory-associated functions. We also identified unique patterns of developmentally related genes that support the terrestrial life-form and body plan of U. reniformis. Collectively, our results provided additional insights into the evolution of the plastic and specialized Lentibulariaceae genomes.

Comprehensive characterization of a floral mutant reveals the mechanism of hooked petal morphogenesis in Chrysanthemum morifolium

The diversity of form of the chrysanthemum flower makes this species an ideal model for studying petal morphogenesis, but as yet, the molecular mechanisms underlying petal shape development remain largely unexplored. Here, a floral mutant, which arose as a bud sport in a plant of the variety 'Anastasia Dark Green', and formed straight, rather than hooked petals, was subjected to both comparative morphological analysis and transcriptome profiling. The hooked petals only became discernible during a late stage of flower development. At the late stage of 'Anastasia Dark Green', genes related to chloroplast, hormone metabolism, cell wall and microtubules were active, as were cell division-promoting factors. Auxin concentration was significantly reduced, and a positive regulator of cell expansion was down-regulated. Two types of critical candidates, boundary genes and adaxial-abaxial regulators, were identified from 7937 differentially expressed genes in pairwise comparisons, which were up-regulated at the late stage in 'Anastasia Dark Green' and another two hooked varieties. Ectopic expression of a candidate abaxial gene, CmYAB1, in chrysanthemum led to changes in petal curvature and inflorescence morphology. Our findings provide new insights into the regulatory networks underlying chrysanthemum petal morphogenesis.

Molecular and transcriptional characterization of phosphatidyl ethanolamine-binding proteins in wild peanuts Arachis duranensis and Arachis ipaensis

BACKGROUND

Phosphatidyl ethanolamine-binding proteins (PEBPs) are involved in the regulation of plant architecture and flowering time. The functions of PEBP genes have been studied in many plant species. However, little is known about the characteristics and expression profiles of PEBP genes in wild peanut species, Arachis duranensis and Arachis ipaensis, the diploid ancestors of cultivated peanuts.

RESULTS

In this study, genome-wide identification methods were used to identify and characterize a total of 32 peanut PEBP genes, 16 from each of the two wild peanut species, A. duranensis and A. ipaensis. These PEBP genes were classified into 3 groups (TERMINAL FLOWER1-like, FLOWERING LOCUS T-like, and MOTHER OF FT AND TFL1-like) based on their phylogenetic relationships. The gene structures, motifs, and chromosomal locations for each of these PEBPs were analyzed. In addition, 4 interchromosomal duplications and 1 tandem duplication were identified in A. duranensis, and 2 interchromosomal paralogs and 1 tandem paralog were identified in A. ipaensis. Ninety-five different cis-acting elements were identified in the PEBP gene promoter regions and most genes had different numbers and types of cis-elements. As a result, the transcription patterns of these PEBP genes varied in different tissues and under long day and short day conditions during different growth phases, indicating the functional diversities of PEBPs in different tissues and their potential functions in plant photoperiod dependent developmental pathways. Moreover, our analysis revealed that AraduF950M/AraduWY2NX in A. duranensis, and Araip344D4/Araip4V81G in A. ipaensis are good candidates for regulating plant architecture, and that Aradu80YRY, AraduYY72S, and AraduEHZ9Y in A. duranensis and AraipVEP8T in A. ipaensis may be key factors regulating flowering time.

CONCLUSION

Sixteen PEBP genes were identified and characterized from each of the two diploid wild peanut genomes, A. duranensis and A. ipaensis. Genetic characterization and spatio-temporal expression analysis support their importance in plant growth and development. These findings further our understanding of PEBP gene functions in plant species.

Strigolactone represses the synthesis of melatonin, thereby inducing floral transition in Arabidopsis thaliana in an FLC-dependent manner

The transition from vegetative to reproductive growth is a key developmental event in a plant's life cycle. The process is mediated by a combination of phytohormones, including melatonin (MT) and strigolactone (SL). Here, the Arabidopsis mutants, d14-1 and max4-1, which are compromised with respect to either SL synthesis or signaling, were shown to flower earlier than wild types. The tissue MT content in both mutants was higher than in wild types, as a result of the up-regulation of various genes encoding enzymes involved in MT synthesis. The abundance in the mutants of transcripts derived from each of the genes SPLs, AP1, and SOC1 was reduced with exogenously supplied MT, while FLC was induced. Plants exposed to a high concentration of MT did not flower earlier than wild types. The tissue MT content of a mutant unable to synthesize caffeic acid O-methyltransferase was less than that of wild type and flowered earlier than did wild types. The suggestion is that the flowering time of Arabidopsis is altered if the tissue content of MT is either higher than ~ 8 ng/g F.W, or lower than ~ 0.9 ng/g. Within this range, SL acts to determine flowering time by its regulation of SPL genes. The application of exogenous SL reduces tissue MT content. The flowering time of the flc-3 mutant was unaffected by exogenously supplying either MT or/and SL. It is proposed that MT acts downstream of SL to activate FLC, inducing a delay to flowering if its concentration lies outside a certain range.

CsTFL1 inhibits determinate growth and terminal flower formation through interaction with CsNOT2a in cucumber

Cucumber (Cucumis sativus L.) is an important vegetable crop that carries on vegetative growth and reproductive growth simultaneously. Indeterminate growth is favourable for fresh market under protected environments, whereas determinate growth is preferred for pickling cucumber in the once-over mechanical harvest system. The genetic basis of determinacy is largely unknown in cucumber. In this study, map-based cloning of the de locus showed that the determinate growth habit is caused by a non-synonymous SNP in CsTFL1CsTFL1 is expressed in the subapical regions of the shoot apical meristem, lateral meristem and young stems. Ectopic expression of CsTFL1 rescued the terminal flower phenotype in the Arabidopsis tfl1-11 mutant and delayed flowering in wild-type Arabidopsis Knockdown of CsTFL1 resulted in determinate growth and formation of terminal flowers in cucumber. Biochemical analyses indicated that CsTFL1 interacts with a homolog of the miRNA biogenesis gene CsNOT2a; CsNOT2a interacts with FDP. Cucumber CsFT directly interacts with CsNOT2a and CsFD, and CsFD interacts with two 14-3-3 proteins. These data suggest that CsTFL1 competes with CsFT for interaction with CsNOT2a-CsFDP to inhibit determinate growth and terminal flower formation in cucumber.

Expression Analysis and Regulation Network Identification of the CONSTANS-Like Gene Family in Moso Bamboo (Phyllostachys edulis) Under Photoperiod Treatments

CONSTANS (CO)/CONSTANS-like (COL) genes that have been studied in annual model plants such as Arabidopsis thaliana and Oryza sativa play key roles in the photoperiodic flowering pathway. Moso bamboo is a perennial plant characterized by a long vegetative stage and flowers synchronously followed by widespread death. However, the characteristics of COL in moso bamboo remain unclear. In view of this, we performed a genome-wide identification and expression analysis of the COL gene family in moso bamboo. Fourteen nonredundant PheCOL genes were identified, and we analyzed gene structures, phylogeny, and subcellular location predictions. Phylogenetic analyses indicated that 14 PheCOLs could be clustered into three groups, and each clade was well supported by conserved intron/exon structures and motifs. A number of light-related and tissue-specific cis-elements were randomly distributed within the promoter sequences of the PheCOLs. The expression profiling of PheCOL genes in various tissues and developmental stages revealed that most of PheCOL genes were most highly expressed in the leaves and took part in moso bamboo flower development and rapid shoot growth. In addition, the transcription of PheCOLs exhibited a clear diurnal oscillation in both long-day and short-day conditions. Most of the PheCOL genes were inhibited under light treatment and upregulated in dark conditions. PheCOLs can interact with each other. Subcellular localization result showed that PheCOL14 encoded a cell membrane protein, and it bound to the promoter of PheCOL3. Taken together, the results of this study will be useful not only as they contribute to comprehensive information for further analyses of the molecular functions of the PheCOL gene family, but also will provide a theoretical foundation for the further construction of moso bamboo photoperiod regulation networks.

Rice Flower Development Revisited: Regulation of Carpel Specification and Flower Meristem Determinacy

The ABC model in flower development represents a milestone of plant developmental studies and is essentially conserved across a wide range of angiosperm species. Despite this overall conservation, individual genes in the ABC model are not necessarily conserved and sometimes play a species-specific role, depending on the plant. We previously reported that carpels are specified by the YABBY gene DROOPING LEAF (DL) in rice (Oryza sativa), which bears flowers that are distinct from those of eudicots. In contrast, another group reported that carpels are specified by two class C genes, OsMADS3 and OsMADS58. Here, we have addressed this controversial issue by phenotypic characterization of floral homeotic gene mutants. Analysis of a complete loss-of-function mutant of OsMADS3 and OsMADS58 revealed that carpel-like organs expressing DL were formed in the absence of the two class C genes. Furthermore, no known flower organs including carpels were specified in a double mutant of DL and SUPERWOMAN1 (a class B gene), which expresses only class C genes in whorls 3 and 4. These results suggest that, in contrast to Arabidopsis, class C genes are not a key regulator for carpel specification in rice. Instead, they seem to be involved in the elaboration of carpel morphology rather than its specification. Our phenotypic analysis also revealed that, similar to its Arabidopsis ortholog CRABS CLAW, DL plays an important function in regulating flower meristem determinacy in addition to carpel specification.

Reduced Expression of CbUFO Is Associated with the Phenotype of a Flower-Defective Cosmos bipinnatus

LEAFY (LFY) and UNUSUAL FLORAL ORGANS (UFO) homologous genes have been reported to play key roles in promoting the initiation of floral meristems in raceme- and cyme-type plants. Asteraceae, a large family of plants with more than 23,000 species, has a unique head-like inflorescence termed capitulum. Here, we report a floral defective plant of the garden cosmos named green head (gh), which shows homogeneous inflorescence, indistinguishable inflorescence periphery and center, and the replacement of flower meristems by indeterminate inflorescence meristems, coupled with iterative production of bract-like organs and higher order of inflorescences. A comparison of the LFY- and UFO-like genes (CbFLY and CbUFO) isolated from both the wild-type and gh cosmos revealed that CbUFO may play an important role in inflorescence differentiation into different structures and promotion of flower initiation, and the reduced expression of CbUFO in the gh cosmos could be associated with the phenotypes of the flower-defective plants. Further expression analysis indicated that CbUFO may promote the conversion of inflorescence meristem into floral meristem in early ray flower formation, but does not play a role in its later growth period.

Long Non-Coding RNAs: Rising Regulators of Plant Reproductive Development

Long non-coding RNAs (lncRNAs) exert a multitude of functions in regulating numerous biological processes. Recent studies have uncovered a growing number of lncRNAs within the plant genome. These molecules show striking tissue-specific expression patterns, suggesting that they exert regulatory functions in the growth and development processes of plants. Plant reproductive development is tightly regulated by both environmental and endogenous factors. As plant reproductive development is a crucial aspect of crop breeding, lncRNAs that modulate reproductive development are now particularly worth regarding. Here, we summarize findings that implicate lncRNAs in the control of plant reproductive development, especially in flowering control. Additionally, we elaborate on the regulation mechanisms of lncRNAs, tools for research on their function and mechanism, and potential directions of future research.

Genome-Wide Identification of Flowering-Time Genes in Brassica Species and Reveals a Correlation between Selective Pressure and Expression Patterns of Vernalization-Pathway Genes in Brassica napus

Flowering time is a key agronomic trait, directly influencing crop yield and quality. Many flowering-time genes have been identified and characterized in the model plant Arabidopsis thaliana; however, these genes remain uncharacterized in many agronomically important Brassica crops. In this study, we identified 1064, 510, and 524 putative orthologs of A. thaliana flowering-time genes from Brassica napus, Brassica rapa, and Brassica oleracea, respectively, and found that genes involved in the aging and ambient temperature pathways were fewer than those in other flowering pathways. Flowering-time genes were distributed mostly on chromosome C03 in B. napus and B. oleracea, and on chromosome A09 in B. rapa. Calculation of non-synonymous (Ka)/synonymous substitution (Ks) ratios suggested that flowering-time genes in vernalization pathways experienced higher selection pressure than those in other pathways. Expression analysis showed that most vernalization-pathway genes were expressed in flowering organs. Approximately 40% of these genes were highly expressed in the anther, whereas flowering-time integrator genes were expressed in a highly organ-specific manner. Evolutionary selection pressures were negatively correlated with the breadth and expression levels of vernalization-pathway genes. These findings provide an integrated framework of flowering-time genes in these three Brassica crops and provide a foundation for deciphering the relationship between gene expression patterns and their evolutionary selection pressures in Brassica napus.

Nitrogen use efficiency is regulated by interacting proteins relevant to development in wheat

Wheat (Triticum aestivum) has low nitrogen use efficiency (NUE). The genetic mechanisms controlling NUE are unknown. Positional cloning of a major quantitative trait locus for N-related agronomic traits showed that the vernalization gene TaVRN-A1 was tightly linked with TaNUE1, the gene shown to influence NUE in wheat. Because of an Ala180 /Val180 substitution, TaVRN-A1a and TaVRN-A1b proteins interact differentially with TaANR1, a protein encoded by a wheat orthologue of Arabidopsis nitrate regulated 1 (ANR1). The transcripts of both TaVRN-A1 and TaANR1 were down-regulated by nitrogen. TaANR1 was functionally characterized in TaANR1::RNAi transgenic wheat, and in a natural mutant with a 23-bp deletion including 10-bp at the 5' end of intron 5 and 13-bp of exon 6 in gDNA sequence in its gDNA sequence, which produced transcript that lacked the full 84-bp exon 6. Both TaANR1 and TaHOX1 bound to the Ala180 /Val180 position of TaVRN-A1. Genetically incorporating favourable alleles from TaVRN-A1, TaANR1 and TaHOX1 increased grain yield from 9.84% to 11.58% in the field. Molecular markers for allelic variation of the genes that regulate nitrogen can be used in breeding programmes aimed at improving NUE and yield in novel wheat cultivars.

Genome-Based Prediction of Time to Curd Induction in Cauliflower

The development of cauliflower (Brassica oleracea var. botrytis) is highly dependent on temperature due to vernalization requirements, which often causes delay and unevenness in maturity during months with warm temperatures. Integrating quantitative genetic analyses with phenology modeling was suggested to accelerate breeding strategies toward wide-adaptation cauliflower. The present study aims at establishing a genome-based model simulating the development of doubled haploid (DH) cauliflower lines to predict time to curd induction of DH lines not used for model parameterization and test hybrids derived from the bi-parental cross. Leaf appearance rate and the relation between temperature and thermal time to curd induction were examined in greenhouse trials on 180 DH lines at seven temperatures. Quantitative trait loci (QTL) analyses carried out on model parameters revealed ten QTL for leaf appearance rate (LAR), five for the slope and two for the intercept of linear temperature-response functions. Results of the QTL-based phenology model were compared to a genomic selection (GS) model. Model validation was carried out on data comprising four field trials with 72 independent DH lines, 160 hybrids derived from the parameterization set, and 34 hybrids derived from independent lines of the population. The QTL model resulted in a moderately accurate prediction of time to curd induction (R2 = 0.42-0.51) while the GS model generated slightly better results (R2 = 0.52-0.61). Predictions of time to curd induction of test hybrids from independent DH lines were less precise with R2 = 0.40 for the QTL and R2 = 0.48 for the GS model. Implementation of juvenile-to-adult phase transition is proposed for model improvement.

An APETALA2 Homolog, RcAP2, Regulates the Number of Rose Petals Derived From Stamens and Response to Temperature Fluctuations

Rosa chinensis, which is a famous traditional flower in China, is a major ornamental plant worldwide. Long-term cultivation and breeding have resulted in considerable changes in the number of rose petals, while most wild Rosaceae plants have only one whorl consisting of five petals. The petals of double flowers reportedly originate from stamens, but the underlying molecular mechanism has not been fully characterized. In this study, we observed that the number of petals of R. chinensis 'Old Blush' flowers increased and decreased in response to low- and high-temperature treatments, respectively, similar to previous reports. We characterized these variations in further detail and found that the number of stamens exhibited the opposite trend. We cloned an APETALA2 homolog, RcAP2. A detailed analysis of gene structure and promoter cis-acting elements as well as RcAP2 temporospatial expression patterns and responses to temperature changes suggested that RcAP2 expression may be related to the number of petals from stamen origin. The overexpression of RcAP2 in Arabidopsis thaliana transgenic plants may induce the transformation of stamens to petals, thereby increasing the number of petals. Moreover, silencing RcAP2 in 'Old Blush' plants decreased the number of petals. Our results may be useful for clarifying the temperature-responsive mechanism involved in petaloid stamen production, which may be relevant for the breeding of new rose varieties with enhanced flower traits.

MADS-domain transcription factors and the floral quartet model of flower development: linking plant development and evolution

The floral quartet model of floral organ specification poses that different tetramers of MIKC-type MADS-domain transcription factors control gene expression and hence the identity of floral organs during development. Here, we provide a brief history of the floral quartet model and review several lines of recent evidence that support the model. We also describe how the model has been used in contemporary developmental and evolutionary biology to shed light on enigmatic topics such as the origin of land and flowering plants. Finally, we suggest a novel hypothesis describing how floral quartet-like complexes may interact with chromatin during target gene activation and repression.

Isolation and functional characterization of a circadian-regulated CONSTANS homolog (GbCO) from Ginkgo biloba

This is the first report to clone and functionally characterize a flowering time gene GbCO in perennial gymnosperm Ginkgo biloba. GbCO complements the co mutant of Arabidopsis, restoring normal early flowering. CONSTANS (CO) is a central regulator of photoperiod pathway, which channels inputs from light, day length, and circadian clock to promote the floral transition. In order to understand the role of CO in gymnosperm Ginkgo biloba, which has a long juvenile phase (15-20 years), a CO homolog (GbCO) was isolated and characterized from G. biloba. GbCO encodes a 1741-bp gene with a predicted protein of 400 amino acids with two zinc finger domains (B-box I and B-box II) and a CCT domain. Phylogenic analysis classified GbCO into the group 1a clade of CO families in accordance with the grouping scheme for Arabidopsis CO (AtCO). Southern blot analysis indicated that GbCO belongs to a multigene family in G. biloba. Real-time PCR analysis showed that GbCO was expressed in aerial parts of Ginkgo, with the highest transcript level of GbCO being observed in shoot apexes. GbCO transcript level exhibited a strong diurnal rhythm under flowering-inductive long days and peaked during early morning, suggesting that GbCO is tightly coupled to the floral inductive long-day signal. In addition, an increasing trend of GbCO transcript level was observed both in shoot tips and leaves as the shoot growth under long-day condition, whereas GbCO transcript level decreased in both tissues under short-day condition prior to growth cessation of shoot in G. biloba. GbCO complemented the Arabidopsis co-2 mutant, restoring normal early flowering. All the evidence being taken together, our findings suggested that GbCO served as a potential inducer of flowering in G. biloba.

Tissue-specific transcriptomic profiling provides new insights into the reproductive ecology and biology of the iconic seagrass species Posidonia oceanica

Seagrasses form extensive meadows in shallow coastal waters and are among the world's most productive ecosystems. Seagrasses can produce both clonally and sexually, and flowering has long been considered infrequent, but important for maintaining genetically diverse stands. Here we investigate the molecular mechanisms involved in flowering of the seagrass Posidonia oceanica, an iconic species endemic to the Mediterranean. We generated a de novo transcriptome of this non-model species for leaf, male and female flower tissue of three individuals, and present molecular evidence for genes that may be involved in the flowering process and on the reproductive biology of the species. We present evidence that suggests that P. oceanica exhibits a strategy of protogyny, where the female part of the hermaphroditic flower develops before the male part, in order to avoid self-fertilization. We found photosynthetic genes to be up-regulated in the female flower tissues, indicating that this may be capable of photosynthesis. Finally, we detected a number of interesting genes, previously known to be involved in flowering pathways responding to light and temperature cues and in pathways involved in anthocyanin and exine synthesis. This first comparative transcriptomic approach of leaf, male and female tissue provides a basis for functional genomics research on flower development in P. oceanica and other seagrass species.

Transcriptome profiling of litchi leaves in response to low temperature reveals candidate regulatory genes and key metabolic events during floral induction

Background

Litchi (Litchi chinensis Sonn.) is an economically important evergreen fruit tree widely cultivated in subtropical areas. Low temperature is absolutely required for floral induction of litchi, but its molecular mechanism is not fully understood. Leaves of litchi played a key role during floral induction and could be the site of low temperature perception. Therefore, leaves were treated under different temperature (15 °C/25 °C), and high-throughput RNA sequencing (RNA-Seq) performed with leaf samples for the de novo assembly and digital gene expression (DGE) profiling analyses to investigate low temperature-induced gene expression changes.

Results

83,107 RNA-Seq unigenes were de novo assembled with a mean length of 1221 bp and approximately 61% of these unigenes (50,345) were annotated against public protein databases. Differentially-expressed genes (DEGs) under low temperature treatment in comparison with the control group were the main focus of our study. Hierarchical clustering analysis arranged 2755 DEGs into eight groups with three significant expression clusters (p-value ≤ 0.05) during floral induction. With the increasing contents of sugars and starch, the expression of genes involved in metabolism of sugars increased dramatically after low temperature induction. One FT gene (Unigene0025396, LcFT1) which produces a protein called ‘florigen’ was also detected among DEGs of litchi. LcFT1 exhibited an apparent specific tissue and its expression was highly increased after low temperature induction, GUS staining results also showed GUS activity driven by LcFT1 gene promoter can be induced by low temperature, which indicated LcFT1 probably played a pivotal role in the floral induction of litchi under low temperature.

Conclusions

Our study provides a global survey of transcriptomes to better understand the molecular mechanisms underlying changes of leaves in response to low temperature induction in litchi. The analyses of transcriptome profiles and physiological indicators will help us study the complicated metabolism of floral induction in the subtropic evergreen plants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3747-x) contains supplementary material, which is available to authorized users.