CmCYC2-like transcription factors may interact with each other or bind to the promoter to regulate floral symmetry development in Chrysanthemum morifolium

Genome-wide identification and characterization of TCP gene family in Dendrobium nobile and their role in perianth development

TCP is a widely distributed, essential plant transcription factor that regulates plant growth and development. An in-depth study of TCP genes in Dendrobium nobile, a crucial parent in genetic breeding and an excellent model material to explore perianth development in Dendrobium, has not been conducted. We identified 23 DnTCP genes unevenly distributed across 19 chromosomes and classified them as Class I PCF (12 members), Class II: CIN (10 members), and CYC/TB1 (1 member) based on the conserved domain and phylogenetic analysis. Most DnTCPs in the same subclade had similar gene and motif structures. Segmental duplication was the predominant duplication event for TCP genes, and no tandem duplication was observed. Seven genes in the CIN subclade had potential miR319 and -159 target sites. Cis-acting element analysis showed that most DnTCP genes contained many developmental stress-, light-, and phytohormone-responsive elements in their promoter regions. Distinct expression patterns were observed among the 23 DnTCP genes, suggesting that these genes have diverse regulatory roles at different stages of perianth development or in different organs. For instance, DnTCP4 and DnTCP18 play a role in early perianth development, and DnTCP5 and DnTCP10 are significantly expressed during late perianth development. DnTCP17, 20, 21, and 22 are the most likely to be involved in perianth and leaf development. DnTCP11 was significantly expressed in the gynandrium. Specially, MADS-specific binding sites were present in most DnTCP genes putative promoters, and two Class I DnTCPs were in the nucleus and interacted with each other or with the MADS-box. The interactions between TCP and the MADS-box have been described for the first time in orchids, which broadens our understanding of the regulatory network of TCP involved in perianth development in orchids.

Identification and characterization of CYC2-like genes related to floral symmetric development in Tagetes erecta (Asteraceae)

Marigold (Tagetes erecta) is an annual herbaceous flower belonging to Asteraceae, whose capitulum is composed of bilateral symmetry ray florets on the outer periphery and radial symmetry disk florets on the inside. The flower symmetry evolution from radial symmetry to bilateral symmetry has changed the morphology, inflorescence architecture and function of florets among several lineages in Asteraceae. Several studies have identified that CYC2 genes in TCP transcription factor family are the key genes regulating the flower morphogenesis, such as corolla symmetry and stamen development. Here, seven TeCYC2 genes were cloned and phylogenetically grouped into the CYC2 branch of TCP transcription family. TeCYC2c and TeCYC2d were found to be expressed specifically in ray florets, TeCYC2b was strongly expressed in both ray and disk florets, TeCYC2g was significantly higher expressed in ray florets than in disk florets, while TeCYC2a, TeCYC2e1 and TeCYC2e2 were significantly expressed in disk florets, according to an examination of the expression profile. Among the ectopic expression lines of seven TeCYC2 genes in Arabidopsis thaliana, the flower symmetry of all transgenic lines was changed from radial symmetry to bilateral symmetry, and only the reproductive growth of TeCYC2c lines was affected. In TeCYC2c transgenic Arabidopsis, the pollen sac was difficult to crack, and the filaments were shorter than the pistils, resulting in a significant decrease in the seed setting rate. All TeCYC2 proteins were localized in the nucleus. Eight pairs of interactions between TeCYC2 proteins were validated by Y2H and BiFC assays, indicating the possibility of TeCYC2 proteins forming homodimers or heterodimers to improve functional specificity. Our findings verified the main regulatory role of TeCYC2c on the development of corollas and stamen in marigold, and analyzed the interaction network of the formation mechanism of floral symmetry in two florets, which provided more insights into the expansion of CYC2 genes in the evolution of Asteraceae inflorescence and contributed to elucidate the complex regulatory network, as well as the molecular breeding concerning flower form diversity in marigold.

Designing of future ornamental crops: a biotechnological driven perspective

With a basis in human appreciation of beauty and aesthetic values, the new era of ornamental crops is based on implementing innovative technologies and transforming symbols into tangible assets. Recent advances in plant biotechnology have attracted considerable scientific and industrial interest, particularly in terms of modifying desired plant traits and developing future ornamental crops. By utilizing omics approaches, genomic data, genetic engineering, and gene editing tools, scientists have successively explored the underlying molecular mechanism and potential gene(s) behind trait regulation such as floral induction, plant architecture, stress resistance, plasticity, adaptation, and phytoremediation in ornamental crop species. These signs of progress lay a theoretical and practical foundation for designing and enhancing the efficiency of ornamental plants for a wide range of applications. In this review, we briefly summarized the existing literature and advances in biotechnological approaches for the improvement of vital traits in ornamental plants. The future ornamental plants, such as light-emitting plants, biotic/abiotic stress detectors, and pollution abatement, and the introduction of new ornamental varieties via domestication of wild species are also discussed.

Morphological Characteristics and Expression Patterns of CmCYC2c of Different Flower Shapes in Chrysanthemum morifolium

The chrysanthemum is widely used as a cut flower, potted flower, and garden flower worldwide and has high ornamental, edible, and medicinal value. The flower heads, composed of ray florets and disc florets, are the most diverse in terms of morphology among ornamental plants. Here, we compared and analyzed the developmental processes of different capitulum types as well as ray florets and disc florets. Morphological differentiation of the two florets occurred on the dorsal domain of the petals at stage Ⅳ of flower development, and differences in stamen development occurred at stage Ⅴ. The dorsal domain of the ray florets and the early stage of flower development were also an essential site and period, respectively, for the differences among capitulum types. In situ hybridization revealed that CmCYC2c, whose homologs are involved in the specification of floret identity in Asteraceae, was expressed in both the dorsal and ventral domains of the ray petals in the tubular-type chrysanthemum, whereas, it was differentially transcribed in the ray petals of flat- and spoon-type chrysanthemum cultivars and had lower or no expression in the dorsal domain and higher expression in the ventral domain at stage Ⅳ. Our study indicates that the expression pattern of CmCYC2c on the dorsal domain of the ray floret at stage Ⅳ contributes to the formation of diverse flower head types in chrysanthemums.

Genome-wide identification of the TCP gene family in Chrysanthemum lavandulifolium and its homologs expression patterns during flower development in different Chrysanthemum species

TCP proteins, part of the transcription factors specific to plants, are recognized for their involvement in various aspects of plant growth and development. Nevertheless, a thorough investigation of TCPs in Chrysanthemum lavandulifolium, a prominent ancestral species of cultivated chrysanthemum and an excellent model material for investigating ray floret (RF) and disc floret (DF) development in Chrysanthemum, remains unexplored yet. Herein, a comprehensive study was performed to analyze the genome-wide distribution of TCPs in C. lavandulifolium. In total, 39 TCPs in C. lavandulifolium were identified, showing uneven distribution on 8 chromosomes. Phylogenetic and gene structural analyses revealed that ClTCPs were grouped into classes I and II. The class II genes were subdivided into two subclades, the CIN and CYC/TB1 subclades, with members of each clade having similar conserved motifs and gene structures. Four CIN subclade genes (ClTCP24, ClTCP25, ClTCP26, and ClTCP27) contained the potential miR319 target sites. Promoter analysis revealed that ClTCPs had numerous cis-regulatory elements associated with phytohormone responses, stress responses, and plant growth/development. The expression patterns of ClTCPs during capitulum development and in two different florets were determined using RNA-seq and qRT-PCR. The expression levels of TCPs varied in six development stages of capitula; 25 out of the 36 TCPs genes were specifically expressed in flowers. Additionally, we identified six key ClCYC2 genes, which belong to the class II TCP subclade, with markedly upregulated expression in RFs compared with DFs, and these genes exhibited similar expression patterns in the two florets of Chrysanthemum species. It is speculated that they may be responsible for RFs and DFs development. Subcellular localization and transactivation activity analyses of six candidate genes demonstrated that all of them were localized in the nucleus, while three exhibited self-activation activities. This research provided a better understanding of TCPs in C. lavandulifolium and laid a foundation for unraveling the mechanism by which important TCPs involved in the capitulum development.

Genome-wide identification and analysis of TCP family genes in Medicago sativa reveal their critical roles in Na+/K+ homeostasis

BACKGROUND

Medicago sativa is the most important forage world widely, and is characterized by high quality and large biomass. While abiotic factors such as salt stress can negatively impact the growth and productivity of alfalfa. Maintaining Na⁺/K⁺ homeostasis in the cytoplasm helps reduce cell damage and nutritional deprivation, which increases a salt-tolerance of plant. Teosinte Branched1/ Cycloidea/ Proliferating cell factors (TCP) family genes, a group of plant-specific transcription factors (TFs), involved in regulating plant growth and development and abiotic stresses. Recent studies have shown TCPs control the Na⁺/K⁺ concentration of plants during salt stress. In order to improve alfalfa salt tolerance, it is important to identify alfalfa TCP genes and investigate if and how they regulate alfalfa Na⁺/K⁺ homeostasis.

RESULTS

Seventy-one MsTCPs including 23 non-redundant TCP genes were identified in the database of alfalfa genome (C.V XinJiangDaYe), they were classified into class I PCF (37 members) and class II: CIN (28 members) and CYC/TB1 (9 members). Their distribution on chromosome were unequally. MsTCPs belonging to PCF were expressed specifically in different organs without regularity, which belonging to CIN class were mainly expressed in mature leaves. MsTCPs belongs to CYC/TB1 clade had the highest expression level at meristem. Cis-elements in the promoter of MsTCPs were also predicted, the results indicated that most of the MsTCPs will be induced by phytohormone and stress treatments, especially by ABA-related stimulus including salinity stress. We found 20 out of 23 MsTCPs were up-regulated in 200 mM NaCl treatment, and MsTCP3/14/15/18 were significantly induced by 10 μM KCl, a K⁺ deficiency treatment. Fourteen non-redundant MsTCPs contained miR319 target site, 11 of them were upregulated in MIM319 transgenic alfalfa, and among them four (MsTCP3/4/10A/B) genes were directly degraded by miR319. MIM319 transgene alfalfa plants showed a salt sensitive phenotype, which caused by a lower content of potassium in alfalfa at least partly. The expression of potassium transported related genes showed significantly higher expression in MIM319 plants.

CONCLUSIONS

We systematically analyzes the MsTCP gene family at a genome-wide level and reported that miR319-TCPs model played a function in K⁺ up-taking and/ or transportation especially in salt stress. The study provide valuable information for future study of TCP genes in alfalfa and supplies candidate genes for salt-tolerance alfalfa molecular-assisted breeding.

Advances in Research on the Regulation of Floral Development by CYC-like Genes

CYCLOIDEA (CYC)-like genes belong to the TCP transcription factor family and play important roles associated with flower development. The CYC-like genes in the CYC1, CYC2, and CYC3 clades resulted from gene duplication events. The CYC2 clade includes the largest number of members that are crucial regulators of floral symmetry. To date, studies on CYC-like genes have mainly focused on plants with actinomorphic and zygomorphic flowers, including Fabaceae, Asteraceae, Scrophulariaceae, and Gesneriaceae species and the effects of CYC-like gene duplication events and diverse spatiotemporal expression patterns on flower development. The CYC-like genes generally affect petal morphological characteristics and stamen development, as well as stem and leaf growth, flower differentiation and development, and branching in most angiosperms. As the relevant research scope has expanded, studies have increasingly focused on the molecular mechanisms regulating CYC-like genes with different functions related to flower development and the phylogenetic relationships among these genes. We summarize the status of research on the CYC-like genes in angiosperms, such as the limited research conducted on CYC1 and CYC3 clade members, the necessity to functionally characterize the CYC-like genes in more plant groups, the need for investigation of the regulatory elements upstream of CYC-like genes, and exploration of the phylogenetic relationships and expression of CYC-like genes with new techniques and methods. This review provides theoretical guidance and ideas for future research on CYC-like genes.

Genetic control of the lateral petal shape and identity of asymmetric flowers in mungbean (Vigna radiata L.)

Broad diversity of flowers in Fabaceae provides a good system to investigate development and evolution of floral symmetry in higher plants. Many studies have demonstrated a conserved mechanism controlling development of zygomorphic flower during last decades. However, the molecular basis of how asymmetric flower established is largely unknown. In this study, we characterized mutants named keeled wings (kw) in mungbean (Vigna radiata L.), which is a legume species with asymmetric flowers. Compared to those in the wild type plants, the lateral petals were ventralized in the kw mutants. Map-based cloning showed that KW was VrCYC3 gene in mungbean, the ortholog of Lotus japonicus CYC3 (LjCYC3) and Pisum sativum CYC3 (PsCYC3). In addition, another two CYC-like genes named VrCYC1 and VrCYC2 were identified from mungbean genome. The three CYC-like genes displayed distinct expression patterns in dorsal, lateral and ventral petals. It was found that VrCYC3 was located in nucleus. Further analysis showed that VrCYC3 had transcription activity and could interact with VrCYC1 and VrCYC2 in yeast cell. Moreover, the deletion of two amino acid residues in the R domain of VrCYC3 protein could decrease its interaction with VrCYC1 and VrCYC2 proteins. Our results suggest that LjCYC3/VrCYC3 orthologs play conserved roles determining the lateral petal shape and identity of zygomorphic flower as well as asymmetric flower in Papilionoideae.

A Transcription Factor SlNAC10 Gene of Suaeda liaotungensis Regulates Proline Synthesis and Enhances Salt and Drought Tolerance

The NAC (NAM, ATAF1/2, and CUC2) transcription factors are one of the largest families of transcription factors in plants and play an important role in plant development and the response to adversity. In this study, we cloned a new NAC gene, SlNAC10, from the halophyte Suaeda liaotungensis K. The gene has a total length of 1584 bp including a complete ORF of 1107 bp that encodes 369 amino acids. The SlNAC10-GFP fusion protein is located in the nucleus and SlNAC10 has a transcription activation structural domain at the C-terminus. We studied the expression characteristics of SlNAC10 and found that it was highest in the leaves of S. liaotungensis and induced by drought, salt, cold, and abscisic acid (ABA). To analyze the function of SlNAC10 in plants, we obtained SlNAC10 transgenic Arabidopsis. The growth characteristics and physiological indicators of transgenic Arabidopsis were measured under salt and drought stress. The transgenic Arabidopsis showed obvious advantages in the root length and survival rate; chlorophyll fluorescence levels; and the antioxidant enzyme superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, and the proline content was higher than that of the wild-type (WT) Arabidopsis, whereas the relative electrolyte leakage and malondialdehyde (MDA) content were lower than those of the wild-type Arabidopsis. We explored the regulatory role of SlNAC10 on proline synthesis-related enzyme genes and found that SlNAC10 binds to the AtP5CS1, AtP5CS2, and AtP5CR promoters and regulates their downstream gene transcription. To sum up, SlNAC10 as a transcription factor improves salt and drought tolerance in plants possibly by regulating proline synthesis.

CmBES1 is a regulator of boundary formation in chrysanthemum ray florets

Chrysanthemum (Chrysanthemum morifolium) is an ideal model species for studying petal morphogenesis because of the diversity in the flower form across varieties; however, the molecular mechanisms underlying petal development are poorly understood. Here, we show that the brassinosteroid transcription factor BRI1-EMS-SUPPRESSOR 1 (CmBES1) in chrysanthemum (C. morifolium cv. Jinba) is important for organ boundary formation because it represses organ boundary identity genes. Chrysanthemum plants overexpressing CmBES1 displayed increased fusion of the outermost ray florets due to the loss of differentiation of the two dorsal petals, which developed simultaneously with the ventral petals. RNA-seq analysis of the overexpression lines revealed potential genes and pathways involved in petal development, such as CUP-SHAPED COTYLEDON (CUC2), CYCLOIDEA 4 (CYC4), genes encoding MADS-box transcription factors and homeodomain-leucine zippers (HD-Zips) and auxin pathway-related genes. This study characterizes the role of CmBES1 in ray floret development by its modulation of flower development and boundary identity genes in chrysanthemum.