Comparative transcriptome analysis provides molecular insights into heterosis of waterlogging tolerance in Chrysanthemum indicum.

BACKGROUND: Heterosis breeding is one of the most important breeding methods for chrysanthemum. To date, the genetic mechanisms of heterosis for waterlogging tolerance in chrysanthemum are still unclear. This study aims to analyze the expression profiles and potential heterosis-related genes of two hybrid lines and their parents with extreme differences in waterlogging tolerance under control and waterlogging stress conditions by RNA-seq. RESULTS: A population of 140 F1 progeny derived from Chrysanthemum indicum (Nanchang) (waterlogging-tolerant) and Chrysanthemum indicum (Nanjing) (waterlogging-sensitive) was used to characterize the extent of genetic variation in terms of seven waterlogging tolerance-related traits across two years. Lines 98 and 95, respectively displaying positive and negative overdominance heterosis for the waterlogging tolerance traits together with their parents under control and waterlogging stress conditions, were used for RNA-seq. In consequence, the maximal number of differentially expressed genes (DEGs) occurred in line 98. Gene ontology (GO) enrichment analysis revealed multiple stress-related biological processes for the common up-regulated genes. Line 98 had a significant increase in non-additive genes under waterlogging stress, with transgressive up-regulation and paternal-expression dominant patterns being the major gene expression profiles. Further, GO analysis identified 55 and 95 transgressive up-regulation genes that overlapped with the up-regulated genes shared by two parents in terms of responses to stress and stimulus, respectively. 6,640 genes in total displaying maternal-expression dominance patterns were observed in line 95. In addition, 16 key candidate genes, including SAP12, DOX1, and ERF017 which might be of significant importance for the formation of waterlogging tolerance heterosis in line 98, were highlighted. CONCLUSION: The current study provides a comprehensive overview of the root transcriptomes among F1 hybrids and their parents under waterlogging stress. These findings lay the foundation for further studies on molecular mechanisms underlying chrysanthemum heterosis on waterlogging tolerance.

Flowering repressor CmSVP recruits the TOPLESS corepressor to control flowering in chrysanthemum.

Plant flowering time is induced by environmental and endogenous signals perceived by the plant. The MCM1-AGAMOUSDEFICIENS-Serum Response Factor-box (MADS-box) protein SHORT VEGETATIVE PHASE (SVP) is a pivotal repressor that negatively regulates the floral transition during the vegetative phase; however, the transcriptional regulatory mechanism remains poorly understood. Here, we report that CmSVP, a chrysanthemum (Chrysanthemum morifolium Ramat.) homolog of SVP, can repress the expression of a key flowering gene, a chrysanthemum FLOWERING LOCUS T-like gene (CmFTL3), by binding its promoter CArG element to delay flowering in the ambient temperature pathway in chrysanthemum. Protein-protein interaction assays identified an interaction between CmSVP and CmTPL1-2, a chrysanthemum homologue of TOPLESS (TPL) that plays critical roles as transcriptional corepressor in many aspects of plant life. Genetic analyses revealed the CmSVP-CmTPL1-2 transcriptional complex is a prerequisite for CmSVP to act as a floral repressor. Furthermore, overexpression of CmSVP rescued the phenotype of the svp-31 mutant in Arabidopsis (Arabidopsis thaliana), overexpression of AtSVP or CmSVP in the Arabidopsis dominant-negative mutation tpl-1 led to ineffective late flowering, and AtSVP interacted with AtTPL, confirming the conserved function of SVP in chrysanthemum and Arabidopsis. We have validated a conserved machinery wherein SVP partially relies on TPL to inhibit flowering via a thermosensory pathway.

Heterografting enhances chrysanthemums resistance to Alternaria alternata via jasmonate-mediated increases in trichomes and terpenoids.

Trichomes, specialized hair-like structures in the epidermal cells of the aboveground parts of plants, protect plants from pests and pathogens and produce valuable metabolites. Chrysanthemum morifolium, used in tea products, has ornamental and medicinal value. However, it is susceptible to Alternaria alternata fungal infection, posing a threat to its production and use, resulting in substantial economic losses. Increasing the density of glandular trichomes enhances disease resistance and improves the production of medicinal metabolites in chrysanthemums. Jasmonate (JA), promotes the formation of glandular trichomes in various plants. However, it remains unclear whether glandular trichome in chrysanthemums are regulated by JA. Grafting, a technique to improve plant resistance to biotic stresses, has been insufficiently explored in its impact on glandular trichomes, terpenoids, and disease resistance. In this study, we demonstrated that grafting with Artemisia vulgaris rootstocks improves the resistance of chrysanthemum scions to A. alternata. Heterografted chrysanthemums exhibited higher trichome density and terpenoid content compared to self-grafted counterparts. Transcriptome analysis highlighted the significant role of CmJAZ1-like in disease resistance in heterografted chrysanthemums. Overexpressing CmJAZ1-like lines exhibited sensitivity to A. alternate, characterized by reduced glandular trichome density and limited terpenoids. Conversely, silencing lines exhibited resistance to A. alternata showcasing increased glandular trichome density and abundant terpenoids. Higher JA content was confirmed in heterografted chrysanthemum scions compared to self-grafted ones. Furthermore, we established that JA promotes the development of glandular trichomes and the synthesis of terpenoids while inducing the degradation of CmJAZ1-like proteins in chrysanthemums. These findings suggest that higher JA increases trichome density and terpenoid content, enhancing resistance to A. alternata by regulating CmJAZ1-like in heterografted chrysanthemums.

A pattern for the early, middle, and late phase of tea chrysanthemum response to Fusarium oxysporum.

Chrysanthemum morifolium is cultivated worldwide and has high ornamental, tea, and medicinal value. With the increasing area of chrysanthemum cultivation and years of continuous cropping, Fusarium wilt disease frequently occurs in various production areas, seriously affecting the quality and yield and causing huge economic losses. However, the molecular response mechanism of Fusarium wilt infection remains unclear, which limits the molecular breeding process for disease resistance in chrysanthemums. In the present study, we analyzed the molecular response mechanisms of 'Huangju,' one of the tea chrysanthemum cultivars severely infested with Fusarium wilt in the field at the early, middle, and late phases of F. oxysporum infestation. 'Huangju' responded to the infestation mainly through galactose metabolism, plant-pathogen interaction, auxin, abscisic acid, and ethylene signalling in the early phase; galactose metabolism, plant-pathogen interaction, auxin, salicylic acid signal, and certain transcription factors (e.g., CmWRKY48) in the middle phase; and galactose metabolism in the late phase. Notably, the galactose metabolism was important in the early, middle, and late phases of 'Huangju' response to F. oxysporum. Meanwhile, the phytohormone auxin was involved in the early and middle responses. Furthermore, silencing of CmWRKY48 in 'Huangju' resulted in resistance to F. oxysporum. Our results revealed a new molecular pattern for chrysanthemum in response to Fusarium wilt in the early, middle, and late phases, providing a foundation for the molecular breeding of chrysanthemum for disease resistance.

Jasmonate signaling drives defense responses against Alternaria alternata in chrysanthemum.

BACKGROUND: Black spot disease caused by the necrotrophic fungus Alternaria spp. is one of the most devastating diseases affecting Chrysanthemum morifolium. There is currently no effective way to prevent chrysanthemum black spot. RESULTS: We revealed that pre-treatment of chrysanthemum leaves with the methy jasmonate (MeJA) significantly reduces their susceptibility to Alternaria alternata. To understand how MeJA treatment induces resistance, we monitored the dynamics of metabolites and the transcriptome in leaves after MeJA treatment following A. alternata infection. JA signaling affected the resistance of plants to pathogens through cell wall modification, Ca2+ regulation, reactive oxygen species (ROS) regulation, mitogen-activated protein kinase cascade and hormonal signaling processes, and the accumulation of anti-fungal and anti-oxidant metabolites. Furthermore, the expression of genes associated with these functions was verified by reverse transcription quantitative PCR and transgenic assays. CONCLUSION: Our findings indicate that MeJA pre-treatment could be a potential orchestrator of a broad-spectrum defense response that may help establish an ecologically friendly pest control strategy and offer a promising way of priming plants to induce defense responses against A. alternata.

Potential pathways and genes expressed in Chrysanthemum in response to early fusarium oxysporum infection.

BACKGROUND: Chrysanthemum Fusarium wilt is a common fungal disease caused by Fusarium oxysporum, which causes continuous cropping obstacles and huge losses to the chrysanthemum industry. The defense mechanism of chrysanthemum against F. oxysporum remains unclear, especially during the early stages of the disease. Therefore, in the present study, we analyzed chrysanthemum 'Jinba' samples inoculated with F. oxysporum at 0, 3, and 72 h using RNA-seq. RESULTS: The results revealed that 7985 differentially expressed genes (DEGs) were co-expressed at 3 and 72 h after F. oxysporum infection. We analyzed the identified DEGs using Kyoto Encyclopedia of Genes and Genomes and Gene Ontology. The DEGs were primarily enriched in "Plant pathogen interaction", "MAPK signaling pathway", "Starch and sucrose metabolism", and "Biosynthesis of secondary metabolites". Genes related to the synthesis of secondary metabolites were upregulated in chrysanthemum early during the inoculation period. Furthermore, peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase enzymes were consistently produced to accumulate large amounts of phenolic compounds to resist F. oxysporum infection. Additionally, genes related to the proline metabolic pathway were upregulated, and proline levels accumulated within 72 h, regulating osmotic balance in chrysanthemum. Notably, the soluble sugar content in chrysanthemum decreased early during the inoculation period; we speculate that this is a self-protective mechanism of chrysanthemums for inhibiting fungal reproduction by reducing the sugar content in vivo. In the meantime, we screened for transcription factors that respond to F. oxysporum at an early stage and analyzed the relationship between WRKY and DEGs in the "Plant-pathogen interaction" pathway. We screened a key WRKY as a research target for subsequent experiments. CONCLUSION: This study revealed the relevant physiological responses and gene expression changes in chrysanthemum in response to F. oxysporum infection, and provided a relevant candidate gene pool for subsequent studies on chrysanthemum Fusarium wilt.

Transcription factor CmbHLH16 regulates petal anthocyanin homeostasis under different lights in Chrysanthemum.

Light is essential to plant survival and elicits a wide range of plant developmental and physiological responses under different light conditions. A low red-to-far red (R/FR) light ratio induces shade-avoidance responses, including decreased anthocyanin accumulation, whereas a high R/FR light ratio promotes anthocyanin biosynthesis. However, the detailed molecular mechanism underpinning how different R/FR light ratios regulate anthocyanin homeostasis remains elusive, especially in non-model species. Here, we demonstrate that a low R/FR light ratio induced the expression of CmMYB4, which suppressed the anthocyanin activator complex CmMYB6-CmbHLH2, leading to the reduction of anthocyanin accumulation in Chrysanthemum (Chrysanthemum morifolium) petals. Specifically, CmMYB4 recruited the corepressor CmTPL (TOPLESS) to directly bind the CmbHLH2 promoter and suppressed its transcription by impairing histone H3 acetylation. Moreover, the low R/FR light ratio inhibited the PHYTOCHROME INTERACTING FACTOR family transcription factor CmbHLH16, which can competitively bind to CmMYB4 and destabilize the CmMYB4-CmTPL protein complex. Under the high R/FR light ratio, CmbHLH16 was upregulated, which impeded the formation of the CmMYB4-CmTPL complex and released the suppression of CmbHLH2, thus promoting anthocyanin accumulation in Chrysanthemum petals. Our findings reveal a mechanism by which different R/FR light ratios fine-tune anthocyanin homeostasis in flower petals.

Overexpression of CmWRKY8-1-VP64 Fusion Protein Reduces Resistance in Response to Fusarium oxysporum by Modulating the Salicylic Acid Signaling Pathway in Chrysanthemum morifolium.

Chrysanthemum Fusarium wilt, caused by the pathogenic fungus Fusarium oxysporum, severely reduces ornamental quality and yields. WRKY transcription factors are extensively involved in regulating disease resistance pathways in a variety of plants; however, it is unclear how members of this family regulate the defense against Fusarium wilt in chrysanthemums. In this study, we characterized the WRKY family gene CmWRKY8-1 from the chrysanthemum cultivar 'Jinba', which is localized to the nucleus and has no transcriptional activity. We obtained CmWRKY8-1 transgenic chrysanthemum lines overexpressing the CmWRKY8-1-VP64 fusion protein that showed less resistance to F. oxysporum. Compared to Wild Type (WT) lines, CmWRKY8-1 transgenic lines had lower endogenous salicylic acid (SA) content and expressed levels of SA-related genes. RNA-Seq analysis of the WT and CmWRKY8-1-VP64 transgenic lines revealed some differentially expressed genes (DEGs) involved in the SA signaling pathway, such as PAL, AIM1, NPR1, and EDS1. Based on Gene Ontology (GO) enrichment analysis, the SA-associated pathways were enriched. Our results showed that CmWRKY8-1-VP64 transgenic lines reduced the resistance to F. oxysporum by regulating the expression of genes related to the SA signaling pathway. This study demonstrated the role of CmWRKY8-1 in response to F. oxysporum, which provides a basis for revealing the molecular regulatory mechanism of the WRKY response to F. oxysporum infestation in chrysanthemum.

Long-distance transport RNAs between rootstocks and scions and graft hybridization.

MAIN CONCLUSION: The present review addresses the advances of the identification methods, functions, and transportation mechanism of long-distance transport RNAs between rootstock and scion. In addition, we highlight the cognitive processes and potential mechanisms of graft hybridization. Phloem, the main transport channel of higher plants, plays an important role in the growth and development of plants. Numerous studies have identified a large number of RNAs, including mRNAs, miRNAs, siRNAs, and lncRNAs, in the plant phloem. They can not only be transported to long distances across the grafting junction in the phloem, but also act as signal molecules to regulate the growth, development, and stress resistance of remote cells or tissues, resulting in changes in the traits of rootstocks and scions. Many mobile RNAs have been discovered, but their detection methods, functions, and long-distance transport mechanisms remain to be elucidated. In addition, grafting hybridization, a phenomenon that has been questioned before, and which has an important role in selecting for superior traits, is gradually being recognized with the emergence of new evidence and the prevalence of horizontal gene transfer between parasitic plants. In this review, we outline the species, functions, identification methods, and potential mechanisms of long-distance transport RNAs between rootstocks and scions after grafting. In addition, we summarize the process of recognition and the potential mechanisms of graft hybridization. This study aimed to emphasize the role of grafting in the study of long-distance signals and selection for superior traits and to provide ideas and clues for further research on long-distance transport RNAs and graft hybridization.

Dual species dynamic transcripts reveal the interaction mechanisms between Chrysanthemum morifolium and Alternaria alternata.

BACKGROUND: Chrysanthemum (Chrysanthemum morifolium) black spot disease caused by Alternaria alternata is one of the plant's most destructive diseases. Dual RNA-seq was performed to simultaneously assess their transcriptomes to analyze the potential interaction mechanism between the two species, i.e., host and pathogen. RESULTS: C. morifolium and A. alternata were subjected to dual RNA-seq at 1, 12, and 24 h after inoculation, and differential expression genes (DEGs) in both species were identified. This analysis confirmed 153,532 DEGs in chrysanthemum and 14,932 DEGs in A. alternata, which were involved in plant-fungal interactions and phytohormone signaling. Fungal DEGs such as toxin synthesis related enzyme and cell wall degrading enzyme genes played important roles during chrysanthemum infection. Moreover, a series of key genes highly correlated with the early, middle, or late infection stage were identified, together with the regulatory network of key genes annotated in the Plant Resistance Genes database (PRGdb) or Pathogen-Host Interactions database (PHI-base). Highly correlated genes were identified at the late infection stage, expanding our understanding of the interplay between C. morifolium and A. alternata. Additionally, six DEGs each from chrysanthemum and A. alternata were selected for quantitative real-time PCR (qRT-PCR) assays to validate the RNA-seq output. CONCLUSIONS: Collectively, data obtained in this study enriches the resources available for research into the interactions that exist between chrysanthemum and A. alternata, thereby providing a theoretical basis for the development of new chrysanthemum cultivars with resistance to pathogen.

Identification of 5S and 45S rDNA sites in Chrysanthemum species by using oligonucleotide fluorescence in situ hybridization (Oligo-FISH).

Fluorescence in situ hybridization (FISH) is a conventional method used to visualize the distribution of DNA elements within a genome. To examine the relationships within the Chrysanthemum genus, ribosomal DNA (rDNA), a popular cytogenetic marker, was utilized as a probe for FISH within this genus. Based on the genome data of Chrysanthemum nankingense, C. seticuspe and its allied genera in the Compositae(Asteraceae), we explored rDNA sequences to design oligonucleotide probes and perform oligonucleotide fluorescence in situ hybridization (Oligo-FISH) in eight Chrysanthemum accessions. The results showed that the majority of 5S rDNA signals were located in subterminal chromosome regions and that the number of 5S rDNA sites might be tightly associated with ploidy. For 45S rDNA sites, the number and intensity of signals differed from those of previously investigated Chrysanthemum resources. These findings may provide an optimally reliable method of examining the chromosome composition and structural variation of Chrysanthemum and its related species and allow researchers to understand the evolutionary history and phylogenetic relationships of Chrysanthemum.

CmBBX8 accelerates flowering by targeting CmFTL1 directly in summer chrysanthemum.

For a flowering plant, the transition from vegetative stage to reproductive growth is probably the most critical developmental switch. In the model plant Arabidopsis thaliana, the product of BBX7, group II member of BBX family, acts to delay floral transition. In this study, a presumed chrysanthemum homolog of a second group gene AtBBX8, designated CmBBX8, had been isolated and characterized. The transcription of CmBBX8 followed a diurnal rhythm as the chrysanthemum floral transition regulator. Overexpression of CmBBX8 accelerated flowering, while its (artificial microRNAs) amiR-enabled knockdown delayed flowering in plants grown under both long- and short-day conditions. Global expression analysis revealed that genes associated with photoperiod were down-regulated in amiR-CmBBX8 lines compared with the wild type, which were verified to be up-regulated in overexpressing lines (OX-CmBBX8) by RT-PCR. A number of in vitro assays were used to show that CmBBX8 targets CmFTL1. Furthermore, the function of CmFTL1 as a floral inducer under long-day conditions was confirmed by the behaviour of engineered summer-flowering chrysanthemum plants. The conclusion is that the BBX8-FT regulatory module is an important determinant of reproductive development in summer-flowering chrysanthemum.

Identification of favorable SNP alleles and candidate genes responsible for inflorescence-related traits via GWAS in chrysanthemum.

KEY MESSAGE: 81 SNPs were identified for three inflorescence-related traits, in which 15 were highly favorable. Two dCAPS markers were developed for future MAS breeding, and six candidate genes were predicted. Chrysanthemum is a leading ornamental species worldwide and demonstrates a wealth of morphological variation. Knowledge about the genetic basis of its phenotypic variation for key horticultural traits can contribute to its effective management and genetic improvement. In this study, we conducted a genome-wide association study (GWAS) based on two years of phenotype data and a set of 92,617 single nucleotide polymorphisms (SNPs) using a panel of 107 diverse cut chrysanthemums to dissect the genetic control of three inflorescence-related traits. A total of 81 SNPs were significantly associated with the three inflorescence-related traits (capitulum diameter, number of ray florets and flowering time) in at least one environment, with an individual allele explaining 22.72-38.67% of the phenotypic variation. Fifteen highly favorable alleles were identified for the three target traits by computing the phenotypic effect values for the stable associations detected in 2 year-long trials at each locus. Dosage pyramiding effects of the highly favorable SNP alleles and significant linear correlations between highly favorable allele numbers and corresponding phenotypic performance were observed. Two highly favorable SNP alleles correlating to flowering time and capitulum diameter were converted to derived cleaved amplified polymorphic sequence (dCAPS) markers to facilitate future breeding. Finally, six putative candidate genes were identified that contribute to flowering time and capitulum diameter. These results serve as a foundation for analyzing the genetic mechanisms underlying important horticultural traits and provide valuable insights into molecular marker-assisted selection (MAS) in chrysanthemum breeding programs.

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.

The heterologous expression of CmBBX22 delays leaf senescence and improves drought tolerance in Arabidopsis.

KEY MESSAGE: CmBBX22, a transcription factor of chrysanthemum, was verified to confer drought tolerance in Arabidopsis thaliana. The BBX proteins are known to operate as regulators of plant growth and development, but as yet their contribution to the abiotic stress response has not been well defined. Here, the chrysanthemum BBX family member CmBBX22, an ortholog of AtBBX22, was found to be transcribed throughout the plant, although at varying intensity, and was induced by imposing moisture deficiency via exposure to polyethylene glycol. The heterologous, constitutive expression of this gene in Arabidopsis thaliana compromised germination and seedling growth, but enhanced the plants' ability to tolerate drought stress. In transgenic plants challenged with abscisic acid, leaf senescence was delayed and the senescence-associated genes and chlorophyll catabolic genes SAG29, NYE1, NYE2 and NYC1 were down-regulated. We speculated that CmBBX22 may serves as a regulator in mediating drought stress tolerance and delaying leaf senescence.

The Heterologous Expression of a Chrysanthemum nankingense TCP Transcription Factor Blocks Cell Division in Yeast and Arabidopsis thaliana.

Both the presence of, and the important contribution to growth and development made by TCP transcription factors, have been established in various plant species. Here, a TCP4 homolog isolated from Chrysanthemum nankingense was shown to be more strongly transcribed in the diploid than in the autotetraploid form of the species. CnTCP4 was shown to encode a member of the class II TCP family and to be transcribed most strongly in the leaf and ligulate flowers. Its transcription was found to be substantially inhibited by spraying the plant with the synthetic cytokinin 6-benzylaminopurine. The transient expression of CnTCP4 in onion epidermal cells showed that its product localized to the nucleus, and a yeast one hybrid assay suggested that its product had transcriptional activation ability. The constitutive expression of CnTCP4 in fission yeast suppressed cell proliferation, inducing the formation of longer and a higher frequency of multinuclated cells. Its constitutive expression in Arabidopsis thaliana reduced the size of the leaves. The presence of the transgene altered the transcription of a number of cell division-related genes. A yeast one hybrid assay identified a second TCP gene (CnTCP2) able to interact with the CnTCP4 promoter. A transient expression experiment in Nicotiana benthamiana leaves showed that CnTCP2 was able to activate the CnTCP4 promoter. Like CnTCP4, CnTCP2 was shown to encode a member of the class II TCP family, to be transcribed most strongly in the leaf and ligulate flowers, and to be suppressed by exogenous 6-benzylaminopurine treatment. The CnTCP2 protein also localized to the nucleus, but had no transcriptional activation ability. Its constitutive expression in A. thaliana had similar phenotypic consequences to those induced by CnTCP4.

Over-expression of chrysanthemum CmDREB6 enhanced tolerance of chrysanthemum to heat stress.

BACKGROUND: Chrysanthemum is among the top ten traditional flowers in China, and one of the four major cut flowers in the world, but the growth of chrysanthemum is severely restricted by high temperatures which retard growth and cause defects in flowers. DREB (dehydration-responsive element-binding) transcription factors play important roles in the response to abiotic and biotic stresses. However, whether the DREB A-6 subgroup is involved in heat tolerance has not been reported conclusively. RESULT: In the present study, CmDREB6 was cloned from chrysanthemum (Chrysanthemum morifolium) 'Jinba'. CmDREB6, containing a typical AP2/ERF domain, was classed into the DREB A-6 subgroup and shared highest homology with Cichorium intybus L. CiDREB6 (73%). CmDREB6 was expressed at its highest levels in the leaf. The CmDREB6 protein localized to the nucleus. Based on the yeast one hybrid assay, CmDREB6 showed transcription activation activity in yeast, and the transcriptional activation domain was located in the 3 'end ranging from 230 to 289 amino acids residues. CmDREB6 overexpression enhanced the tolerance of chrysanthemum to heat. The survival rate of two transgenic lines was as high as 85%, 50%, respectively, in contrast to 3.8% of wild-type (WT). Over-expression of CmDREB6 promoted the expression of CmHsfA4, CmHSP90, and the active oxygen scavenging genes CmSOD and CmCAT. CONCLUSION: In this study, DREB A-6 subgroup gene CmDREB6 was cloned from chrysanthemum 'Jinba'. Overexpression of CmDREB6 enhanced heat tolerance of chrysanthemum by regulating genes involved in the heat shock response and ROS homeogenesis.

Dynamic and epistatic QTL mapping reveals the complex genetic architecture of waterlogging tolerance in chrysanthemum.

MAIN CONCLUSION: 37 unconditional QTLs, 51 conditional QTLs and considerable epistatic QTLs were detected for waterlogging tolerance, and six favourable combinations were selected accelerating the possible application of MAS in chrysanthemum breeding. Chrysanthemum is seriously impacted by soil waterlogging. To determine the genetic characteristics of waterlogging tolerance (WAT) in chrysanthemum, a population of 162 F1 lines was used to construct a genetic map to identify the dynamic and epistatic quantitative trait loci (QTLs) for four WAT traits: wilting index (WI), dead leaf ratio (DLR), chlorosis score (Score) and membership function value of waterlogging (MFVW). The h B2 for the WAT traits ranged from 0.49 to 0.64, and transgressive segregation was observed in both directions. A total of 37 unconditional consensus QTLs with 5.81-18.21% phenotypic variation explanation (PVE) and 51 conditional consensus QTLs with 5.90-24.56% PVE were detected. Interestingly, three unconditional consensus QTLs were consistently identified across different stages, whereas no conditional consensus QTLs were consistently expressed. In addition, considerable epistatic QTLs, all with PVE values ranging from 0.01 to 8.87%, were detected by a joint analysis of WAT phenotypes. These results illustrated that the QTLs (genes) controlling WAT were environmentally dependent and selectively expressed at different times and indicated that both additive and epistatic effects underlie the inheritance of WAT in chrysanthemum. The findings of the current study provide insights into the complex genetic architecture of WAT, and the identification of favourable alleles represents an important step towards the application of molecular marker-assisted selection (MAS) and QTL pyramiding in chrysanthemum WAT breeding programmes.

GC-MS Analysis of the Volatile Constituents in the Leaves of 14 Compositae Plants.

The green organs, especially the leaves, of many Compositae plants possess characteristic aromas. To exploit the utility value of these germplasm resources, the constituents, mainly volatile compounds, in the leaves of 14 scented plant materials were qualitatively and quantitatively compared via gas chromatography-mass spectrometry (GC-MS). A total of 213 constituents were detected and tentatively identified in the leaf extracts, and terpenoids (especially monoterpene and sesquiterpene derivatives), accounting for 40.45-90.38% of the total compounds, were the main components. The quantitative results revealed diverse concentrations and compositions of the chemical constituents between species. Principal component analysis (PCA) showed that different groups of these Compositae plants were characterized by main components of α-thujone, germacrene D, eucalyptol, ß-caryophyllene, and camphor, for example. On the other hand, cluster memberships corresponding to the molecular phylogenetic framework, were found by hierarchical cluster analysis (HCA) based on the terpenoid composition of the tested species. These results provide a phytochemical foundation for the use of these scented Compositae plants, and for the further study of the chemotaxonomy and differential metabolism of Compositae species.

Whole genome duplication enhances the photosynthetic capacity of Chrysanthemum nankingense.

Whole genome duplication has a major effect on the phenotype and physiology of higher plants. A comparison between the diploid and tetraploid forms of Chrysanthemum nankingense showed that the latter's leaf contained a higher content of chlorophyll a/b and harbored a larger number of chloroplasts per cell, leading to an enhancement in its photosynthetic capacity and an improved level of productivity with respect to biomass. A transcriptomic analysis of the two ploidy level forms revealed 21,559 differentially transcribed genes. Compared with diploid progenitor, a number of genes associated with chlorophyll synthesis and those encoding components of photosystems I and II were up-regulated in the tetraploid form, while those associated with chlorophyll degradation were down-regulated. These results indicated that whole genome duplication can directly affect chlorophyll synthesis/degradation and photosynthesis pathways associated with plant growth ratio and biomass accumulation.