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Abstract Background Chrysanthemum (Chrysanthemum × morifolium) is one of the four major cut flowers worldwide and is valued for ornamental, culinary, and medicinal purposes. Terpenoids are key components of the fragrance of chrysanthemum; they not only serve to repel insect herbivores and promote pollination but also impact the value of the plant. However, the terpene production of chrysanthemum and the regulatory mechanisms involved remain unclear. Results We used gas chromatography‒mass spectrometry (GC‒MS) to identify 177 compounds, including 106 terpenes, in ten chrysanthemum cultivars. Monoterpene derivatives and sesquiterpenes were the most common. Next, we identified 27 candidate hub genes for terpene production in chrysanthemum via combined transcriptome and metabolome analysis, as well as weighted gene coexpression network analysis. The three terpenes synthesis-related genes were significantly expressed in the disc florets of the different chrysanthemum cultivars. We concluded that the transcription factors TCP8, TCP5, ATHB8, ATHB7, HAT22, TGA1, TGA4, and WHY1 may regulate terpene synthesis. Conclusions In this study, we profiled terpenes in chrysanthemum florets and constructed a key terpene-transcription factor network related to terpene synthesis. These findings lay the groundwork for future research into the mechanism of terpene synthesis in chrysanthemum as well as in other plants.

Basic helix–loop–helix (bHLH) transcription factor gene family in plants controls various growth and development aspects; however, the actual roles of these genes in flowering plants are not well known. In this study, a novel bHLH protein CmbHLH110 was found to interact with CmERF110 by in vitro and in vivo experiments, a chrysanthemum ERF110 homolog that acts as a positive flowering regulator. In addition, CmbHLH110 was also found to regulate the flowering of chrysanthemums, overexpression of CmbHLH110 causes chrysanthemums to flower earlier, and suppressed CmbHLH110 leads to delayed flowering. Furthermore, the loss-of-function Arabidopsis mutant of its homologue PERICYCLE FACTOR TYPE-A 5 (PFA5) had a noticeable late flowering phenotype, and CmbHLH110 completely complemented the late flowering phenotype of the pfa5 mutant, whereas heterologous overexpression of CmbHLH110 in Arabidopsis Col-0 caused early flowering. Transcriptome sequencing revealed significant differential expression of flowering-related and circadian clock-related genes in transgenic chrysanthemum. Therefore, we concluded that CmbHLH110, as a novel flowering regulator, could interact with CmERF110 to regulate flowering in chrysanthemum.

Abstract Background The NAC transcription factor family, which is recognized as one of the largest plant-specific transcription factor families, comprises numerous members that are widely distributed among various higher plant species and play crucial regulatory roles in plant immunity. Results In this paper, we provided a detailed summary of the roles that NAC transcription factors play in plant immunity via plant hormone pathways and reactive oxygen species pathways. In addition, we conducted in-depth investigations into the interactions between NAC transcription factors and pathogen effectors to summarize the mechanism through which they regulate the expression of defense-related genes and ultimately affect plant disease resistance. Conclusions This paper presented a comprehensive overview of the crucial roles that NAC transcription factors play in regulating plant disease resistance through their involvement in diverse signaling pathways, acting as either positive or negative regulators, and thus provided references for further research on NAC transcription factors.

Abstract 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.

Abstract Background The growth and ornamental value of chrysanthemums are frequently hindered by aphid attacks. The ethylene-responsive factor (ERF) gene family is pivotal in responding to biotic stress, including insect stress. However, to date, little is known regarding the involvement of ERF transcription factors (TFs) in the response of chrysanthemum to aphids. Results In the present study, CmHRE2-like from chrysanthemum (Chrysanthemum morifolium), a transcription activator that localizes mainly to the nucleus, was cloned. Expression is induced by aphid infestation. Overexpression of CmHRE2-like in chrysanthemum mediated its susceptibility to aphids, whereas CmHRE2-like-SRDX dominant repressor transgenic plants enhanced the resistance of chrysanthemum to aphids, suggesting that CmHRE2-like contributes to the susceptibility of chrysanthemum to aphids. The flavonoids in CmHRE2-like-overexpression plants were decreased by 29% and 28% in two different lines, whereas they were increased by 42% and 29% in CmHRE2-like-SRDX dominant repressor transgenic plants. The expression of Chrysanthemum-chalcone-synthase gene(CmCHS), chalcone isomerase gene (CmCHI), and flavonoid 3′-hydroxylase gene(CmF3’H) was downregulated in CmHRE2-like overexpression plants and upregulated in CmHRE2-like-SRDX dominant repressor transgenic plants, suggesting that CmHRE2-like regulates the resistance of chrysanthemum to aphids partially through the regulation of flavonoid biosynthesis. Conclusion CmHRE2-like was a key gene regulating the vulnerability of chrysanthemum to aphids. This study offers fresh perspectives on the molecular mechanisms of chrysanthemum-aphid interactions and may bear practical significance for developing new strategies to manage aphid infestation in chrysanthemums.

Color fading caused by a decrease in anthocyanin accumulation during the post-flowering stage significantly affects postharvest quality of chrysanthemum. However, the underlying mechanism by which anthocyanin accumulation decreases during the post-flowering stage still unclear, which greatly restricts design of molecular breeding in chrysanthemum. Here, a chrysanthemum SG7 R2R3 MYB transcription factor (TF), CmMYB3-like, was identified to have a function in regulating anthocyanin biosynthesis during the post-flowering stage. Quantitative real time PCR (qRT-PCR) assays showed that the expression of CmMYB3-like was gradually downregulated when anthocyanin content increased during the flowering stage and was significantly upregulated during the post-flowering stage. Genetic transformation of chrysanthemum and dual-luciferase assays in N. benthamiana leaves showed that CmMYB3-like suppressed anthocyanin accumulation by inhibiting the transcription of CmCHS and CmANS directly and that of CmF3H indirectly. However, overexpression or suppression of CmMYB3-like did not affect the biosynthesis of flavones or flavonols. Genetic transformation of chrysanthemum revealed that the overexpression of CmMYB3-like inhibited anthocyanin accumulation, but its suppression prevented the decrease in anthocyanin accumulation during the post-flowering stage. Our results revealed a crucial role of CmMYB3-like in regulating the color of petals during the post-flowering stage and provided a target gene for molecular design breeding to improve the postharvest quality of chrysanthemum.

Species from the Artemisia genus frequently have high resistance to pests and pathogens due to their being rich in secondary metabolites. Therefore, identifying bioactive components from Artemisia plants is essential for developing botanical pesticides and selecting parents for breeding resistant varieties of cultivated Chrysanthemum morifolium. This study investigated the resistance of four Artemisia species to aphids (Macrosiphoniella sanborni) and the antimicrobial properties of their extracts. Choice and no-choice assays showed that the tested four species had strong repellent and antifeedant effects on aphids compared with chrysanthemum. The antimicrobial activity of ethyl acetate extracts from different tissues against four pathogenic fungi was tested by disc diffusion assay. Among them, the extracts from Artemisia maximowicziana showed the strongest antimicrobial effect. The inhibition rates of Alternaria alternata, Colletotrichum siamense, and Phoma sp. caused by leaf extracts from A. maximowicziana were 53.8%, 54.95%, and 61.46%, respectively. And the inhibition increased to 75.44%, 51.65%, and 79.51%, respectively, using the stem extracts. However, the root extracts of Artemisia spp. showed only up to 25% to Fusarium solani. GC-MS analysis showed that the volatiles of Artemisia spp. were mostly abundant in terpenoids, but the components and contents were remarkably different among species. Further analysis of Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA) showed the most contributed component among all potentially antimicrobial bioactive components was (−)-thujol. In this study, A. maximowicziana was identified as the material with potential value as a parent for crossbreeding, and its primary volatile compound (−)-thujol with potential resistant active is worth further investigation.

Chrysanthemum black spot disease caused by Alternaria alternate infestation is a widespread and extremely destructive foliar disease of chrysanthemums. We compared the resistance of 14 chrysanthemum relatives to chrysanthemum black spot disease, and identified the main indicators for the evaluation and screening of chrysanthemum disease resistance, which is of great significance in laying the foundation for a larger-scale screening of chrysanthemum relatives for disease resistance and the breeding of new disease-resistant cultivars. After artificial inoculation and identification, two disease-resistant germplasm resources, 11 moderately resistant materials, and one sensitive material were obtained. In both resistant and susceptible species, we found that the trichome density and leaf wax content of the resistant material were significantly higher than that of the sensitive material, while the stomata size was smaller than that of the sensitive material. In addition, we found that the leaf extract of the disease-resistant germplasm effectively inhibited the growth rate of A. alternate mycelium on the plate, and GC-MS components found that the leaves of resistant germplasm contained more volatile antifungal organic compounds, of which the abundant falcarinol and Germacrene D might play an important role in resistance to chrysanthemum black spot disease. In summary, epidermal trichome density, wax content and terpene substance content are three important reference indicators for disease resistance evaluation of related genera of chrysanthemum. The identified resistant germplasm can also be used as parents for future cross-breeding or as rootstocks.

Abstract Background Anthocyanin is a class of important secondary metabolites that determines colorful petals in chrysanthemum, a famous cut flower. ‘Arctic Queen’ is a white chrysanthemum cultivar that does not accumulate anthocyanin during the flowering stage. During the post-flowering stage, the petals of ‘Arctic Queen’ accumulate anthocyanin and turn red. However, the molecular mechanism underlying this flower color change remains unclear. Results In this study, by using transcriptome analysis, we identified CmNAC25 as a candidate gene promoting anthocyanin accumulation in the post-flowering stage of ‘Arctic Queen’. CmNAC25 is directly bound to the promoter of CmMYB6, a core member of the MBW protein complex that promotes anthocyanin biosynthesis in chrysanthemum, to activate its expression. CmNAC25 also directly activates the promoter of CmDFR, which encodes the key enzyme in anthocyanin biosynthesis. CmNAC25 was highly expressed during the post-flowering stage, while the expression level of CmMYB#7, a known R3 MYB transcription factor interfering with the formation of the CmMYB6–CmbHLH2 complex, significantly decreased. Genetic transformation of both chrysanthemum and Nicotiana tabacum verified that CmNAC25 was a positive regulator of anthocyanin biosynthesis. Another two cultivars that turned red during the post-flowering stages also demonstrated a similar mechanism. Conclusions Altogether, our data revealed that CmNAC25 positively regulates anthocyanin biosynthesis in chrysanthemum petals during the post-flowering stages by directly activating CmMYB6 and CmDFR. Our results thus revealed a crucial role of CmNAC25 in regulating flower color change during petal senescence and provided a target gene for molecular design breeding of flower color in chrysanthemum.

Abstract 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.

Abstract 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.

Precise nitrogen supply is crucial for ensuring the quality of cut chrysanthemums (Chrysanthemum morifolium Ramat.). The nitrogen nutrition index (NNI) serves as an important indicator for diagnosing crop nitrogen (N) nutrition. Hyperspectral remote sensing (HRS) technology has been widely used in monitoring crop N status due to its rapid, accurate, and non-destructive capabilities. However, its application in estimating the NNI of cut chrysanthemums has received limited attention. Therefore, this study aimed to use HRS to accurately determine the cut chrysanthemum NNI, thereby providing valuable guidance for managing N fertilization. During several key growth stages, a hyperspectral spectroradiometer was used to capture hyperspectral reflectance data (350–2500 nm) from three leaf layers. Subsequently, cut chrysanthemum canopies were sampled for aboveground biomass (AGB) and plant nitrogen concentration (PNC). The collected AGB and PNC data were then utilized to fit the critical N (Nc) dilution curve of cut chrysanthemums using a Bayesian hierarchical model, enabling the calculation of the NNI. Finally, spectral indices and partial least squares regression (PLSR) were used to establish the NNI estimation model for cut chrysanthemums. The results showed that the Nc dilution curve of the cut chrysanthemums was Nc = 5.401 × AGB−0.468. The first leaf layer (L1) proved to be optimal for estimating cut chrysanthemum NNI. Additionally, a newly proposed two-band spectral index, DVI-L1 (R1105, R700), demonstrated moderate predictive capabilities for the NNI of cut chrysanthemums (R2 = 0.5309, RMSE = 0.3210). Compared with the spectral index-based NNI estimation model, PLSR-L1 showed the best performance in estimating the cut chrysanthemum NNI (R2 = 0.8177, RMSE = 0.2000). Our results highlight the rapid NNI prediction potential of HRS and its significance in facilitating precise N management in cut chrysanthemums.

Abstract The quantitative control of FLOWERING LOCUS T (FT) activation is important for the floral transition in flowering plants. However, the flowering regulation mechanisms in the day-neutral, summer-flowering chrysanthemum plant remain unclear. In this study, the chrysanthemum BBX7 homolog CmBBX7 was isolated and its flowering function was identified. The expression of CmBBX7 showed a diurnal rhythm and CmBBX7 exhibited higher expression levels than CmBBX8. Overexpression of CmBBX7 in transgenic chrysanthemum accelerated flowering, whereas lines transfected with a chimeric repressor (pSRDX-CmBBX7) exhibited delayed flowering. Yeast single hybridization, luciferase, electrophoretic mobility shift, and chromatin immunoprecipitation assays showed that CmBBX7 directly targets CmFTL1. In addition, we found that CmBBX7 and CmBBX8 interact to positively regulate the expression of CmFTL1 through binding to its promoter. Collectively, these results highlight CmBBX7 as a key cooperator in the BBX8–FT module to control chrysanthemum flowering. Graphical Abstract

Abstract Chrysanthemum (Chrysanthemum morifolium Ramat.) is a globally important ornamental plant with great economic, cultural, and symbolic value. However, research on chrysanthemum is challenging due to its complex genetic background. Here, we report a near-complete assembly and annotation for C. morifolium comprising 27 pseudochromosomes (8.15 Gb; scaffold N50 of 303.69 Mb). Comparative and evolutionary analyses reveal a whole-genome triplication (WGT) event shared by Chrysanthemum species approximately 6 million years ago (Mya) and the possible lineage-specific polyploidization of C. morifolium approximately 3 Mya. Multilevel evidence suggests that C. morifolium is likely a segmental allopolyploid. Furthermore, a combination of genomics and transcriptomics approaches demonstrate the C. morifolium genome can be used to identify genes underlying key ornamental traits. Phylogenetic analysis of CmCCD4a traces the flower colour breeding history of cultivated chrysanthemum. Genomic resources generated from this study could help to accelerate chrysanthemum genetic improvement.

Mitogen-activated protein kinases (MAPKs, also known as MPKs) regulate diverse cellular and physiological functions, and dual-specificity MAPK phosphatases (MKPs) modulate MAPK signalling through MAPK dephosphorylation and inactivation. Due to lacking of overall understanding for the regulatory networks between Chrysanthemum morifolium MKPs (CmMKPs) and C. morifolium MAPKs (CmMPKs), we systematically studied the interactions between four groups of CmMPKs and eight identified CmMKPs in chrysanthemum and found that the interaction between the specific CmMKP and the specific CmMPK differed from those in other plants. Furthermore, the expression of CmMKP1 and CmMKP1-LIKE1 showed opposite trends during the development of chrysanthemum flower buds under salt treatment and Alternaria alternata inoculation, but these genes could interact with the same CmMPKs, providing insight into the subfunctionalization of paralogues. Amino acid variations (M87V, T277P and V6L) in dual-specificity protein phosphatases (DsPTP1)-LIKE1/2/3 changed the interactions of these proteins with the four CmMPK groups in chrysanthemum, providing evidence for the de/neofunctionalization of paralogues in polyploids, suggesting that we can identify the key functional sites of proteins by studying polyploid paralogues.

With the rapid development of biotechnology, gene editing has become more widely used as a powerful tool to regulate plant traits directionally and efficiently. Here, we summarize the recent research progress in ornamental plant gene editing, including flower type, flower color, vase life, marker genes and other traits. We also discuss the application potential of other crop gene editing methods in ornamental plants and explore the diversity and feasibility of gene editing techniques in plant breeding to promote the molecular breeding of ornamental plants.

Abstract Background Chrysanthemum seticuspe has emerged as a model plant species of cultivated chrysanthemums, especially for studies involving diploid and self-compatible pure lines (Gojo-0). Its genome was sequenced and assembled into chromosomes. However, the genome annotation of C. seticuspe still needs to be improved to elucidate the complex regulatory networks in this species. Results In addition to the 74,259 mRNAs annotated in the C. seticuspe genome, we identified 18,265 novel mRNAs, 51,425 novel lncRNAs, 501 novel miRNAs and 22,065 novel siRNAs. Two C-class genes and YABBY family genes were highly expressed in disc florets, while B-class genes were highly expressed in ray florets. A WGCNA was performed to identify the hub lncRNAs and mRNAs in ray floret- and disc floret-specific modules, and CDM19, BBX22, HTH, HSP70 and several lncRNAs were identified. ceRNA and lncNAT networks related to flower development were also constructed, and we found a latent functional lncNAT–mRNA combination, LXLOC_026470 and MIF2. Conclusions The annotations of mRNAs, lncRNAs and small RNAs in the C. seticuspe genome have been improved. The expression profiles of flower development-related genes, ceRNA networks and lncNAT networks were identified, laying a foundation for elucidating the regulatory mechanisms underlying disc floret and ray floret formation.

Abstract Flowering is an important process in higher plants and is regulated by a variety of factors, including light, temperature, and phytohormones. Flowering restriction has a considerable impact on the commodity value and production cost of many horticultural crops. In Arabidopsis, the FT/TFL1 gene family has been shown to integrate signals from various flowering pathways and to play a key role in the transition from flower production to seed development. Studies in several plant species of the FT/TFL1 gene family have revealed it harbors functional diversity in the regulation of flowering. Here, we review the functional evolution of the FT/TFL1 gene family in horticulture plants and its unique regulatory mechanisms; in addition, the FT/TFL1 family of genes as an important potential breeding target is explored.

Crown diameter is one of the crucial indicators for evaluating the adaptability, growth quality, and ornamental value of garden chrysanthemums. To accurately obtain crown diameter, this study employed an unmanned aerial vehicle (UAV) equipped with a RGB camera to capture orthorectified canopy images of 64 varieties of garden chrysanthemums at different growth stages. Three methods, namely RGB color space, hue-saturation-value (HSV) color space, and the mask region-based convolutional neural network (Mask R-CNN), were employed to estimate the crown diameter of garden chrysanthemums. The results revealed that the Mask R-CNN exhibited the best performance in crown diameter estimation (sample number = 2409, R2 = 0.9629, RMSE = 2.2949 cm). Following closely, the HSV color space-based model exhibited strong performance (sample number = 2409, R2 = 0.9465, RMSE = 3.4073 cm). Both of the first two methods were efficient in estimating crown diameter throughout the entire growth stage. In contrast, the RGB color space-based model exhibited slightly lower performance (sample number = 1065, R2 = 0.9011, RMSE = 3.3418 cm) and was only applicable during periods when the entire plant was predominantly green. These findings provide theoretical and technical support for utilizing UAV-based imagery to estimate the crown diameter of garden chrysanthemums.

Nitrogen (N), phosphorus (P), and potassium (K) are three macronutrients that are crucial in plant growth and development. Deficiency or excess of any or all directly decreases crop yield and quality. There is increasing awareness of the importance of rhizosphere microorganisms in plant growth, nutrient transportation, and nutrient uptake. Little is known about the influence of N, P, and K as nutrients for the optimal production of Chrysanthemum morifolium. In this study, a field experiment was performed to investigate the effects of N, P, and K on the growth, nutrient use efficiency, microbial diversity, and composition of C. morifolium. Significant relationships were evident between N application rates, C. morifolium nutrient use, and plant growth. The N distribution in plant locations decreased in the order of leaf > stem > root; the distributions were closely related to rates of N application. Total P fluctuated slightly during growth. No significant differences were found between total P in the roots, stems, and leaves of C. morifolium vegetative organs. Principle component analysis revealed that combinations of N, P, and K influenced soil nutrient properties through their indirect impact on operational taxonomic units, Shannon index, and abundance of predominant bacterial taxa. Treatment with N, P, and K (600, 120, and 80 mg·plant−1, respectively) significantly improved plant growth and quality and contributed to the bacterial richness and diversity more than other concentrations of N, P, and K. At the flowering time, the plant height, leaf fresh weight, root dry weight, stem and leaf dry weight were increased 10.6%, 19.0%, 40.4%, 27% and 34.0%, respectively, when compared to the CK. The optimal concentrations of N, P, and K had a positive indirect influence on the available soil nutrient content and efficiency of nutrient use by plants by increasing the abundance of Proteobacteria, decreasing the abundance of Actinobacteria, and enhancing the potential functions of nitrogen metabolism pathways. N, P, and K fertilization concentrations of 600, 120, and 80 mg·plant−1 were optimal for C. morifolium cultivation, which could change environmental niches and drive the evolution of the soil microbial community and diversity. Shifts in the composition of soil microbes and functional metabolism pathways, such as ABC transporters, nitrogen metabolism, porphyrin, and the metabolism of chlorophyll II, glyoxylate, and dicarboxylate, greatly affected soil nutrient cycling, with potential feedback on C. morifolium nutrient use efficiency and growth. These results provide new insights into the efficient cultivation and management of C. morifolium.

The transcription factor family RELATED to ABSCISIC ACID INSENSITIVE3 (ABI3)/VIVIPAROUS1(VP1) (RAV) is a plant-specific group of transcription factors that only contain a conserved B3 DNA binding domain or both their own B3 and APETALA2 (AP2) domains belonging to the B3 superfamily, which is vital for plant growth, development, and stress response. Although genome-wide characterization and analysis of the RAV family genes have been conducted in some species, they have not been systematically reported in chrysanthemums. Here, we found six RAV family genes in the diploid Chrysanthemum seticuspe genome. Based on domain similarity and homology comparison analyses, RAV genes in Chrysanthemum were categorized into two clades: Class-I and Class-II. Conserved motif analysis revealed that all CsRAV proteins contained the B3 repression domain. An analysis of cis-acting elements suggested that CsRAV family genes may play parts in light, hormonal, abiotic stress, growth, and developmental processes. Furthermore, quantitative RT-PCR analysis validated that all six CsRAV genes responded to ethylene treatment, whereas the genes in the Class-I clade responded most significantly to ethylene. In summary, the above results provided a conceptual basis for further investigation into the functions of CsRAV genes in C. seticuspe.

Leaf disc transformation is one of the traditional methods that are now widely used in chrysanthemum with highly economical and ornamental value in world flower production, but it depends on plant genotypes and is time consuming and complicated. In addition, the transformation success rate of this method is low, generally ranging from 0.1% to 6.25%. Therefore, a highly efficient transformation system is needed. In this study, we are the first to establish a high-efficient chrysanthemum Agrobacterium-mediated transformation system via vacuum infiltration. Chrysanthemum stem internode explants were used as research material and CmLEC1 was used as a reporter gene. After approximately 3 months of culture and selection, the positive transgenic plants were obtained. Additionally, the positive probability was about 42%. The transformation efficiency was up to 37.7%, and if the escapes were removed, it was 16%. Furthermore, stable expression of CmLEC1 in transgenic 'Yuhualuoying' was confirmed by qRT-PCR analysis. These results suggest that this genetic transformation system via vacuum infiltration of chrysanthemum stem internode is highly efficient and convenient, and much better than traditional leaf disc transformation, and it will play an important role in chrysanthemum transformation and functional genetics research.

The response of Chrysanthemum japonense and C. nankingense to drought stress induced by polyethylene glycol was characterized at the level of leaf water status, leaf surface morphology and cuticular wax (quantity and composition), the activity of antioxidant enzymes, the extent of membrane lipid peroxidation, the accumulation of proline, photosynthesis performance and abscisic acid (ABA) accumulation. The more tolerant species C. japonense maintained its water status more effectively than C. nankingense, probably because its leaves form more cuticular wax and are able to accumulate higher levels of ABA. Superoxide dismutase activity was higher in C. japonense than in C. nankingense, as was that of catalase and ascorbate peroxidase during the later part of the stress episode, but levels of peroxidase were not differentiated at the end of the stress period. Membrane damage, as measured by electrolyte leakage and malondialdehyde accumulation, was less severe in C. japonense, which was also able to generate higher levels of free proline after a 10 h exposure to stress. Thus the superior response of C. japonense also reflects a more adapted system of osmoprotection and antioxidation. As a result, photosynthesis was compromised less by drought stress in C. japonense than in C. nankingense. That provides a scientific basis for the development and application of drought tolerance resources of chrysanthemum.

Hybridization is an important evolutionary mechanism ubiquitous to plants. Previous studies have shown that hybrid polyploidization of cultivated chrysanthemum, ‘Zhongshanzigui’, and Leucanthemum paludosum exhibit spring-flowering traits. This study explores the function of the LpFTLs gene via the phenotype of A. thaliana after heterologous transformation of the LpFTLs gene, and analyzes the mechanism ofthe continuous flowering phenotype and heterosis of hybrid offspring. The results suggest that the flowering phenotype of hybrid offspring in spring may be related to the expression of the LpFTLs gene. Ectopic expression of Leucanthemum paludosumLpFTLs in Arabidopsis thaliana resulted in earlier flowering, indicating that the LpFTLs gene also affects the flowering time in L. paludosum. Compound expression of FTLs in C. morifolium × L. paludosum intergeneric hybridization directly leads to serious heterosis in the hybrid offspring. Moreover, continuous flowering appears to be accompanied by hybrid weakness under the balance of vegetative and reproductive growth. Therefore, in future studies on chrysanthemum breeding, a suitable balance point must be established to ensure the target flowering time under normal growth.

The advancement of plant phenomics by using optical imaging-based phenotyping techniques has markedly improved breeding and crop management. However, there remains a challenge in increasing the spatial resolution and accuracy due to their noncontact measurement mode. Wearable sensors, an emerging data collection tool, present a promising solution to address these challenges. By using a contact measurement mode, wearable sensors enable in-situ monitoring of plant phenotypes and their surrounding environments. Although a few pioneering works have been reported in monitoring plant growth and microclimate, the utilization of wearable sensors in plant phenotyping has yet reach its full potential. This review aims to systematically examine the progress of wearable sensors in monitoring plant phenotypes and the environment from an interdisciplinary perspective, including materials science, signal communication, manufacturing technology, and plant physiology. Additionally, this review discusses the challenges and future directions of wearable sensors in the field of plant phenotyping.

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.

Temperature is an important environmental factor affecting plant anthocyanin synthesis. High temperatures are associated with decreased anthocyanin pigmentation in chrysanthemum. To reveal the effects of high temperature on anthocyanin biosynthesis in chrysanthemum, ray florets of the heat-sensitive cultivar “Nannong Ziyunying” (ZYY) were subjected to RNA sequencing. A total of 18,286 unigenes were differentially expressed between the control and treatment groups. Functional annotation and enrichment analyses of these unigenes revealed that the heat shock response and flavonoid pathways were significantly enriched, suggesting that the expression of these genes in response to high temperature is associated with the fading of chrysanthemum flower color. In addition, genes related to anthocyanin synthesis and heat shock response were differentially expressed under high-temperature stress. Finally, to further investigate the molecular mechanism of discoloration under high-temperature stress and facilitate the use of marker-assisted breeding for developing novel heat-tolerant cultivars, these results were used to mine candidate genes by analyzing changes in their transcription levels in chrysanthemum.

Abstract 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.

Abstract Background Through vernalization, plants achieve flowering competence by sensing prolonged cold exposure (constant exposure approximately 2-5 °C). During this process, plants initiate defense responses to endure cold conditions. Here, we conducted transcriptome analysis of Arabidopsis plants subjected to prolonged cold exposure (6 weeks) to explore the physiological dynamics of vernalization and uncover the relationship between vernalization and cold stress. Results Time-lag initiation of the two pathways and weighted gene co-expression network analysis (WGCNA) revealed that vernalization is independent of cold acclimation. Moreover, WGCNA revealed three major networks involving ethylene and jasmonic acid response, cold acclimation, and chromatin modification in response to prolonged cold exposure. Finally, throughout vernalization, the cold stress response is regulated via an alternative splicing-mediated mechanism. Conclusion These findings illustrate a comprehensive picture of cold stress- and vernalization-mediated global changes in Arabidopsis.

The endophytic microbiomes significantly differed across tea chrysanthemum cultivars and organs (stems and leaves). The most abundant endophytic bacterial genera were Pseudomonas, Masillia, and Enterobacter in the leaves and Sphingomonas and Curtobacterium in the stems of the five cultivars. Meanwhile, the most abundant endophytic fungal genera in the leaves and stems of the five tea chrysanthemums were Alternaria, Cladosporium, and Sporobolomyces. Specifically, Rhodotorula was dominant in the leaves of ‘Jinsi huangjv’ and Paraphoma was dominant in the stems of ‘Jinsi huangjv’. In all cultivars, the diversity and richness of endophytic bacteria were higher in leaves than in stems (p < 0.05). The highest diversity and richness of endophytic bacteria were recorded in ‘Chujv’, followed by ‘Jinsi huangjv’, ‘Fubai jv’, ‘Nannong jinjv’, and ‘Hangbai jv’. Meanwhile, endophytic fungi were less pronounced. Twenty-seven and 15 cultivable endophytic bacteria and fungi were isolated, four isolated endophytic bacteria, namely, CJY1 (Bacillus oryzaecorticis), CY2 (Pseudomonas psychrotolerans), JSJ7, and JSJ17 (Enterobacter cloacae) showed higher indole acetic acid production ability. Further field studies indicated that inoculation of these four endophytic bacteria not only promoted plant growth and yield but also increased total flavonoids, chlorogenic acid, luteolin, and 3,5-dicoffeylquinic acid levels in the dry flowers of tea chrysanthemums.

Autopolyploids often exhibit plant characteristics different from their diploid ancestors and are frequently associated with altered genes expression controlling growth and development. TCP is a unique transcription factor family in plants that is closely related to plant growth and development. Based on transcriptome sequencing of Chrysanthemum nankingense, 23 full-length TCP genes were cloned. The expression of CnTCP9 was most variable in tetraploids, at least threefold greater than diploids. Due to the lack of a C. nankingense transgenic system, we overexpressed CnTCP9 in Arabidopsis thaliana (Col-0) and Chrysanthemum morifolium. Overexpression of CnTCP9 caused enlargement of leaves in A. thaliana and petals in C. morifolium, and the expression of genes downstream of the GA pathway in C. morifolium were increased. Our results suggest that autopolyploidization of C. nankingense led to differential expression of TCP family genes, thereby affecting plant characteristics by the GA pathway. This study improves the understanding of enlarged plant size after autopolyploidization.

S genes are the key genes that cause plant self-incompatibility, to find out the key S genes and understand molecular mechanism of self-incompatibility in chrysanthemum, the stigmas and anthers at different developmental stages of 'Q10-22-2'—a self-incompatible chrysanthemum cultivar, were used for RNA sequencing. After bioinformatics analysis, 13 candidate pistil S genes and five candidate pollen S genes were excavated. A potential pistil S gene was cloned and named as CmSRK1. Meanwhile, a potential pollen S gene was cloned and named as CmPCP1. qRT-PCR revealed that CmSRK1 was specifically expressed in mature stigmas, and CmPCP1 was specifically expressed in anthers 3 d before maturation. Subcellular localization showed that both CmSRK1 and CmPCP1 were located in the nucleus and the cell membrane. Transcriptional activation activity analysis indicated that both of the two proteins had no transcriptional activation activity. Yeast two hybrid assay showed that there was no interaction between CmSRK1 and CmPCP1. CmSRK1 was constructed on the expression vector containing stigma-specific promoter, and CmPCP1 was constructed on the expression vector containing pollen-specific promoter, they were then transformed into Arabidopsis thaliana. Artificial hybridization was performed with transgenic lines containing CmSRK1 as the female parents, and transgenic lines containing CmPCP1 as the male parents. The hybridization results showed that seed sets of two transgenic lines were 19.62% and 11.64%, respectively, while cross-pollinated seed sets of Col-0 was 84.43%. Therefore, it was speculated that CmSRK1 and CmPCP1 might be pistil and pollen S genes of chrysanthemum, respectively, and SI of chrysanthemum belonged to SSI.

Chrysanthemums possess no metabolic pathway to synthesize delphinidin because of the lack of endogenous F3'5'H gene encoding the key enzyme in its biosynthetic pathway; therefore, there are no blue or blue-purple chrysanthemums occurring naturally. Currently, the introduction of exogenous F3'5'H into chrysanthemums is an efficient method for breeding bluish chrysanthemums. In this study, we explored the effects of the introduction of mutant CmF3'H (generated via site-directed mutagenesis, T485S, CmF3'Hm) and exogenous Osteospermum hybrid F3'5'H (OhF3'5'H) genes combined with Clitoria ternatea A3'5'GT (CtA3'5'GT) on delphinidin synthesis in chrysanthemum. Among the F3'5'H transgenic lines, those overexpressing endogenous CmF3'Hm could not generate blue flower color, although red color was changed to light pink due to CtA3'5'GT function. Meanwhile, OhF3'5'H introduction promoted the accumulation of delphinidin and its derivatives in chrysanthemum, changing the flower color from red-purple to purple-violet. These results indicate the applicability of exogenous OhF3'5'H and CtA3'5'GT transformation for promoting delphinidin synthesis during the molecular breeding of violet/blue chrysanthemums.

Drought causes water shortage and consequent retardation of plants growth and development. Therefore, improving the drought tolerance of plants is necessary for expanding cultivation and resource promotion. Increasing evidence indicates that phospholipase is involved in the response of plants to drought stress. The objective of this study was to create new drought-tolerant chrysanthemum germplasm, which lays a foundation for the study of the molecular mechanism of phospholipase mediated stress response in chrysanthemum. CmPLDα has the closest relationship with sunflower HaPLDα, and belongs to the PLDα family. CmPLDα over-expressing plants showed a slight shrinking under 20% PEG6000 treatment. The survival rate increased significantly by 1.7−1.8 times that of the wild type. Relative water content (RWC) of CmPLDα over-expressing plants were nearly 10% higher than that of the wild type. Relative electrical conductivity and MDA content were significantly lower than those of the wild type. ABA content of the over-expression lines Z1, Z2 were 1.3 and 1.22 times that of wild type, but ABA content of antisense lines F1, F2 was approximately 0.83 and 0.81 of those of wild type. Most plants of antisense transgenic lines F1, F2 were wrinkled, with a wilting index of 5 and 6, and the survival rate was also lower than that of the wild type after recovery growth. RWC of antisense lines were lower than over-expression lines, relative electrical conductivity and MDA content were significantly higher than those of the wild type. In summary, CmPLDα could enhance tolerance of chrysanthemum to drought conditions.

Abstract Background Chilling stress is the major factor limiting plant productivity and quality in most regions of the world. In the present study, we aimed to evaluate the effects of putrescine (Put) and polyamine inhibitor d-arginine (d-arg) on the chilling tolerance of anthurium (Anthurium andraeanum). Results Anthurium seedlings were pretreated with five different concentrations of Put solution or d-arg solution. Subsequently, the seedlings were subjected to chilling stress at 6 °C for 3 days, followed by a recovery at 25 °C for 1 day. Relative permeability of the plasma membrane, as well as physiological and morphologic parameters was assessed during the experiments. Additionally, transcriptome sequencing and patterns of differential gene expression related to chilling response were analyzed by qRT-PCR in 1.0 mM Put-treated and untreated anthurium seedlings. Results indicated that the supplementation of exogenous Put decreased the extent of membrane lipid peroxidation and the accumulation of malondialdehyde (MDA), promoted the antioxidant activities and proline content and maintained the morphologic performances compared with the control group. This finding indicated that the application of exogenous Put could effectively decrease the injury and maintain the quality of anthurium under chilling conditions. In contrast, the treatment of d-arg exhibited the opposite effects, which confirmed the effects of Put. Conclusions This research provided a possible approach to enhance the chilling tolerance of anthurium and reduce the energy consumption used in anthurium production.

Background: APETALA3 (AP3) has significant roles in petal and stamen development in accordance with the classical ABC model. Results: The AP3 homolog, CDM19, from Chrysanthemum morifolium cv. Jinba was cloned and sequenced. Sequence and phylogenetic analyses revealed that CDM19 is of DEF/AP3 lineage possessing the characteristic MIKC-type II structure. Expression analysis showed that CDM19 was transcribed in petals and stamens of ray and disc florets with weak expression in the carpels. Ectopic expression of CDM19 in Arabidopsis wild-type background altered carpel development resulting in multi-carpel siliques. CDM19 could only partially rescue the Arabidopsis ap3‐–3 mutant. Conclusions: Our results suggest that CDM19 may partially be involved in petal and stamen development in addition to having novel function in carpel development.How to cite: Githeng’u SK, Ding L, Zhao K, et al. Ectopic expression of Chrysanthemum CDM19 in Arabidopsis reveals a novel function in carpel development. Electron J Biotechnol 2020;45. https://doi.org/10.1016/j.ejbt.2020.03.001.

White rust caused by Puccinia horiana is a destructive disease of chrysanthemum plants. To better understand the resistance mechanisms of composite species to this disease, the leaf cuticular traits, antioxidant and defensive enzymes activities of immune (Chrysanthemum makinoi var. wakasaense) and highly susceptible (Ajania shiwogiku var. kinokuniense) species were compared. Trichome density of two species was markedly different, negatively associated with plant resistance to P. horiana. Total wax load in C. makinoi var. wakasaense was two times more than that in A. shiwogiku var. kinokuniense. The wax composition in immune one was abundant in esters and primary alcohols. Superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), polyphenoloxidase (PPO, EC 1.14.18.1 or EC 1.10.3.2) and phenylalanine ammonia lyase (PAL, EC 4.3.1.5) activities were investigated. In C. makinoi var. wakasaense, the activity of SOD and POD increased rapidly after inoculation, which might be non-host induced reactive oxygen species (ROS) activated antioxidant enzymes, however SOD and POD remained a low and steady level in the highly susceptible one after inoculation. Quick increase in PPO activities after inoculation was observed in both species, however it remained higher in C. makinoi var. wakasaense at the late period of inoculation. PAL in C. makinoi var. wakasaense was induced after pathogen inoculation, but not in A. shiwogiku var. kinokuniense, suggesting that these two enzymes might contribute to the resistance to P. horiana.

Ethylene is a gaseous phytohormone that delays flowering in Chrysanthemum morifolium Ramat. To date, however, there have been no systematic studies on genes involved in the ethylene response of this species, and the mechanism underlying ethylene-delayed flowering remains unclear. Herein, we applied RNA sequencing to characterize the ethylene response by comparing the transcriptomes of chrysanthemum cultivar ‘Jinba’ with or without ethephon treatment. Six unique RNA-seq libraries were generated. The identified differentially expressed genes (DEGs) primarily involved ethylene, auxin, and abscisic acid signaling genes; circadian clock genes; genes encoding functional proteins associated with floral transition, such as homologs of AP1/FRUITFUL-like 1 (AFL1), TERMINAL FLOWER 1 (TFL1), and so on; and genes encoding transcription factors, specifically of the MYB and bHLH families. Furthermore, quantitative RT-PCR was used to verify the DEGs identified by RNA-seq. Heterologous CmAFL1 overexpression in Arabidopsis thaliana resulted in early flowering. Our findings present a landscape of transcriptomes and reveal the candidate genes involved in the ethylene-mediated regulation of flowering time in chrysanthemum, providing useful data for further studies.

As a molecular chaperone, HSP70 is widely involved in complex activities in plants. Under high temperature, drought, high salt, low temperature, heavy metals, and other stresses, HSP70 is rapidly synthesizes, stabilizes protein and biological macromolecular structures, and improves the stress resistance of plants. In this study, 83 ClHSP70 genes in Chrysanthemum lavandulifolium were identified based on the published Chrysanthemum lavandulifolium genome database. The genes were divided into six clusters based on a phylogenetic analysis, and the gene structures, conserved motifs, and functional domains were relatively conserved. Only two collinear genes were observed, and they formed a pair of duplicating genes. Multiple abiotic stress and phytohormone response elements were observed on the ClHSP70 promoter, such as temperature, drought, methyl jasmonate, abscisic acid, and other stress-related elements, and CpG islands were found on some ClHSP70 promoters, suggesting that they may be related to methylation modifications. Tissue expression analysis showed that the ClHSP70 genes were highly expressed in the roots. In addition, the gene expression changed significantly after 1 h of heat treatment and plays an important role in plant responses to temperature stress. The results of this study provide insights on the ClHSP70 gene family members and a theoretical basis for further research on functional analyses of the ClHSP70 gene family.

Nuclear factor Y (NF-Y) is a class of transcription factors (TFs) with various biological functions that exist in almost all eukaryotes. In plants, heterotrimers composed of different NF-Y subunits are numerous and have different functions that can participate in the regulation of plant growth at various stages. However, NF-Y genes have not been systematically analyzed in chrysanthemum, only involving several NF-Y members. In this study, forty-six NF-Y members were identified from the diploid species Chrysanthemum seticuspe, including eight NF-YA members, twenty-one NF-YB members, and seventeen NF-YC members. These NF-Y genes were analyzed for their physicochemical characteristics, multiple alignments, conserved motifs, gene structure, promoter elements, and chromosomal location. Phylogenetic analysis revealed that only two gene pairs in C. seticuspe underwent gene duplication events. The Ka/Ks ratios were both less than one, indicating that the two pairs underwent purifying selection. Promoter element analysis showed that multiple abiotic stress and hormone response elements were present in the CsNF-Y genes, suggesting that these genes play an important role in the response to stress, growth, and development in plants. Further validation of candidate genes in response to drought regulation using RT-qPCR demonstrated that CsNF-Y genes in C. seticuspe play an important role in drought regulation.

Heat stress limits the growth and development of chrysanthemum seedlings. Although melatonin (MT) has been linked to the heat stress response in plants, research on the underlying molecular mechanisms is scarce. In this study, the regulatory networks of MT on heat stress in chrysanthemum seedlings were explored. Physiological measurements suggested that MT not only reduced malondialdehyde accumulation, hydrogen peroxide content, and superoxide anion free radical generation rate, but also significantly promoted osmotic regulation substance synthesis (proline and soluble protein), antioxidant accumulation (GSH and AsA), and the antioxidant enzyme activities (SOD, POD, CAT, and APX) in chrysanthemum leaves under heat stress. Furthermore, MT increased the fresh weight, dry weight, chlorophyll content, photosynthesis rate, and gas exchange indexes. Further, RNA-seq results revealed 33,497 and 36,740 differentially expressed genes in the S/Con and SMT/ConMT comparisons, respectively. The differences in the comparisons revealed that MT regulated heat shock transcription factors (HSFs) and heat shock proteins (HSPs), and the genes involved in Ca2+ signal transduction (CNGCs and CAM/CMLs), starch and sucrose metabolism (EDGL, BGLU, SuS, and SPS), hormone (PP2Cs, AUX/IAAs, EBFs, and MYC2), chlorophyll metabolism (HEMA and PORA), flavonoid biosynthesis (CHS, DFR, and FNS), and carotenoid biosynthesis (DXPS, GGDP, and PSY). MT effectively improved chrysanthemum seedling heat-resistance. Our study, thus, provides novel evidence of a gene network regulated by MT under heat stress.

Lily was grown worldwide as a fresh cutting flower because of its colorful petals, but its anther contained a large number of pollen grains that cause serious pollen contamination, however, pollen abortion can effectively reduce the level of pollen pollution. Our analysis aims to use cytological observation to detect the critical stage when pollen abortion occurs and to provide comprehensive gene expression information at the transcriptional level. The result showed that pollen abortion in ‘Little Kiss’ began at the mononuclear stage and the callose that covers the microspores failed to degenerate when young pollens were released from the tetrads. In addition, compared with the normally developed one, the tapetum of ‘Little Kiss’ degraded in advance while the degradation of callose was delayed. Furthermore, 103 differentially expressed genes (DEGs) related to the advance degeneration of tapetum cells and callose were found in the expression levels, including 22 transcription factors (TFs). In particular, two β-glucanase genes (endo-1,3(4)-β-glucanase, exo-β-glucanase) responsible for callose degeneration were significantly down-regulated. These results suggested that pollen abortion may occur at mononuclear stage and that early degeneration of tapetum cells resulted in a significant down-regulation of β-glucanase genes. As a result, the callose to cover microspores impedes the formation of pollen walls, which may possibly lead to pollen abortion. Keywords: Lilium Asiatic hybrids, microspore development, tapetum, programmed cell death, callose, transcription factor

Abstract MYB transcription factors are widely involved in the development of and physiological processes in plants. Here, we isolated the chrysanthemum R2R3-MYB family transcription factor CmMYB15, a homologous gene of AtMYB15. It was demonstrated that CmMYB15 expression was induced by aphids and that CmMYB15 could bind to AC elements, which usually exist in the promoter of lignin biosynthesis genes. Overexpression of CmMYB15 in chrysanthemum enhanced the resistance of aphids. Additionally, the content of lignin and the expression of several lignin biosynthesis genes increased. In summary, the results indicate that CmMYB15 regulates lignin biosynthesis genes that enhance the resistance of chrysanthemum to aphids.

Chrysanthemummorifolium is one of the four major cut flowers in the world, with high ornamental and economic value. Flowering time is an important ornamental characteristic of chrysanthemum that affects its value in the market. In Arabidopsis, the FRUITFULL (FUL) gene plays a key role in inducing flowering. Here, we isolated an FUL clade MADS-box gene, CmFL3, from chrysanthemum inflorescence buds. CmFL3 localized in the cellular membrane and nucleus, and showed no transcriptional activity in yeast. The qRT-PCR assay showed that CmFL3 was strongly expressed in the leaves, receptacles, and disc floret petals. Furthermore, CmFL3 was mainly detected in the inflorescence meristem and bract primordia using in situ hybridization. Similar to Arabidopsis, overexpression of CmFL3 in chrysanthemum induced early flowering. Particularly, the expression level of CmAFT was downregulated, whereas that of CmFTL3 was upregulated in the leaves of transgenic chrysanthemum lines. Meanwhile, the overexpression of CmFL3 in Arabidopsis also led to earlier flowering. Furthermore, the expression of AtFT, AtAP1, AtLFY, and AtFUL was significantly increased in CmFL3 transgenic Arabidopsis. The present study verified the function of CmFL3 in regulating flowering time and further revealed that it could affect the expression of other flowering-related genes—CmAFT and CmFTL3. Therefore, the CmFL3 gene may be an important candidate for genetic breeding aimed at regulating flowering.

Transcription factors, also known as trans-acting factors, balance development and stress responses in plants. Branching plays an important role in plant morphogenesis and is closely related to plant biomass and crop yield. The apical meristem produced during plant embryonic development repeatedly produces the body of the plant, and the final aerial structure is regulated by the branching mode generated by axillary meristem (AM) activities. These branching patterns are regulated by two processes: AM formation and axillary bud growth. In recent years, transcription factors involved in regulating these processes have been identified. In addition, these transcription factors play an important role in various plant hormone pathways and photoresponses regulating plant branching. In this review, we start from the formation and growth of axillary meristems, including the regulation of hormones, light and other internal and external factors, and focus on the transcription factors involved in regulating plant branching and development to provide candidate genes for improving crop architecture through gene editing or directed breeding.

Garden chrysanthemums are a group of chrysanthemums (Chrysanthemum morifolium) that are mostly used in garden landscape collocations. Because most garden chrysanthemum varieties have low plants and poor space effects, they have certain limitations in garden landscape applications. In this study, we selected seven garden chrysanthemum varieties with excellent characteristics for artificial hybridization and intercross parentage to obtain new varieties with good traits we need. The phenotypic characteristics of the F1 offspring in terms of plant height, crown width, crown height ratio, number of main branches, branching intensity, plant form, inflorescence diameter, number of flowers per plant, number of ray florets, flower color, and days from planting period to coloring period were analyzed and systematically evaluated. Subsequently, a comprehensive evaluation system was established using the analytic hierarchy process (AHP) and k-means clustering method. We built a comprehensive analysis model, calculated the weighting of each evaluation factor, and multiplied the weight value by the score of the evaluation index standard of each factor to obtain the comprehensive score of each plant. All F1 plants were divided into four grades: excellent grade accounting for 13%, good grade accounting for 28%, medium grade accounting for 36%, and poor grade accounting for 23%. Then, we analyzed the differences of some quantitative traits between Group E (hybrids in excellent grade) and Group O (hybrids in good, medium, and poor grades). There were significant differences in plant height, crown height ratio, and the number of main branches but no significant difference in crown width. Combining with comprehensive score showed that Group E performed well overall. Finally, we selected five hybrid offspring with the highest overall scores in Group E as excellent variety materials of garden chrysanthemum for hedgerow. They were CH22, YQ73, HY08, CQ80, and HY07, respectively. We also found that plant height, lodging resistance, crown height ratio, plant form, crown width, and the number of main branches could be the main indicators in the AHP, which can be effectively applied to the comprehensive evaluation and breeding of garden chrysanthemums for hedgerows.

Heat shock proteins (HSPs) play important roles in various stress conditions. In this study, CmHSP90.5, whose expression is induced by heat and salt, was cloned from a chrysanthemum (Chrysanthemum morifolium) ‘Jinba’ and expressed in Arabidopsis. We found that CmHSP90.5 localized in the chloroplast. The heterologous expression of CmHSP90.5 weakened the heat tolerance of Arabidopsis and reduced the activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), indicating that CmHSP90.5-mediated heat stress sensitivity may be partially due to the regulation of active oxygen cleavage. The levels of expression of AtHSP101, AtHSP15.7, and AtHSP17.6C in CmHSP90.5-overexpressing plants decreased compared with those in wild-type (WT) plants under heat stress, indicating that these HSPs and CmHSP90.5 coregulate a plant’s heat stress tolerance. In addition, the salt stress tolerance of the CmHSP90.5-overexpressing Arabidopsis decreased compared with that of WT plants; CmHSP90.5-overexpressing plants showed increased Na+ levels and decreased K+ and proline levels compared with those of WT plants. Interestingly, the expression of stress-related genes, such as the Na+/H+ antiporter encoding gene SOS1, high-affinity K+ transporter encoding gene HKT1;1, and proline synthesis gene AtP5CS1, decreased in CmHSP90.5-overexpressing plants under salt stress compared with those expressions in WT plants. Our findings lay a foundation for understanding the roles of CmHSP90.5 in response to abiotic stresses in chrysanthemum.

Abstract Sustained monoculture often leads to the inhibition of plant growth, the decrease of the soil microbial diversity, and changes in soil microbial community composition, particularly to the accumulation of soil‐borne pathogens. In this study, we conducted field experiments to investigate the practical effects of tilling the soil down to a depth of 40 cm (40dp) in combination with dazomet (D) soil fumigation and/or the application of a bio‐organic fertilizer (B) on chrysanthemum growth, with a focus on the potential mechanisms underlying the responses of the soil microbiome. The growth indices of chrysanthemum were significantly (p

Crop genetics: chrysanthemums that cope with water Researchers in China have identified several genes that help chrysanthemum plants withstand waterlogging. Fadi Chen’s team at Nanjing Agricultural University used high-throughput sequencing to search for correlations between genetic mutations and waterlogging tolerance in 88 chrysanthemum varieties. One analysis method identified 137 mutations linked to waterlogging tolerance, while a second uncovered 14 mutations. Comparing the two lists revealed 11 mutations common to both. Six of these mutations could improve waterlogging response by 25%, and the team found that the mutations could be combined to improve performance even further. The team developed and tested a genetic marker to identify one of the high-tolerance mutations, demonstrating how this information may help breeders. They also identified four genes linked with the 137 mutations. Altogether, these findings point the way towards breeding chrysanthemums with greater waterlogging tolerance.

The architecture of spray cut chrysanthemum is crucial for the quality and quantity of cut flower production. However, the mechanism underlying plant architecture still needs to be clarified. In this study, we measured nine architecture-related traits of 195 spray cut chrysanthemum varieties during a two-year period. The results showed that the number of upper primary branches, number of lateral flower buds and primary branch length widely varied. Additionally, plant height had a significant positive correlation with number of leaf nodes and total number of lateral buds. Number of upper primary branches had a significant negative correlation with primary branch diameter, primary branch angle and primary branch length. Plant height, total number of lateral buds, number of upper primary branches, stem diameter, primary branch diameter and primary branch length were vulnerable to environmental impacts. All varieties could be divided into five categories according to cluster analysis, and the typical plant architecture of the varieties was summarized. Finally, a genome-wide association study (GWAS) was performed to find potential functional genes.