Search

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 FROM AUTHOR]

Key message: The dynamic genetic architecture of flowering time in chrysanthemum was elucidated by GWAS. Thirty-six known genes and 14 candidate genes were identified around the stable QTNs and QEIs, among which ERF-1 was highlighted. Flowering time (FT) adaptation is one of the major breeding goals in chrysanthemum, a multipurpose ornamental plant. In order to reveal the dynamic genetic architecture of FT in chrysanthemum, phenotype investigation of ten FT-related traits was conducted on 169 entries in 2 environments. The broad-sense heritability of five non-conditional FT traits, i.e., budding (FBD), visible coloring (VC), early opening (EO), full-bloom (OF) and decay period (DP), ranged from 56.93 to 84.26%, which were higher than that of the five derived conditional FT traits (38.51–75.13%). The phenotypic variation coefficients of OF_EO and DP_OF were relatively large ranging from 30.59 to 36.17%. Based on 375,865 SNPs, the compressed variance component mixed linear model 3VmrMLM was applied for a multi-locus genome-wide association study (GWAS). As a result, 313 quantitative trait nucleotides (QTNs) were identified for the non-conditional FT traits in single-environment analysis, while 119 QTNs and 67 QTN-by-environment interactions (QEIs) were identified in multi-environment analysis. As for the conditional traits, 343 QTNs were detected in single-environment analysis, and 119 QTNs and 83 QEIs were identified in multi- environment analysis. Among the genes around stable QTNs and QEIs, 36 were orthologs of known FT genes in Arabidopsis and other plants; 14 candidates were mined by combining the transcriptomics data and functional annotation, including ERF-1, ACA10, and FOP1. Furthermore, the haplotype analysis of ERF-1 revealed six elite accessions with extreme FBD. Our findings contribute to the understanding of dynamic genetic architecture of FT and provide valuable resources for future chrysanthemum molecular breeding programs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. Chrysanthemum is an important ornamental species with great economic value. Here, the authors assemble the haploid genome of C. morifolium, reveal its segmental allopolyploid genomic composition (AA'B), and identify candidate genes associated with flower development, petal shape, and flower colour. [ABSTRACT FROM AUTHOR]

Waterlogging stress is one of the major abiotic stresses that negatively affect chrysanthemum (Chrysanthemum morifolium Ramat.) growth and development, thus reducing its productivity. Therefore, there is a need to develop waterlogging-tolerant chrysanthemum germplasms to deal with this problem, and the identification of tolerant wild chrysanthemum (C. indicum) is relevant to the improvement of cultivated chrysanthemum targeting resistance traits. In the current study, we aimed to evaluate the waterlogging tolerance of wild chrysanthemums by using the membership function value of waterlogging (MFVW) and multiple regression analysis based on seven morphological traits related to waterlogging tolerance. By MFVW, the investigated 19 C. indicum accessions were classified into five grades: one waterlogging-tolerant accession, 12 moderately waterlogging-tolerant accessions, and every two accessions for highly waterlogging-tolerant, waterlogging-sensitive, and highly waterlogging-sensitive types, respectively. Of all traits tested, Score, shoot fresh weight, and root fresh weight are considered reliable indicators, exhibiting a higher correlation with waterlogging tolerance. The mathematical evaluation model of waterlogging tolerance based on MFVW proved robust by comparing the observed MFVW and predicted Y values in two interspecific segregating F1 populations derived from C. indicum and C. japonense, with average R2 ranging between 0.957 and 0.982. The method established in the current study provides a reference for the rapid identification and accurate prediction of waterlogging tolerance in chrysanthemum germplasms, and the highly waterlogging-tolerant wild chrysanthemum germplasms identified herein help widen the genetic base for breeding chrysanthemum cultivars with desirable waterlogging tolerance. [ABSTRACT FROM AUTHOR]

The anemone type, featuring prominent and colored in tubular florets, is an attractive flower shape in chrysanthemums and, thus, desired by breeders and consumers. Understanding the genetic basis of anemone type flowers in chrysanthemum is crucial for breeding success. The current study conducted nine cross combinations from seven parents to investigate segregation patterns, parental effect, and the relationships between the heterosis of six tubular floral traits and parental genetic distance. Significant (P < 0.05) differences among the parents and crosses in various tubular floral traits and transgressive segregation was observed in both directions for most traits. The broad-sense heritability of the tubular floral traits varied from hB2 = 0.47 to 0.92 across different crosses. The considerable variation occurred for almost floral traits, thus indicating the substantial potential for selecting lines with the desirable traits. The segregation ratio of anemone to non-anemone followed 3:1 in anemone × anemone crosses and 1:3 in either non-anemone × anemone or anemone × non-anemone crosses, except for two reciprocal crosses derived from the parents 'Nannong Xuefeng' and 'QX096'. The F1 hybrids' performance was more inclined towards a vulnerable parent and involved less influence of maternal or paternal effects, displaying some extended declines and negative mid-parent heterosis (MPH). The phenotypic genetic distance was significantly negatively correlated with MPH for floral traits except for style length and disk flower diameter. In contrast, we observed no significant correlation between molecular marker-based genetic distance and MPH for all floral characteristics. The findings of the current work provide insights into the complex inheritance pattern of flower types and help achieve desirable improvement in anemone type chrysanthemums. [ABSTRACT FROM AUTHOR]

Chrysanthemum morifolium is a well‐known edible medicinal plant in Asia and some other regions. Content of selenium in Se‐enriched C. morifolium (SeCM) is significantly higher than that in traditional C. morifolium (non‐Se‐enriched C. morifolium, TCM). In order to understand health effects of SeCM, its chemical composition, lifespan‐prolonging activities, and impacts on antioxidant defense‐related gene expressions of model organism D. melanogaster were systematically studied. A total of eight phenols, including luteolin‐7‐O‐glucoside, linarin, luteolin, apigenin, diosmetin, acacetin, 3‐caffeoylquinic acid and 4,5‐dicaffeoylquinic acid, were identified in SeCM extract. Compared with TCM, SeCM exhibited superior antioxidant properties. Intake of SeCM dramatically reduced malondialdehyde level and increased activities of endogenous antioxidant enzymes in fruit flies. SeCM was able to upregulate gene expressions of Cu/Zn‐superoxide dismutase, Mn‐superoxide dismutase and hydrogen peroxide catalase, and extend lifespans of fruit flies. Comparatively high antioxidant capacities and lifespan‐prolonging activities of SeCM might be attributed to its abundant phenols and selenium, which probably ameliorated accumulation of free radicals and susceptibility to oxidative stress. These findings provide clues on further exploitation and utilization of Se‐enriched C. morifolium. Practical applications: Chrysanthemum morifolium has been used for nutraceutical and curative purposes in China for thousands of years. Se‐enriched C. morifolium typically contains more selenium than traditional C. morifolium, and is widely consumed in Asia and some other regions. Selenium is an essential micronutrient for humans, and selenium deficiency may result in several diseases such as myocardial infarction. SeCM is one of important selenium supplements. In this study, SeCM was found to upregulate gene expressions of Cu/Zn‐superoxide dismutase, Mn‐superoxide dismutase, and hydrogen peroxide catalase, and extend lifespans of experimental animals. These results provide supporting information for developing SeCM‐based functional foods with distinct health benefits. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary: 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. [ABSTRACT FROM AUTHOR]

An appreciation of the genetic diversity retained in the gene pool of anemone‐type chrysanthemums is needed to drive further genetic improvement of this commercially important ornamental species. Here, a panel of 67 accessions was characterized with respect to both floral morphology, assessed using a set of 12 inflorescence‐associated traits, and to genotype, using sequence‐related amplified polymorphism (SRAP) fingerprinting. Abundant variation and a high level of broad‐sense heritability (>88%) were revealed for all traits except number of tubular floret lobes. Of the possible 66 pairwise inter‐trait combinations, 37 proved to be significantly correlated. A principal component analysis of the trait data showed that the first four principal components explained ~78% of the variance; meanwhile a hierarchical clustering analysis revealed a number of discrete groups reflecting the various cultivated types, but was not predictive of provenance. The SRAP genotyping employed 22 primer combinations and generated 238 informative fragments. A moderately high level of the Jaccard's similarity coefficient (mean 0.67) was calculated for the examined panel. A hierarchical clustering analysis based on the genotypic data revealed four groups, which were clearly reflective of cultivated type; moreover, a comparison of the within‐cluster means for each of the two key anemone‐related traits—tubular floret length and tubular floret length/style length—showed that the genotype‐based clusterings were associated with the anemone levels, albeit imperfectively. A principal coordinate analysis showed that the first two coordinates accounted for about 14% of the total variation. In summary, the present study adds new understanding of the genetic diversity present in the anemone‐type chrysanthemum gene pool, and the findings will lay the foundation for implementing a genotype/phenotype association strategy to reveal the genetic and molecular basis of floral form in this valuable ornamental species. [ABSTRACT FROM AUTHOR]

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 hB2 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. [ABSTRACT FROM AUTHOR]

Main conclusion : Forty-five molecular markers were detected significantly associated with chrysanthemum' waterlogging tolerance, and four favorable parental lines were identified as potential donors for improving waterlogging tolerance in chrysanthemum. The productivity of chrysanthemum is downgraded by waterlogging soils, which has driven a search for germplasm showing an enhanced level of waterlogging tolerance (WT). As yet little is known regarding the mode of inheritance of WT in chrysanthemum. The study set out to characterize the extent of genetic variation for WT represented in a collection of one hundred chrysanthemum accessions by testing them under both greenhouse and field conditions. A membership function value of waterlogging (MFVW), which integrated a wilting index, a chlorosis score and the proportion of dead leaf in waterlogged plants, was used as a measure of WT. The variation for MFVW among plants grown in the greenhouse (two experiments) was generally higher than that generated in field-grown (one experiment) plants. The MFVW broad sense heritability was 0.82, and the phenotypic coefficient of variation (31.8 %) was larger than the genetic one (28.8 %). Association mapping (AM) identified 45 markers related to WT: 25 by applying the general linear model (GLM) + principal component (PC) model, 16 by applying the mixed linear model (MLM), 31 by applying the MLM + Q matrix model and 12 by applying the MLM + PC model. Of the associated markers, eight and two were predictive in two and three experiments within all models, respectively; the proportion of the phenotypic variance explained by the eight associations ranged from 6.3 to 16.4 %. On the basis of their harboring all four of the leading markers E2M16-2, SSR150-6, E19M16-1 and E10M10-12, the varieties 'Nannong Xuefeng', 'Qx097', 'Nannong Xunzhang' and 'Finch' were identified as potential donors for future improvement of WT in chrysanthemum. [ABSTRACT FROM AUTHOR]

The phylogenetic relationships among Chrysanthemum and its related genera (Anthemideae, Asteraceae) is poorly understood. In the present study, these relationships were investigated using 45S and 5S ribosomal DNA (rDNA)-targeted fluorescent in situ hybridization. The results showed that there were two 45S rDNA signals present in Crossostephium chinense , four 45S rDNA signals in Cercidiphyllum japonicum , Artemisia sieversiana , Artemisia annua and Artemisia absinthium , six 45S rDNA signals in Chrysanthemum boreale and Pyrethrum parthenium , eight 45S rDNA signals in Chrysanthemum nankingense , Chrysanthemum dichrum , Chrysanthemum lavandulifolium and Tanacetum vulgare , and ten 45S rDNA signals in Ajania przewalskii . For the 5S rDNA locus, two 5S rDNA signals were present in C . nankingense , C . dichrum , C . lavandulifolium , C . boreale , C . japonicum , C. chinense and P. parthenium , four in A. sieversiana , A . annua , A . absinthium and A. przewalskii , and six 5S in T. vulgare . In addition, karyotypes of the 12 species were investigated. From this study, we inferred that Chrysanthemum was closely related to Ajania , and that Chrysanthemum species originating from China and Japan may have evolved differently. These findings add a new level to the understanding of the phylogenetic relationships of Chrysanthemum and related genera. [ABSTRACT FROM AUTHOR]

Branching is an important horticultural trait that influences plant architecture and production of cut chrysanthemum; however, its genetic determinism is poorly understood. In this study, an F mapping population derived from a cross between two spray cut chrysanthemum cultivars was used to determine QTL underlying branching. The branching traits in the F mapping population exhibited over-parent segregation and relatively high heritability (0.68-0.92). Based on the branching traits across two consecutive years, 16 additive QTL, including five QTL for primary branch number, each four QTL for branch height, and branch angle, and three QTL for primary branch length, were identified, with each accounting for 6.9-24.4 % of the phenotypic variation. Of these, four QTL expressed stable, located in the same genomic regions across two consecutive years. Results from this study add new understanding of the genetic basis of branching in spray cut chrysanthemum, and the putative major QTL detected here are valuable for future breeding cut chrysanthemum that exhibits desirable branching type. [ABSTRACT FROM AUTHOR]

Plant architecture is important for chrysanthemum cultivation and breeding. To determine the genetic basis of plant architectural traits in chrysanthemum, a population of 142 F1 plants derived from a cross between the creeping ground-cover chrysanthemum cultivar Yuhualuoying and the erect potted cultivar Aoyunhanxiao was used to detect quantitative trait loci (QTL) associated with plant height, plant width, inter-node length and flower neck length. The broad-sense heritability h for the four plant architectural traits ranged from 0.33 to 0.83, and transgressive segregation was observed. Single-locus QTL analysis revealed a total of five QTL, accounting for 6.0-16.1% of the phenotypic variation. Additionally, 11 pairs of epistatic QTL were identified, explaining 3.5-14.5% of the phenotypic variations. The majority of the interactions detected occurred between background loci. These results indicate that both additive and epistatic effects contribute to phenotypic variation in the plant architecture of chrysanthemum. It is expected that the identified markers associated with the additive QTL and epistatic QTL detected in this study will be of importance in future breeding programs to develop chrysanthemum cultivars exhibiting desirable plant architecture. [ABSTRACT FROM AUTHOR]

The inheritance of two flowering traits of chrysanthemum, initial blooming time and the duration of flowering, was investigated using segregation within an F population derived from a cross between the autumn-flowering 'Yuhualuoying' and the summer-flowering 'Aoyunhanxiao' cultivars. The analysis, based on a single segregating generation and the major gene plus polygene mixed inheritance model, showed that the inheritance of both traits was compatible with the presence of two pairs of major genes displaying additivity-dominance-epistasis, with additivity predominating. As the heritability of both pairs of major genes was high (initial blooming time ~65%, duration of flowering ~72%), it should be possible to select for both traits in early breeding generations. A marker-trait association analysis based on sequence-related amplified polymorphism (SRAP) genotyping uncovered 10 (initial blooming time) and 12 (duration of flowering) markers significantly associated with phenotype, cumulatively explaining, respectively, 46 and 54% of the variation. Some potentially useful markers were identified. [ABSTRACT FROM AUTHOR]

Chrysanthemum ( Dendranthema morifolium) is an economically important ornamental species and comprises a large proportion of the flower industry in south-east Asian and European countries. In this study, a segregating population of 142 F progeny of the cross between the two chrysanthemum cultivars 'Yuhualuoying' and 'Aoyunhanxiao' was used to construct two separate genetic linkage maps via a double pseudo-testcross mapping strategy. Genotyping was performed using 500 SRAP primer combinations, of which about 50% were informative. This allowed the definition of 896 SRAP loci, of which about 23% showed some segregation distortion. The 'Yuhualuoying' map consisted of 333 testcross markers arranged into 57 linkage groups (LGs). It covered >1,900 cM with a mean inter-marker distance of 6.9 cM. The map constructed from 'Aoyunhanxiao' comprised 342 test cross markers arranged into 55 LGs. It spanned nearly 1,900 cM, with a mean inter-marker distance of 6.6 cM. The markers were distributed rather uniformly along both maps. A quantitative trait loci analysis was conducted to investigate the pattern of inheritance of three inflorescence traits. This led to the detection of 12 putative loci at a LOD score >2.5, of which four each specified flower diameter, ray floret layer number, and ray floret length. This study provides molecular mapping information on marker-assisted selection programs for the improvement of multiple traits of interest. [ABSTRACT FROM AUTHOR]

Abstract: A genetic linkage map of chrysanthemum (Chrysanthemum morifolium) was constructed by genotyping 142 F1 progeny of the bi-parental cross ‘Yuhualuoying’בAoyunhanxiao’ with a combination of RAPD, ISSR and AFLP markers in a double pseudo-testcross mapping strategy. A total of 567 polymorphic markers, including 153 RAPDs, 61 ISSRs and 353 AFLPs, were used in linkage mapping. 336 of 567 (60%) markers were grouped on the two parental maps, leaving 231 (40%) markers unlinked. In the ‘Yuhualuoying’ linkage map, 210 markers including 116 testcross and 94 intercross markers were placed in 12 major and 32 minor (8 triplets and 24 doublets) linkage groups, covering 1034cM with an average map distance of 6.2cM between adjacent markers. In ‘Aoyunhanxiao’ linkage map, 190 markers consisting of 113 testcross and 77 intercross markers were resolved into 9 major and 24 minor linkage groups, with genome coverage of 1095cM and a mean inter-marker separation of 6.9cM between adjacent markers. Six pairs of homologous linkage groups were established on the basis of 64 intercross markers shared by the two parental maps. The maps lay a foundation for further quantitative traits loci (QTL) mapping and marker-assisted breeding of chrysanthemum. [Copyright &y& Elsevier]

Chrysanthemums are sensitive to waterlogging stress, and the development of screening methods for tolerant germplasms or genes and the breeding of tolerant new varieties are of great importance in chrysanthemum breeding. To understand the genetic basis of waterlogging tolerance (WT) in chrysanthemums, we performed a genome-wide association study (GWAS) using 92,811 single nucleotide polymorphisms (SNPs) in a panel of 88 chrysanthemum accessions, including 64 spray cut and 24 disbud chrysanthemums. The results showed that the average MFVW (membership function value of waterlogging) of the disbud type (0.65) was significantly higher than that of the spray type (0.55) at P < 0.05, and the MFVW of the Asian accessions (0.65) was significantly higher than that of the European accessions (0.48) at P < 0.01. The GWAS performed using the general linear model (GLM) and mixed linear model (MLM) identified 137 and 14 SNP loci related to WT, respectively, and 11 associations were commonly predicted. By calculating the phenotypic effect values for 11 common SNP loci, six highly favorable SNP alleles that explained 12.85—21.85% of the phenotypic variations were identified. Furthermore, the dosage-pyramiding effects of the favorable alleles and the significant linear correlations between the numbers of highly favorable alleles and phenotypic values were identified (r2 = 0.45; P < 0.01). A major SNP locus (Marker6619-75) was converted into a derived cleaved amplified polymorphic sequence (dCAPS) marker that cosegregated with WT with an average efficiency of 78.9%. Finally, four putative candidate genes in the WT were identified via quantitative real-time PCR (qRT-PCR). The results presented in this study provide insights for further research on WT mechanisms and the application of molecular marker-assisted selection (MAS) in chrysanthemum WT breeding programs. 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. [ABSTRACT FROM AUTHOR]

Chrysanthemum (Chrysanthemum morifolium Ramat.) is a leading flower with applied value worldwide. Developing new chrysanthemum cultivars with novel characteristics such as new flower colors and shapes, plant architectures, flowering times, postharvest quality, and biotic and abiotic stress tolerance in a time- and cost-efficient manner is the ultimate goal for breeders. Various breeding strategies have been employed to improve the aforementioned traits, ranging from conventional techniques, including crossbreeding and mutation breeding, to a series of molecular breeding methods, including transgenic technology, genome editing, and marker-assisted selection (MAS). In addition, the recent extensive advances in high-throughput technologies, especially genomics, transcriptomics, proteomics, metabolomics, and microbiomics, which are collectively referred to as omics platforms, have led to the collection of substantial amounts of data. Integration of these omics data with phenotypic information will enable the identification of genes/pathways responsible for important traits. Several attempts have been made to use emerging molecular and omics methods with the aim of accelerating the breeding of chrysanthemum. However, applying the findings of such studies to practical chrysanthemum breeding remains a considerable challenge, primarily due to the high heterozygosity and polyploidy of the species. This review summarizes the recent achievements in conventional and modern molecular breeding methods and emerging omics technologies and discusses their future applications for improving the agronomic and horticultural characteristics of chrysanthemum. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The anemone-type inflorescence of chrysanthemum features prominent, colored tubular florets. Here, the inheritance of a set of traits associated with floral form was investigated using a quantitative trait locus (QTL) mapping approach applied to a segregating population bred from a cross between the two varieties 'Nannong Xuefeng' and 'Monalisa'. The coefficient of variation of the various traits ranged from 12.8 to 59.2%, with an average of 28.0%, and there was notable transgressive segregation in both directions. A set of 26 QTL was uncovered, explaining a portion of the variation in eight of the eleven traits; individually, the loci accounted for between 6.3 and 11.9% of the phenotypic variation. A further 16 pairs of epistatically acting QTL were identified, associated with a contribution of between 3.7 and 13.6% of the phenotypic variance; the majority of these interactions involved background loci. The conclusion was that both additive and epistatic effects were involved in the genetic determination of floral form in chrysanthemum. [ABSTRACT FROM AUTHOR]

Low temperature is a major stress factor that has adverse effects on chrysanthemum production; however, there is little information regarding the genetic mechanism of cold tolerance. Based on a previously constructed F1 mapping population, genetic variations and QTL effects were investigated for cold tolerance at the vegetative, bud, flower, and rhizome stages. The results showed that the coefficient of variation for cold tolerance at the four growth stages ranged from 22.17 to 46.14%, and heterosis and transgressive segregation were observed in both directions. Mixed inheritance model analysis revealed that cold tolerance at the vegetative and flower stages was controlled by two pairs of major genes that exhibited additivity-dominance-epistasis effects, and the heritabilities of the major genes were 88.56% and 65.86%, whereas no major gene model was identified for cold tolerance at the bud and rhizome stages. A total of 15 cold-tolerance-associated QTLs that explained 6.47–68.89% of the phenotypic variation were detected across the four stages, four of which were synergistic QTLs. Most of the identified QTLs were expressed at 2–4 growth stages, but only one QTL was identified at all four stages. This finding indicated that the QTLs underlying cold tolerance were dependent on the environment and were selectively expressed at different stages. In addition, for cold tolerance at the bud and flower stages, the QTLs qBdsCTM33 and qFfsCTM33 on the M33 linkage group accounted for 65.78% and 68.89% of the phenotypic variation, respectively, but had corresponding negative additive effects of − 5.16 and − 4.57 °C, indicating that these QTLs are major contributors to the improvement of cold tolerance. The findings of the present study reveal the genetic architecture of cold tolerance at different developmental stages, and the major QTLs and linked molecular markers identified represent an important step toward molecular-marker-assisted selection and QTL pyramiding for future breeding of cold-tolerant chrysanthemum. [ABSTRACT FROM AUTHOR]

The original article unfortunately contains an incorrect article type. [ABSTRACT FROM AUTHOR]

An anemone shape featuring elongated and pigmented disk florets is an important target in breeding for flower shape in chrysanthemum. A good understanding of the inheritance of anemone-related traits and specific molecular markers are vital for accelerating the breeding progress. In this study, two segregating intercultivar F1 populations of the anemone-type 'Nannong Xuefeng' × the nonanemone-type 'QX096' (80 lines) and the same anemone-type 'Nannong Xuefeng' × 'Monalisa' (144 lines) were employed to investigate the genetic variation of anemone traits, and the anemone-specific markers were developed via the bulked segregant analysis (BSA) method by constructing two extreme bulks from each 10 anemone-type and nonanemone-type F1 lines, respectively. A moderate high level of variation coefficient (~ 24 to 57%) was obtained for most tubular floret traits relevant to the anemone type in both segregating populations. The anemone morphology of the hybrids was intermediate between that of their parents, and some transgressive individuals were observed, indicating great potential for the selection of lines with the desirable anemone type. In the BSA, four sequence-related amplified polymorphism (SRAP) primer combinations were identified as informative between the bulks of the anemone and nonanemone F1 individuals. After cloning and sequencing, only one SRAP marker, i.e., M11E1_272, was successfully converted to the sequence-characterized amplified region (SCAR) marker SCAR168. The SCAR marker was validation in the two F1 populations demonstrated that the marker SCAR168 could truly discriminate anemone and nonanemone types with a high coincidence ratio 87.86~92.5%. In addition, a general linear model (GLM)-based association analysis (P < 0.01) revealed that the SCAR marker exhibited a positive effect on the anemone traits and explained 20.83~33.66% phenotypic variation. Results of the current study show the inheritance pattern of anemone traits, and the developed anemone-specific SCAR marker paves the way for the marker-assisted selection of flower shape in chrysanthemum. [ABSTRACT FROM AUTHOR]

The establishment of a (set of) stably expressed reference gene(s) is required to normalize transcription data. Polyploidy is very common in the plant kingdom, but it is not necessarily the case that a reference gene which works well at the diploid level will also work well at the polyploid level. Here, ten candidate reference genes are compared in the context of gene transcription in the genus Chrysanthemum. The robustness of some, but not all, of these was shown to be high across ploidy levels. MTP (metalloprotease) and ACTIN (actin) were the most stable in diploid and tetraploid C. nankingense, while PSAA (photosynthesis-related plastid gene representing photosystem I) and EF-1α (elongation factor-1α) were the most stable in tetraploid and hexaploid C. zawadskii. EF-1α and PGK (phosphoglycerate kinase) was the best combination for the complete set of four taxa. These results suggest that when making cross-species comparison of transcript abundance involving different ploidy levels, care needs to be taken in the selection of reference gene(s). [ABSTRACT FROM AUTHOR]

• Bulked segregant analysis coupled with whole-genome sequencing (BSA-seq) was used to excavate major loci and genes for anemone type flower in chrysanthemum. • Three out of twenty-two key candidate genes were screened out by a combination of gene functional annotation, transcriptome and qRT-PCR analyses. • The developed KASP markers would help in marker-assisted selection of anemone type flower in chrysanthemum molecular breeding. Chrysanthemum is one of the most leading commercial flower crops well-known for its flower shape diversity. Anemone type chrysanthemums receive increasing market attention that are distinguished by their pigmented and elongated disk florets. However, there are few reports on quantitative trait loci (QTL) mapping and the identification genes for anemone in chrysanthemum. In this study, bulked segregant analysis coupled with whole-genome sequencing (BSA-seq) approach was employed to detect candidate genomic regions controlling anemone type flower. Two mixed DNA pools composed of 28 anemone type and 20 non-anemone type F 1 lines derived from a cross between 'Nannong Xuefeng' and 'Monalisa' together with two parents were used for high-throughput sequencing. A total of 42 consistent QTLs covering 30.00 Mb were simultaneously identified by |△(SNP/InDel-index)| and Euclidean distance (ED) algorithms based on 15,783,313 SNPs (single-nucleotide polymorphisms) and 1,546,200 small InDels (insertions and deletions). Twenty-two key candidate genes were screened out by a combination of gene functional annotation and transcriptome analysis, in which evm.model.scaffold_915.436 (CBF5), evm.model.scaffold_24.208 (U2AF65A), and a uncharacterized gene evm.model.scaffold_260.201 were highlighted by qRT-PCR. Furtherly, four associations were successfully converted to KASP (kompetitive allele specific PCR) markers, among them, the KASP markers developed for SNP locus Chr6__33961007 and Chr6__179207697 were proven to efficiently discriminate anemone and non-anemone type chrysanthemums being a couple of diagnostic markers in two populations. The results presented herein provide insights for further research on elucidating the formation mechanism of anemone type flower, and the anemone-specific KASP marker will be highly useful for applying MAS to accelerate breeding improvement of chrysanthemum. [ABSTRACT FROM AUTHOR]

High-density genetic maps are a valuable tool for quantitative trait locus (QTL) mapping and gene discovery for important traits in plants. However, such work in chrysanthemum remains largely unexplored, primarily owing to its large genome and complex genetic background. In this study, a high-density map containing 11,941 SNP bins spanning a total of 2967.76 cM in 27 linkage groups (LGs) with an average intermarker distance of 0.26 cM was developed with a genotyping by sequencing (GBS) approach. A total of 34 QTL clusters for waterlogging tolerance (WAT) were detected via multiple-QTL mapping (MQM) algorithms. A total of 186 candidate genes within these QTL clusters were mined in combination with transcriptome data. One key candidate gene within the QTL cluster cWAT6.1 , which belongs to group VII ethylene response factors (CmWAT6.1), was proven to be a positive regulator of WAT in chrysanthemum. Furthermore, transcriptomic assays of transgenic and wild-type chrysanthemums under normal conditions as well as further experiments provided evidence that CmWAT6.1 regulated WAT by promoting cell wall formation and lignin biosynthesis and coordinating oligosaccharide metabolic processes. This study represents important progress in gene mining through forward genetics, provides valuable genetic resources for further WAT improvement and provides new insight into the molecular mechanism of WAT in chrysanthemum. • A high-density map with an average intermarker distance of 0.26 cM for 27 linkage groups was constructed. • A total of 34 stable QTL clusters for waterlogging tolerance were detected via QTL mapping • 186 candidate genes within QTL clusters were mined in combination with gene functional annotation and transcriptome data. • CmWAT6.1 was proven to be a positive regulator of chrysanthemum waterlogging tolerance by promoting lignin biosynthesis. [ABSTRACT FROM AUTHOR]

• Extensive and continuous variations for leaf angle related traits were observed among 200 cut chrysanthemum accessions across two years. • 100 stable quantitative trait nucleotides (QTNs) and 75 QTN×environments interactions (QEIs) were identified to be associated with leaf angle using multi-locus genome-wide association study via 3VmrMLM. • 26 known and 32 novel genes mined here will contribute to the molecular breeding program of chrysanthemum plant architecture. • Haplotype analysis of ARF16 revealed four accessions with elite leaf angle as potential donors for improving chrysanthemum leaf angle. Chrysanthemum (Chrysanthemum morifolium Ramat.), one of the four most popular cut flowers in the world, occupies a large share of global floriculture trade. Leaf angle (LA) is an important factor affecting plant architecture, photosynthesis and yields of cut chrysanthemum. However, the genetic basis and related genes underlying LA remain largely unknown. In this research, phenotypes of five LA-related traits in 200 cut chrysanthemum accessions were investigated across two consecutive years (Y2020 and Y2021), and their broad-sense genetic heritabilities ranged from 68.91% to 84.70%. Leaf orientation value (LOV) exhibited the maximum phenotypic coefficient of variation of 35.66% in Y2020 and 32.34% in Y2021. A new methodological framework named 3VmrMLM was applied for multi-locus genome-wide association study (GWAS) based on a set of 330,710 single nucleotide polymorphisms (SNPs) to explore the genetic loci and candidate genes of LA. As a result, 303 quantitative trait nucleotides (QTNs) in single-environment, 120 QTNs and 75 QTN × environments interactions (QEIs) in multiple-environments were identified. Among the genes around these QTNs and QEIs, 26 known genes were considered to be associated with LA, including ARF16, IBH1, AN3 , etc. Furthermore, the haplotype analysis of ARF16 revealed four accessions with elite LA. Our findings provide a fundamental understanding to the genetic architecture of LA and contribute to further gene cloning and molecular improvement of chrysanthemum plant architecture. [ABSTRACT FROM AUTHOR]

TOPLESS (TPL)/TOPLESS-related (TPR) corepressors are important regulators of plant growth and development, but their functions in chrysanthemum (Chrysanthemum morifolium) are currently unclear. In this study, a chrysanthemum TPL/TPR family gene, designated CmTPL1-1 , was characterized. This gene encodes an 1135-amino-acid polypeptide harboring a conserved N-terminal domain and two C-terminal WD40 domains. CmTPL1-1 showed no transcriptional activity in yeast, and a localization experiment indicated that it localized to the nuclei in onion epidermal cells. Transcript profiling established that the gene was most highly expressed in the stem apex. The heterologous expression of CmTPL1-1 in Arabidopsis thaliana produced a pleiotropic phenotype, including smaller leaves, shorter siliques, increased meristem number, asymmetrical petal distribution and reduced stamen number. In transgenic plants, four AtARF s were downregulated, while six AtIAA s and two AtGH3 s were upregulated at the transcript level; moreover, the expression of three key class I KNOTTED-like homeobox (KNOX) genes was upregulated. In addition, by yeast two-hybrid screening of a chrysanthemum cDNA library, we found that CmTPL1-1 could interact with CmWOX4, CmLBD38 and CmLBD36, and these interactions were confirmed by bimolecular fluorescence complementation (BiFC) assays. Overall, we speculated that heterologous expression of CmTPL1-1 regulates plant growth and development by interacting with auxin signaling in Arabidopsis. • CmTPL1-1 showed no transcriptional activity and was localized in the nucleus. • The heterologous expression of CmTPL1-1 alters meristem maintenance and organ development in Arabidopsis thaliana. • Its heterologous expression down-regulated four AtARFs , while induced six AtIAAs , two AtGH3s and three class I KNOX genes. • Yeast two-hybrid and BiFC experimental results indicated that CmTPL1-1 can interact with CmWOX4, CmLBD38 and CmLBD36. [ABSTRACT FROM AUTHOR]

• 170 volatile compounds were detected in 41 tea chrysanthemum cultivars and hybrids. • The tea chrysanthemums could be separated into two groups based on their volatiles. • Several volatiles were found to be potential markers for future cultivar identification. • Three varieties were identified as potential donors for future quality improvement. • The findings help understand the diversity of volatiles and are conducive to developing new tea chrysanthemum varieties. Tea chrysanthemums generally have a distinctive and appealing aroma, which typically depends on the volatiles and affects the market share of different tea chrysanthemum varieties. Recently, many tea chrysanthemum cultivars and elite hybrids have been released for production. Therefore, understanding the diversity of the volatile compounds is critical to the quality improvement of tea chrysanthemums. Here, we studied the volatile compounds of 41 commercial tea chrysanthemum cultivars and elite hybrids using gas chromatography-mass spectrometry (GC-MS). One hundred and seventy volatile components were identified, of which 25 were species-specific, and palmitic acid was the only component present in all samples. Functional grouping divided the volatile components into 78 terpenoids, 15 hydrocarbons, 15 acids, 26 esters, 13 alcohols, 11 ketones, 3 aldehydes, and nine other compounds. There was a considerable variation in volatile compound contents among the investigated accessions, ranging from 481.04 ng/g of 'Suju-8' to 2495.67 ng/g of 'Suju-11'. A heatmap and dendrogram visualization suggested that the 41 tea chrysanthemums could be separated into two groups: commercial cultivars dominated one, while the other was composed mainly of elite hybrids. The principal component analysis found that 'Xiaohuangju', 'Zaohua-1', and 'CH7-18' had the best final scores with their special distinction in four principal component axes, and 'Suju-11' showed superiority in terpenoids, acids, esters, and ketones contents. The findings enable a better understanding of the composition of volatile compounds of tea chrysanthemums and are conducive to developing new varieties with superior volatiles in the future. [ABSTRACT FROM AUTHOR]

The nitrogen nutrition index (NNI) plays a critical role in improving crop nitrogen (N) diagnosis and predicting crop yield. Proximal sensing chlorophyll meters (CMs) have been widely used in precision agriculture, but few studies have focused on its utilization for estimating the NNI of chrysanthemum (Dendranthema morifolium Ramat.). This study aimed to develop a model for NNI estimation in chrysanthemums using CM readings. Field experiments were conducted with five N fertilization treatments during two growing seasons (in 2019 and 2020). Chrysanthemum canopies were sampled across multiple days after planting (DAP) to determine plant N concentrations (PNC) and plant dry matter (PDM). CM measurements were recorded at defined DAP at different leaf layer positions (L1, L2, and L3 represent leaves that were 1/3, 1/2, and 2/3 apart from the top of the plant, respectively), and the normalized CM index (NCMI 1 , NCMI 2 , and NCMI 3) was calculated. All PNC and PDM data from the two seasons were then applied to fit the critical N (N c) dilution curve using a Bayesian statistical model to estimate the NNI. Regression models were established to predict chrysanthemum NNI using CM readings and the NCMI as predictor variables. This study determined the N c of chrysanthemum to be N c = 2.318 ×PDM−0.204. L1 was found to be the optimal leaf layer position for NNI estimation. Additionally, the NCMI-based prediction of NNI was found to be more reliable than that from the CM readings. NCMI 1 was the best predictor of chrysanthemum NNI across multiple DAP (NNI = 0.0741 ×e2.6285NCMI1, coefficient of determination = 0.59***, root mean square error = 0.110 NNI). The findings of this study can be applied to accurately predict chrysanthemum NNI from CM readings to provide technical support for N nutrition diagnosis in chrysanthemums. • This is the first study establishing the critical N dilution curve in chrysanthemum. • The upper leaf layer is optimal for chrysanthemum N nutrition index (NNI) estimations. • The normalized chlorophyll meter index showed to be the best predictor of chrysanthemum NNI. [ABSTRACT FROM AUTHOR]

• The heredity of four intrinsic qualities, i.e., total flavone, chlorogenic acid, luteoloside, and isochlorogenic acid A, is first investigated in a segregating F1 population. • Transgressive individuals in both directions are observed for all quality traits, and a moderate-high heritability is at 0.57 ∼ 0.84. • Three improved hybrids of superior quality are identified for breeding use. • The findings are conducive to the breeding success of high-quality tea chrysanthemums. The active compounds in the dry head-like capitulum of tea chrysanthemums are essential contributors to human health. Therefore, increasing the internal quality is a critical aim of tea chrysanthemum breeding programs, and knowledge of the inheritance of the quality traits and accurate identification of elite hybrids is vital for breeding success. The heredity of four intrinsic qualities, i.e., total flavone, chlorogenic acid, luteoloside, and isochlorogenic acid A, were investigated in a segregating F 1 population. We implemented the principal components analysis (PCA), the membership function method, and hierarchical cluster analysis (HCA) to identify hybrids of superior quality. The quality traits were widely segregated, with the coefficient of variation ranging from 0.29 to 0.88. Transgressive individuals in both directions were observed for all investigated traits. Genotypes, environments, and genotype × environment interaction significantly affected the investigated compounds, and a moderate-high heritability was at 0.57 ∼ 0.84. Total flavone, luteoloside, and isochlorogenic acid A showed highly positive heterosis (P < 0.01), while chlorogenic acid demonstrated negative heterosis, and the heterosis ratio was separately estimated at 17.11%, 127.14%, 14.51%, and -9.10%. Moreover, three elite hybrids with a comprehensive evaluation value (D) larger than 0.8 were selected for breeding use. The current study's findings add a new understanding of the inheritance pattern of the investigated active compounds, and the production of improved hybrids represents an essential step towards developing high-quality tea chrysanthemums. [ABSTRACT FROM AUTHOR]

Salinity-stressed plants of salinity sensitive (‘Qx096’) and tolerant (‘Qx097’) chrysanthemum cultivar were treated with a range of concentrations of spermidine (Spd). Plant performance, as indicated by various parameters associated with growth, was improved by the treatment, as was the tissue content of soluble protein and proline. The extent of both Na + accumulation and K + loss was reduced. Activity levels of the stress-related enzymes SOD, POD, APX and CAT were significantly increased and the production of malondialdehyde (MDA) decreased. The suggestion was that treatment with 1.5 mM Spd would be an effective means alleviating salinity-stress induced injury through its positive effect on photosynthetic efficiency, reactive oxygen species scavenging ability and the control of ionic balance and osmotic potential. Its protective capacity was more apparent in ‘Qx096’ than in ‘Qx097’. [ABSTRACT FROM AUTHOR]

Members of the large WRKY transcription factor family are responsible for the regulation of plant growth, development and the stress response. Here, five WRKY members were isolated from chrysanthemum. They each contained a single WRKY domain and a C 2 H 2 zinc finger motif, so were classified into group II. Transient expression experiments demonstrated that all five were expressed in the nucleus, although CmWRKY42 was also expressed in the cytoplasm. When expressed heterologously in yeast, the products of CmWRKY22 and CmWRKY48 exhibited transactivation activity, while those of CmWRKY21 , CmWRKY40 and CmWRKY42 did not. The transcription of the five CmWRKY genes was profiled when the plants were challenged with a variety of abiotic and biotic stress agents, as well as being treated with various phytohormones. CmWRKY21 proved to be markedly induced by salinity stress, and suppressed by high temperature exposure; CmWRKY22 was induced by high temperature exposure; CmWRKY40 was highly induced by salinity stress, and treatment with either abscisic acid (ABA) or methyl jasmonate (MeJA); CmWRKY42 was up-regulated by salinity stress, low temperature, ABA and MeJA treatment and aphid infestation; CmWRKY48 was induced by drought stress, ABA and MeJA treatment and aphid infestation. The function of CmWRKY48 was further investigated by over-expressing it transgenically. The constitutive expression of this transcription factor inhibited the aphids' population growth capacity, suggesting that it may represent an important component of the plant's defense machinery against aphids. [ABSTRACT FROM AUTHOR]

Abstract: Anther wall development, microsporogenesis and microgametogenesis were compared between a normal male fertile chrysanthemum cultivar ‘NJAU04-29-2’ and the two male sterile selections ‘rm20-11’ (anther indehiscent) and ‘NJAU05-52-2’ (anther aborted). In both of the two male sterile types, the tapetum enlarged abnormally and showed signs of disorganization of walls at the onset of meiosis, the pollen was aborted, the anthers appeared shrunken, and the anther vascular bundle and connective tissue were degenerated by anthesis. In ‘rm20-11’, the two smaller pollen sacs began to degenerate at the microsporogenesis stage, so that only one or two microsporangia developed, while in ‘NJAU05-52-2’, only one or two microsporangia were formed following the archesporial cell stage, and most of the microspore mother cells degenerated during the course of meiosis. [ABSTRACT FROM AUTHOR]

• Inheritance of branching traits in chrysanthemum was dissected by QTL mapping under two contrasting densities. • Twelve and eight additive QTLs were uncovered under the low and high planting density regime conditions, respectively. • Two joint QTLs and four epistatic QTLs were detected. • Only one QTL, TsbnE1 × 4 or TsbnE2 × 4, was stable across two environments. The architecture of chrysanthemum plants raised for cut flowers is strongly influenced by their ability to form branches. The genetic basis of branching was revealed through a quantitative trait locus (QTL) analysis of an F 1 population generated by crossing the varieties 'Nannong Xuefeng' and 'Monalisa' grown under contrasting planting densities. Under the low planting density regime (E1), 12 additive QTLs involving seven branching-associated traits were detected, while under the high planting density regime (E2), the number of QTL detected was only eight. One of the individual QTL accounted for over 10% of the phenotypic variance. Of the 20 QTLs, only one was expressed under both high and low planting densities. A joint QTL analysis across the two environments identified two QTLs which were separately detected in E1. A set of four QTLs exhibiting additive × additive epistasis was identified, few of which had interaction with environments. [ABSTRACT FROM AUTHOR]