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The use of local native plant species for ecological restoration and rehabilitation is considered an important strategy for nature-based solutions. To achieve this goal, the key work is to understand the distribution of local native plants and their limiting factors. Pittosporum tobira is a keystone species of the vegetation community in subtropical coastal areas, and it plays an essential role in the function and stability of the coastal vegetation buffer zone. The aim of this study was to identify the factors that restrict the growth of P. tobira in the subtropical supratidal zone. We investigated the growth and development of P. tobira plants at three field sites, Dongtou Island (DT), Yuhuan Island (YH), and Cangnan County (CN), in Zhejiang Province, China. To investigate the key factors restricting the growth of this species, we sampled soils from both the supratidal zone and the P. tobira habitat zone. Soils in the supratidal zone showed typical characteristics of sodium chloride-type saline-alkali soil, and the soluble salts content showed wide fluctuations. Some soils in the supratidal zone showed severe salinization. The soil pH and soluble salts contents were higher, but soil organic matter content was lower, in the supratidal zone than in the P. tobira habitat zone. Among the three wild P. tobira habitat sites, DT had the lowest soil nutrient contents. In soil from the DT site, the soluble salts content was 150 % higher and soil organic matter content was 50 % lower than those in soils from the YH and CN sites. Compared with P. tobira growing at the CN and YH sites, those growing at the DT site showed higher antioxidant enzyme activity, higher organic osmotic regulatory substances content, and lower malondialdehyde content in the leaves and roots. These results suggest that the growth and distribution of P. tobira are affected by the organic matter content, pH, and soluble salts content in soil. Among the three P. tobira populations studied here, the population at DT was the most tolerant to the highly saline conditions in this subtropical coastal area, and has potential applications in landscape restoration of the supratidal zone.

Abstract Roses are consistently ranked at the forefront in cut flower production. Increasing demands of market and changing climate conditions have resulted in the need to further improve the diversity and quality of traits. However, frequent hybridization leads to highly heterozygous nature, including the allelic variants. Therefore, the absence of comprehensive genomic information leads to them making it challenging to molecular breeding. Here, two haplotype-resolved chromosome genomes for Rosa chinensis ‘Chilong Hanzhu’ (2n = 14) which is high heterozygous diploid old Chinese rose are generated. An amount of genetic variation (1,605,616 SNPs, 209,575 indels) is identified. 13,971 allelic genes show differential expression patterns between two haplotypes. Importantly, these differences hold valuable insights into regulatory mechanisms of traits. RcMYB114b can influence cyanidin-3-glucoside accumulation and the allelic variation in its promoter leads to differences in promoter activity, which as a factor control petal color. Moreover, gene family expansion may contribute to the abundance of terpenes in floral scents. Additionally, RcANT1, RcDA1, RcAG1 and RcSVP1 genes are involved in regulation of petal number and size under heat stress treatment. This study provides a foundation for molecular breeding to improve important characteristics of roses.

The double flower developmental process is regulated via a complex transcriptional regulatory network. To understand this highly dynamic and complex developmental process of Dianthus spp., we performed a comparative analysis of floral morphology and transcriptome dynamics in simple flowers and double flowers. We found that the primordium of double flowers of ‘X’ was larger in size compared to that of simple flowers of ‘L’ in Dianthus chinensis. RNA-seq and Weighted Gene Co-expression Network Analysis (WGCNA) during flower development, identified stage-specific gene network modules. Expression analysis by RNA-seq indicated that a group of genes related to floral meristem identity, primordia position and polarity were highly expressed in double flowers genotypes compared to simple flowers genotypes, suggesting their roles in double-petal formation. A total of 21 DEGs related to petal number were identified between simple and double flowers. The experiments of in situ hybridization revealed that DcaAP2L, DcaLFY and DcaUFO genes were expressed in the intra-sepal boundary and petal boundary. We proposed a potential transcriptional regulatory network for simple and double flower development. This study provides novel insights into the molecular mechanism underlying double flower formation in Dianthus spp.

Abstract Rose (Rosa) is a prominent ornamental plant that holds substantial economic and social significance. Roses originating from different regions exhibit intricate phenotypic and genetic characteristics, but the majority of rose genetic resources are poorly characterized. In this study, 192 genotypes of the genus Rosa were examined using 33 phenotypic traits and 10 pairs of SSR markers. Compared to wild species, both old garden and modern roses exhibited a significant level of diversity, with flower color having the highest degree of diversity and style morphology having the lowest degree of diversity. This phenomenon may be attributed to the limited utilization of wild roses due to their simpler ornamental traits and the frequent phenotypic and molecular infiltration between old garden roses and modern roses. Following a inaugural comprehensive evaluation employing principal component analysis, R. chinensis ‘Zihongxiang’, R. hybrida ‘Burgundy Iceberg’, R. hybrida ‘Conrad F. Meyer’, R. rugosa ‘Gaohong’ and R. floribunda ‘Sheherazad’ were selected as core germplasm resources for future breeding. Moreover, three tetraploid roses, namely R. hybrida ‘Midnight Blue’, R. floribunda ‘Sheherazad’, and R. hybrida ‘Couture Rose Tilia’, with significant differences in both phenotypic and molecular profiles were selected and reciprocally intercrossed. Ultimately, two populations were obtained exhibiting significant variation in flower size, annual stem color, stem pickle density, and leaf number. Furthermore, our results indicated that the traits of flower diameter, flower height, petal width, and petal number may potentially be controlled by two major-effect loci. In conclusion, this study provides novel insights into the evolutionary patterns of Rosa germplasm resources. It paves the way for identifying core genotypes that carry distinct ornamental characteristics and possess immense value for breeding novel varieties in the future.

Carnation (Dianthus caryophyllus L.) is a typical ethylene-sensitive cut flower. Variations in carnation vase life and sensitivity to ethylene have been reported, but no detailed analysis has been performed to date. In order to investigate the ethylene sensitivity of different cut carnation varieties and study the effect of ethylene on postharvest physiological changes of different carnation varieties, 14 varieties were used to explore ethylene sensitivity, and six varieties were used to analyze the release pattern of endogenous ethylene and the expression pattern of related genes. The results showed that among the 14 carnation varieties, 'Master' had the strongest ethylene sensitivity and 'Snow White' had the weakest ethylene sensitivity. Ethylene release changes of 'Master' are the terminal ascending type, and 'Cloud Shium', 'Little Pink', 'Seashell', 'Freedom' and 'Snow White' are the similar ethylene leap type. Ethylene biosynthesis genes DcACS1 and DcACO1 of 'Master' were up-regulated the most, and DcACO1 of 'Snow White' was the least up-regulated. The transient silencing and overexpression of DcACS1 and DcACO1 were performed and it was found that transient silencing can significantly delay aging, and overexpression significantly accelerates aging. This study laid the foundation for further research on the molecular mechanism of ethylene regulation of postharvest senescence of cut flowers of carnation, and also indicated the direction for further breeding and artificial screening of new storage tolerant carnation species by gene editing technology.

Carnation (Dianthus caryophyllus L.) is a typical ethylene-sensitive cut flower, but a few differences in ethylene sensitivity have been reported for different potted carnation species. In this study, we investigated the relationship between vase life, ethylene sensitivity, ethylene biosynthesis gene expression, and flower volatile substance content of 17 different potted carnation varieties. It was found that under the same post-harvest environmental conditions, the vase life of different varieties ranged from 6.2−14.2 d. Among the 17 varieties, 'Cherry' and 'Grace Bay' were highly sensitive to ethylene, and qRT-PCR analysis showed that their ethylene biosynthesis genes DcACS1 and DcACO1 expression increased the most, while 'Pink and Purple', 'Bondi Beach', and 'Grane Beach' showed the opposite pattern. In addition, the lower ethylene release was important in leading to longer vase life of potted carnations, and that ethylene release from shorter vase life varieties was 2.5−4.5 times greater than that of longer vase life varieties. Varieties that are more sensitive to ethylene are more likely to have a shorter vase life due to early disruption of water relations, which is mainly the result of reduced stem hydraulic conductivity and transpiration water loss. Analysis of volatile substances showed that ethylene had no significant effect on the release of volatile substances from potted carnations. Therefore, a better understanding of petal senescence in potted carnations will help us to improve measures to extend flower longevity according to the ethylene sensitivity of different varieties.

The SEPALLATA (SEP) gene, as a 'glue' for the 'floral quartets model', plays an important role in floral organ development by forming tetramers with class A-, B-, and C- genes. The functional differentiation of class E genes has been reported in different species. Carnation (Dianthus spp.) is a world-famous economic flower that has been extensively used in landscaping, but the roles of SEP genes in carnation are unclear. Here, we found that the class E genes of D. chinensis cultivar 'L' showed different expression patterns during floral organ primordium development by transcriptome analysis. Combined with quantitative real-time PCR, its tissue and specific stage expression patterns were also different in different subclades. In addition, a yeast two-hybrid experiment was carried out to explore the interaction patterns of class E genes with other class A-, B-, and C- genes. Only DcSEP3s and DcSEP4s proteins interacted with all three classes of A-, B-, and C- proteins, and interestingly, is that DcSEP3-1 only interacted with the DcAP1 protein of class A, while the DcSEP3-2 protein only interacted with DcFUL1. Transgenic experiments showed that overexpression of DcSEP3-2 genes in Arabidopsis resulted in early flowering, smaller rosettes, dwarfism and abnormal floral organs. The transgenic line overexpressing of DcSEP3-1 only showed an early flowering phenotype. All these results indicated that the two DcSEP3s of class E genes in D. chinensis may undergo sub-functionalization. These findings advance our understanding of the molecular mechanisms of flower development in carnation.

Abstract Background Prunus mume is an early spring flower of Rosaceae, which owns high application value in gardens. Being an excellent ornamental trait, the double flower trait has always been one of the important breeding goals of plant breeders. However, the key regulatory genes of double flower traits of P. mume are still unclear at present. Results The floral organs’ morphological differences of 20 single and 20 double flower cultivars of P. mume were compared firstly. And it was found that double flower trait of P. mume were often accompanied by petaloid stamen, multiple carpels and an increase in the total number of floral organs. Then, transcriptome sequencing of two representative cultivars P. mume ‘Danban Lve’ and P. mume ‘Xiao Lve’ were conducted at 3 Stage of flower bud development with distinct morphological differentiation. 3256 differentially expression genes (DEGs) were detected, and 20 candidate genes for double flower trait of P. mume were screened out including hub genes PmAP1–1 and PmAG-2 based on DEGs function analysis and WGCNA analysis. And it was found that epigenetic and hormone related genes may also play an important role in the process of double flower. Conclusions This study suggested that the double flower trait of P.mume is more like accumulation origin based on morphological observation. 20 genes and co-expression network related to the formation of double flower P. mume were preliminarily screened through transcriptomics analysis. The results provided a reference for further understanding of the molecular mechanism of double flower trait in P. mume.

The basic helix-loop-helix (bHLH) transcription factor family is the second-largest family in plants, where it plays essential roles in development, and the responses to multiple abiotic and biotic stressors. However, little information is available about this gene family in Prunus mume, which is widely cultivated in East Asia as an ornamental fruit tree. Here, 100 PmbHLH genes were identified, and their evolution and functions were explored in P. mume for the first time. The PmbHLH genes were classified into 21 subfamilies. The chromosomal distribution, physicochemical properties, bHLH domain, conserved motif, and intron/exon compositions were also analyzed. Furthermore, the evolutionary pattern, divergence time of the PmbHLH family, and genetic relationships among P. mume, Arabidopsis thaliana, and Prunus persica and Fragaria vesca of Rosaceae were explored. The functional prediction analysis of these PmbHLHs indicated that their functions varied, and included participating in the formation of organs and tissues, responding to stress, and the biosynthesis and metabolism of hormones and other secondary metabolites. Interestingly, expression analyses of PmbHLHs also revealed diverse expression patterns. Most of the PmbHLH genes were highly expressed in roots and stems, and a few were highly expressed in leaves, buds, and fruits, indicating tissue expression specificity. Eight PmbHLH genes, which were upregulated during low-temperature stress, may have critical roles in the response to cold stress. Ten PmbHLHs were differentially expressed between weeping and upright branches in a P. mume F1 population. These results shed light on the structure and evolution of the PmbHLH gene family, and lay a foundation for further functional studies of the bHLH genes.

Rose is sensitive to high temperature which will make the rose go into a semi-dormancy state. Grafting is an excellent way to enhance rose heat tolerance. Here, heat-tolerant Rosa multiflora ‘Huanong Wuci 1′ (W) and heat-sensitive Rosa chinensis ‘Old Blush’ (X) were selected as experimental materials. The RNA-seq technique was used to investigate the transcriptomes of self-root grafting line (XX0), heterogeneous grafting line (XW0), self-root grafting line under 6 h heat stress (XX6), and heterogeneous grafting line under 6 h heat stress (XW6). Under high temperature stress, multiple signaling pathways were activated, moreover, a large number of transcription factors and functional genes were induced, especially the HSFs and HSPs with remarkably upregulated expression levels. The GO analysis showed that the differences in the expressions of the genes related to fatty acids and carbohydrates were observed between self-root grafting line and heterogeneous grafting line. In addition, 14 P450s were differentially expressed, and one lectin gene was up-regulated in XW0 vs XW6, but down-regulated in XX0 vs XX6. Considering physiological and biochemical traits such as relative electrolyte leakage, SOD activity, proline, and total soluble sugars, DEGs involved in these processes may be key factors to resist high temperature. The present study provides an insight into the complex mechanism underlying grafting in response to heat stress. Our results indicate that grafting is an effective way to improve rose heat resistance.

Abstract Background AGAMOUS (AG) subfamily genes regulate the floral organs initiation and development, fruit and seed development. At present, there has been insufficient study of the function of AG subfamily genes in Asteraceae. Marigold (Tagetes erecta) belongs to Asteraceae family whose unique inflorescence structure makes it an important research target for understanding floral organ development in plants. Results Four AG subfamily genes of marigold were isolated and phylogenetically grouped into class C (TeAG1 and TeAG2) and class D (TeAGL11–1 and TeAGL11–2) genes. Expression profile analysis demonstrated that these four genes were highly expressed in reproductive organs of marigold. Subcellular localization analysis suggested that all these four proteins were located in the nucleus. Protein-protein interactions analysis indicated that class C proteins had a wider interaction manner than class D proteins. Function analysis of ectopic expression in Arabidopsis thaliana revealed that TeAG1 displayed a C function specifying the stamen identity and carpel identity, and that TeAGL11–1 exhibited a D function regulating seed development and petal development. In addition, overexpression of both TeAG1 and TeAGL11–1 leaded to curling rosette leaf and early flowering in Arabidopsis thaliana. Conclusions This study provides an insight into molecular mechanism of AG subfamily genes in Asteraceae species and technical support for improvement of several floral traits.

Abstract Background The ALOG (Arabidopsis LSH1 and Oryza G1) family of proteins, namely DUF640 (domain of unknown function 640) domain proteins, were found in land plants. Functional characterization of a few ALOG members in model plants such as Arabidopsis and rice suggested they play important regulatory roles in plant development. The information about its evolution, however, is largely limited, and there was no any report on the ALOG genes in Petunia, an important ornamental species. Results The ALOG genes were identified in four species of Petunia including P. axillaris, P. inflata, P. integrifolia, and P. exserta based on the genome and/or transcriptome databases, which were further confirmed by cloning from P. hybrida ‘W115’ (Mitchel diploid), a popular laboratorial petunia line susceptible to genetic transformation. Phylogenetic analysis indicated that Petunia ALOG genes (named as LSHs according to their closest Arabidopsis homologs) were grouped into four clades, which can be further divided into eight groups, and similar exon-intron structure and motifs are reflected in the same group. The PhLSH genes of hybrid petunia ‘W115’ were mainly derived from P. axillaris. The qPCR analysis revealed distinct spatial expression patterns among them suggesting potentially functional diversification. Moreover, over-expressing PhLSH7a and PhLSH7b in Arabidopsis uncovered their functions in the development of both vegetative and reproductive organs. Conclusions Petunia genome includes 11 ALOG genes that can be divided into eight distinct groups, and they also show different expression patterns. Among these genes, PhLSH7b and PhLSH7a play significant roles in plant growth and development, especially in fruit development. Our results provide new insight into the evolution of ALOG gene family and have laid a good foundation for the study of petunia LSH gene in the future.

Abstract Sweetgums (Liquidambar), members of the family Altingiaceae (Altingiales), have inflorescences and floral organs that are distinctive in structure compared with other angiosperms in which the roles of floral homeotic genes have been studied. To begin to understand the role of AGAMOUS (AG)—a floral homeotic gene that has a major role in stamen and carpel development—in development of the monosexual flowers of sweetgum, we used RNAi to reduce the expression of two members of the AG subfamily. Because AG suppression should induce floral sterility, RNAi might also provide a tool to mitigate the risks of invasiveness—and to reduce the production of its nuisance fruits or allergenic pollen—when sweetgum is used as an exotic shade or forest tree. We tested 33 independent transgenic events and non‐transgenic controls during 10 years in the field. The RNAi‐AG sweetgum trees maintained normal growth, phenology, and vivid fall coloration during the 10 years of study, but 8 insertion events had highly modified inflorescence and floral morphology. The modified flowers had anthers and carpels that were converted to flat leaf‐like structures lacking pollen grains and ovules, respectively. The female inflorescences developed into dry papery structures that failed to produce seeds. These infructescences were smaller than control infructescences, and lost a greater percentage of biomass in a controlled decay assay. RNAi against AG genes was highly effective at impairing fertility and modifying reproductive development without significant vegetative effects in sweetgum and gave phenotypes distinct from, but similar to, that of AG loss of function in other angiosperms.

Abstract Background SQUAMOSA PROMOTER BINDING PROTEIN (SBP)-box genes encode a family of plant-specific transcription factors (TFs) that play important roles in many growth and development processes including phase transition, leaf initiation, shoot and inflorescence branching, fruit development and ripening etc. The SBP-box gene family has been identified and characterized in many species, but has not been well studied in Petunia, an important ornamental genus. Results We identified 21 putative SPL genes of Petunia axillaris and P. inflata from the reference genome of P. axillaris N and P. inflata S6, respectively, which were supported by the transcriptome data. For further confirmation, all the 21 genes were also cloned from P. hybrida line W115 (Mitchel diploid). Phylogenetic analysis based on the highly conserved SBP domains arranged PhSPLs in eight groups, analogous to those from Arabidopsis and tomato. Furthermore, the Petunia SPL genes had similar exon-intron structure and the deduced proteins contained very similar conserved motifs within the same subgroup. Out of 21 PhSPL genes, fourteen were predicted to be potential targets of PhmiR156/157, and the putative miR156/157 response elements (MREs) were located in the coding region of group IV, V, VII and VIII genes, but in the 3’-UTR regions of group VI genes. SPL genes were also identified from another two wild Petunia species, P. integrifolia and P. exserta, based on their transcriptome databases to investigate the origin of PhSPLs. Phylogenetic analysis and multiple alignments of the coding sequences of PhSPLs and their orthologs from wild species indicated that PhSPLs were originated mainly from P. axillaris. qRT-PCR analysis demonstrated differential spatiotemperal expression patterns of PhSPL genes in petunia and many were expressed predominantly in the axillary buds and/or inflorescences. In addition, overexpression of PhSPL9a and PhSPL9b in Arabidopsis suggested that these genes play a conserved role in promoting the vegetative-to-reproductive phase transition. Conclusion Petunia genome contains at least 21 SPL genes, and most of the genes are expressed in different tissues. The PhSPL genes may play conserved and diverse roles in plant growth and development, including flowering regulation, leaf initiation, axillary bud and inflorescence development. This work provides a comprehensive understanding of the SBP-box gene family in Petunia and lays a significant foundation for future studies on the function and evolution of SPL genes in petunia.

Prunus mume is a traditional ornamental plant, which owed a unique floral scent. However, the diversity of the floral scent in P. mume cultivars with different aroma types was not identified. In this study, the floral scent of eight P. mume cultivars was studied using headspace solid-phase microextraction (HS-SPME) and organic solvent extraction (OSE), combined with gas chromatography-mass spectrometry (GC-MS). In total, 66 headspace volatiles and 74 endogenous extracts were putatively identified, of which phenylpropanoids/benzenoids were the main volatile organic compounds categories. As a result of GC-MS analysis, benzyl acetate (1.55–61.26%), eugenol (0.87–6.03%), benzaldehyde (5.34–46.46%), benzyl alcohol (5.13–57.13%), chavicol (0–5.46%), and cinnamyl alcohol (0–6.49%) were considered to be the main components in most varieties. However, the volatilization rate of these main components was different. Based on the variable importance in projection (VIP) values in the orthogonal partial least-squares discriminate analysis (OPLS-DA), differential components of four aroma types were identified as biomarkers, and 10 volatile and 12 endogenous biomarkers were screened out, respectively. The odor activity value (OAV) revealed that several biomarkers, including (Z)-2-hexen-1-ol, pentyl acetate, (E)-cinnamaldehyde, methyl salicylate, cinnamyl alcohol, and benzoyl cyanide, contributed greatly to the strong-scented, fresh-scented, sweet-scented, and light-scented types of P. mume cultivars. This study provided a theoretical basis for the floral scent evaluation and breeding of P. mume cultivars.

The transcriptional activation of heat shock proteins (Hsps) by heat shock transcription factors (Hsfs) is presumed to have a pivotal role in plant heat stress (HS) response. Prunus mume is an ornamental woody plant with distinctive features, including rich varieties and colors. In this study, 18 Hsfs and 24 small Hsps (sHsps) were identified in P. mume. Their chromosomal locations, protein domains, conserved motifs, phylogenetic relationships, and exon–intron structures were analyzed and compared with Arabidopsis thaliana Hsfs or sHsps. A total of 18 PmHsf members were classified into three major classes, A, B, and C. A total of 24 PmsHsps were grouped into eight subfamilies (CI to CIII, P, endoplasmic reticulum, M, and CI- or P-related). Quantitative reverse transcription PCR analysis revealed that members of the A2, A7, and A9 groups became the prominent Hsfs after heat shock, suggesting their involvement in a key regulatory role of heat tolerance. Most of the PmsHsp genes were up-regulated upon exposure to HS. Overall, our data contribute to an improved understanding of the complexity of the P. mume Hsf and sHsp gene families, and provide a basis for directing future systematic studies investigating the roles of the Hsf and sHsp gene families.

Tagetes erecta is an annual multifunctional plant which can be cultivated under a broad range of climatic conditions. Polyploidization and interspecific hybridization are applied to facilitate breeding cultivars of T. erecta with improved ornamental qualities. Colchicine treatment to the germinating seeds was proved to be a useful tool for chromosome doubling of the male sterile two-type line ‘M525AB’, with the resulting frequency of polyploid seedlings ranging from 88.89% (following 0.05% w/v colchicine applied for a 3–6 h exposure period) to a maximum of 100.00% (following 0.1% for 3–6 h, or 0.2% for 3 h). Morphological observation, stomatal size and density analysis, flow cytometric analysis and chromosome counting were conducted to identify the tetraploid plants. Distinctive morphological changes were observed in a notable proportion of polyploid plants. The colchicine-treated polyploid T. erecta plants showed dwarfed and more robust growth, thicker, larger and greener leaves, larger inflorescences and florets. The mutant plants identified through morphological observation all aligned as polyploid plants, thus morphological observation could be an effective method for the detection of polyploidy. The polyploid plants had significant larger stomata size over the abaxial leaf surface, whereas the density of stomata distribution was remarkably reduced. The survival rate of tetraploid cuttings (i.e. 38%) was greatly reduced compared to that of diploid plants. The fertility of tetraploid plants was also decreased, as shown by cross-pollination yields. Interspecific hybridizations between colchicine-induced tetraploid plants of a male sterile T. erecta line and the naturally tetraploid fully fertile Tagetes patula species resulted in hybrid progeny. Most of these hybrids displayed the dwarfed growth stature and compact, larger-flower morphology which is the typical ideotype of herbaceous flowers. Thus, polyploidization may be employed effectively as a means to facilitate interspecific hybridization, thereby contributing significantly to the improvement of quantitative traits of Tagetes spp.

Flowers with more petals are of more ornamental value. It is well known that AGAMOUS (AG) is the core member of the C-class gene which plays an essential role in double flower formation and identification of stamens and carpels in Arabidopsis thaliana. We searched C-class genes in the genome of the carnation, and found two AG orthologs (DcaAGa, DcaAGb). Phylogenetic analysis showed that the two genes were closely related to the euAG subclade. Then we searched the genomes of other Caryophyllales plants (Beta vulgaris, Spinacia oleracea, Chenopodium quinoa) for C-class genes, and found that their C-class genes all belonged to the euAG subclade. Semi-quantitative PCR (sq-PCR) analysis indicated that the expression of DcaAG genes in the single flower phenotype was higher than that in the double flower phenotype. Quantitative real-time RT-PCR (qRT-PCR) analysis showed that the expressions of DcaAG genes in the flower bud were significantly different from those in the root, stem, and leaf between the single and double flower phenotype carnations, and that DcaAG genes were specifically expressed in the stamen and carpel of carnation. Moreover, the expression of other floral organ identity genes (AP1 and AP2, PI and AP3, SEP1 and SEP3 corresponding to the A-, B-, and E-class of genes, respectively) showed no significant difference in all floral organs between the single and double flower phenotype carnations, suggesting that C-class (DcaAG) genes might play an important role in the double flower phenotype in carnation. Petal loss or decrease, precocious flowering, silique shortening, and seed sterility were observed in 35S::DcaAGa and 35S::DcaAGb transgenic Arabidopsis plants. All these results show that DcaAG genes might affect the petal number negatively and have a specific function in stamen and carpel development in carnation.

FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) proteins share highly conserved amino acid residues but they play opposite regulatory roles in promoting and repressing the flowering response, respectively. Previous substitution models and functional analysis have identified several key amino acid residues which are critical for the promotion of flowering. However, the precise relationship between naturally occurring FT/TFL1 homologs and the mechanism of their role in flowering is still unclear. In this study, FT/TFL1 homologs from eight Rosaceae species, namely, Spiraea cantoniensis, Pyracantha fortuneana, Photinia serrulata, Fragaria ananassa, Rosa hybrida, Prunus mume, Prunus persica and Prunus yedoensis, were isolated. Three of these homologs were further characterized by functional analyses involving site-directed mutagenesis. The results showed that these FT/TFL1 homologs might have diverse functions despite sharing a high similarity of sequences or crystal structures. Functional analyses were conducted for the key FT amino acids, Tyr-85 and Gln-140. It revealed that TFL1 homologs cannot promote flowering simply by substitution with key FT amino acid residues. Mutations of the IYN triplet motif within segment C of exon 4 can prevent the FT homolog from promoting the flowering. Furthermore, physical interaction of FT homologous or mutated proteins with the transcription factor FD, together with their lipid-binding properties analysis, showed that it was not sufficient to trigger flowering. Thus, our findings revealed that the divergence of flowering time modulating by FT/TFL1 homologs is independent to interaction and binding activities.

According to the floral organ development ABC model, B class genes specify petal and stamen identification. In order to study the function of B class genes in flower development of Tagetes erecta, five MADS-box B class genes were identified and their expression and putative functions were studied. Sequence comparisons and phylogenetic analyses indicated that there were one PI-like gene-TePI, two euAP3-like genes-TeAP3-1 and TeAP3-2, and two TM6-like genes-TeTM6-1 and TeTM6-2 in T. erecta. Strong expression levels of these genes were detected in stamens of the disk florets, but little or no expression was detected in bracts, receptacles or vegetative organs. Yeast hybrid experiments of the B class proteins showed that TePI protein could form a homodimer and heterodimers with all the other four B class proteins TeAP3-1, TeAP3-2, TeTM6-1 and TeTM6-2. No homodimer or interaction was observed between the euAP3 and TM6 clade members. Over-expression of five B class genes of T. erecta in Nicotiana rotundifolia showed that only the transgenic plants of 35S::TePI showed altered floral morphology compared with the non-transgenic line. This study could contribute to the understanding of the function of B class genes in flower development of T. erecta, and provide a theoretical basis for further research to change floral organ structures and create new materials for plant breeding.

Tagetes erecta is an important commercial plant of Asteraceae family. The male sterile (MS) and male fertile (MF) two-type lines of T. erecta have been utilized in F1 hybrid production for many years, but no report has been made to identify the genes that specify its male sterility that is caused by homeotic conversion of floral organs. In this study, transcriptome assembly and digital gene expression profiling were performed to generate expression profiles of MS and MF plants. A cDNA library was generated from an equal mixture of RNA isolated from MS and MF flower buds (1 mm and 4 mm in diameter). Totally, 87,473,431 clean tags were obtained and assembled into 128,937 transcripts among which 65,857 unigenes were identified with an average length of 1,188 bp. About 52% of unigenes (34,176) were annotated in Nr, Nt, Pfam, KOG/COG, Swiss-Prot, KO (KEGG Ortholog database) and/or GO. Taking the above transcriptome as reference, 125 differentially expressed genes were detected in both developmental stages of MS and MF flower buds. MADS-box genes were presumed to be highly related to male sterility in T. erecta based on histological and cytological observations. Twelve MADS-box genes showed significantly different expression levels in flower buds 4 mm in diameter, whereas only one gene expressed significantly different in flower buds 1 mm in diameter between MS and MF plants. This is the first transcriptome analysis in T. erecta and will provide a valuable resource for future genomic studies, especially in flower organ development and/or differentiation.

The identification of mutants in model plant species has led to the isolation of the floral homeotic function genes that play crucial roles in flower organ specification. However, floral homeotic C-function genes are rarely studied in basal eudicots. Here, we report the isolation and characterization of the AGAMOUS (AG) orthologous gene (PaAG) from a basal eudicot London plane tree (Platanus acerifolia Willd). Phylogenetic analysis showed that PaAG belongs to the C- clade AG group of genes. PaAG was found to be expressed predominantly in the later developmental stages of male and female inflorescences. Ectopic expression of PaAG-1 in tobacco (Nicotiana tabacum) resulted in morphological alterations of the outer two flower whorls, as well as some defects in vegetative growth. Scanning electron micrographs (SEMs) confirmed homeotic sepal-to-carpel transformation in the transgenic plants. Protein interaction assays in yeast cells indicated that PaAG could interact directly with PaAP3 (a B-class MADS-box protein in P. acerifolia), and also PaSEP1 and PaSEP3 (E-class MADS-box proteins in P. acerifolia). This study performed the functional analysis of AG orthologous genes outside core eudicots and monocots. Our findings demonstrate a conserved functional role of AG homolog in London plane tree, which also represent a contribution towards understanding the molecular mechanisms of flower development in this monoecious tree species.

Whole-genome duplication (WGD; i.e., polyploidy) and chromosomal rearrangement (i.e., genome shuffling) significantly influence genome structure and organization. Many polyploids show extensive genome shuffling relative to their pre-WGD ancestors. No reference genome is currently available for Platanaceae (Proteales), one of the sister groups to the core eudicots. Moreover, Platanus × acerifolia (London planetree; Platanaceae) is a widely used street tree. Given the pivotal phylogenetic position of Platanus and its 2-y flowering transition, understanding its flowering-time regulatory mechanism has significant evolutionary implications; however, the impact of Platanus genome evolution on flowering-time genes remains unknown. Here, we assembled a high-quality, chromosome-level reference genome for P. × acerifolia using a phylogeny-based subgenome phasing method. Comparative genomic analyses revealed that P. × acerifolia (2n = 42) is an ancient hexaploid with three subgenomes resulting from two sequential WGD events; Platanus does not seem to share any WGD with other Proteales or with core eudicots. Each P. × acerifolia subgenome is highly similar in structure and content to the reconstructed pre-WGD ancestral eudicot genome without chromosomal rearrangements. The P. × acerifolia genome exhibits karyotypic stasis and gene sub-/neo-functionalization and lacks subgenome dominance. The copy number of flowering-time genes in P. × acerifolia has undergone an expansion compared to other noncore eudicots, mainly via the WGD events. Sub-/neo-functionalization of duplicated genes provided the genetic basis underlying the unique flowering-time regulation in P. × acerifolia. The P. × acerifolia reference genome will greatly expand understanding of the evolution of genome organization, genetic diversity, and flowering-time regulation in angiosperms. [ABSTRACT FROM AUTHOR]