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Background Cultivated Hippeastrum × hybridum is a popular ornamental plant with large and colorful flowers, long flowering duration, and high commercial value. As its main ornamental feature, its flower color is related to the anthocyanin content in the tepals. However, the molecular regulatory mechanisms of anthocyanin biosynthesis in H . × hybridum have not yet been elucidated. Results In the present study, 12 cDNA libraries of four stages of H. × hybridum ‘Royal Velvet’ tepal development were used for RNA-seq, obtaining 79.83 gigabases (GB) of clean data. The data were assembled into 148,453 unigenes, and 11,262 differentially expressed genes were identified. Forty key enzymes participating in anthocyanin biosynthesis were investigated, and the results showed that most of the anthocyanin structural genes were expressed at low levels in S1 and were markedly upregulated in S2 and S3. The expression profiles of 12 selected genes were verified by qRT-PCR. Furthermore, the R2R3-MYB transcription factor (TF), HpMYB1 , involved in the regulation of anthocyanin biosynthesis was identified by sequence, expression pattern, and subcellular localization analyses. Its overexpression in tobacco significantly increased the anthocyanin levels in various tissues and activated anthocyanin-related genes. Conclusions Using RNA-seq technology, we successfully identified a potential R2R3-MYB gene, HpMYB1 , that regulates anthocyanin biosynthesis in H. × hybridum ‘Royal Velvet’. Our findings provide basic transcript information and valuable transcriptome data for further identification of key genes involved in anthocyanin biosynthesis and can be applied in the artificial breeding of new H . × hybridum cultivars with enhanced ornamental value.

Key message The Montgomery equation, which assumes a proportional relationship between the tepal area and the product of the tepal length and width, is validated using data drawn from four Magnolia species. An important metric of floral non-reproductive size is individual petal or tepal area ( A ). The Montgomery equation (ME) estimates A by assuming a proportional relationship between A and the product of petal or tepal length ( L ) and width ( W ), i.e., A ∝ L W , whereas the power-law equation (PLE) assumes the allometric relationship A ∝ LW α 1 ≠ 1 . If W/L has a small variation, four relationships are expected to hold true, i.e., A ∝ L 2 , A ∝ L α 2 , A ∝ W 2 , and A ∝ W α 3 , where α 1 , α 2 , and α 3 are scaling exponents to be estimated. To assess the validity of these six formulae, 2031 the petal-like tepals of 250 flowers from four Magnolia species were measured. The root-mean-square error (RMSE) was used to determine the goodness of fit of each equation, and the percentage error (PE) was used to compare any two equations with the same predicator, i.e., LW , L and W . The ME was validated for calculating A at the species level and for the pooled data given that three of the four species had < 0.05 RMSEs and one had a < 0.07 RMSE. However, the PLE was more robust than the ME at the species level. For the pooled data, the ME and PLE had a negligible difference in RMSE values. These results show that the ME is a valid and non-destructive tool for measuring A for the Magnolia species examined in this study and likely holds true across other more diverse species.

Gloriosa L. possesses exceptional ornamental value, with its floral hues exhibiting a wide range of variations. In this study, we employed sophisticated colorimetry, Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS), and transcriptome sequencing to investigate the phenotypic expression of tepal colors, the composition of carotenoids and anthocyanins, and the differential gene expression in four Gloriosa varieties during their full bloom phase. Our findings revealed that the redness of the tepals, indicated by higher a * values, increased with the intensity of the red hue, while lighter colors corresponded to higher L * values. Metabolomic analysis identified 50 carotenoids and 60 anthocyanins. It was observed that carotenoids primarily influence the yellow and orange color of Gloriosa tepals, with β -carotene, lutein, and zeaxanthin being the predominant carotenoids. Anthocyanins serve as the principal coloring agents in the orange, red and purple tepals of Gloriosa . High levels and proportions of cyanidins and pelargonidins are key contributors to the formation of red and purple tepals, while high levels and proportions of peonidins also play a significant role in purple coloration. In contrast, the presence of high levels and proportions of pelargonidins alone is a crucial factor in the formation of orange tepals. Transcriptomic data unearthed 57 and 92 candidate differentially expressed genes (DEGs) belong to carotenoid and anthocyanin biosynthesis pathway, respectively, with PSY , PDS , DFR , and ANS genes considered as critical genes for the differential accumulation of pigments of Gloriosa tepals. Weighted gene co-expression network analysis (WGCNA) revealed significant co-expression patterns between 217 transcription regulatory factors (TFs) and 8 carotenoid biosynthesis genes, and between 194 TFs and 41 anthocyanin biosynthesis genes. qRT-PCR verified the expression patterns of four carotenoid biosynthesis-related genes, eight anthocyanin biosynthesis-related genes, and three transcription regulatory factors. It was found that Cluster-121969.6 ( MYB ) gene is specifically expressed in the tepals of the four varieties (compared to stems and leaves) and shows a high consistency with the trend of anthocyanin content changes. This research provides new insights into the mechanisms underlying the formation of diverse floral colors in Gloriosa tepals.

Key messageA significant scaling relationship between the perianth mass and area was detected using 306 flowers of Magnolia × soulangeana, and increases in mass failed to achieve proportional increases in area.The scaling relationship between leaf lamina mass and area has been explored extensively. However, this relationship for floral parts, which are considered homologous with foliage leaves, has not been studied despite the implications of scaling theory and plant morphometry. Toward this goal, a total of 306 flowers and 2759 tepals of Magnolia × soulangeana were collected and measured. The area of each tepal was determined by digitizing its profile, and the perianth area (Ap) was empirically determined by summing the areas of all tepals per flower. The perianth fresh mass (FM) was also measured, and the Montgomery equation (ME) was used to estimate the tepal area (At) predicted as proportional to the product of tepal length (L) and width (W) to explore the feasibility of estimating At non-destructively. The scaling exponent of FM vs Ap significantly exceeded unity, i.e., increases in mass failed to achieve proportional increases in area, a phenomenon called “diminishing returns”. The estimated proportionality coefficient of ME for non-destructively calculating At approximately equaled 0.7 [i.e., At ≈ (3/4)LW], and the distributions of At, L, W/L, and the tepal centroid ratio were relatively concentrated. The data indicate that (1) scaling relationship between tepal mass and area is statistically indistinguishable from the phenomenon observed for foliage leaves, (2) tepal shape and leaf shape are similar, and (3) the ME predicts tepal area nondestructively. These results encourage the application of the ME to study tepal shape and geometry and support the serial homology between leaves and tepals for this Magnolia hybrid.

Many angiosperm families develop spatially regulated anthocyanin spots on their flowers. The Asiatic hybrid lily (Lilium spp.) cv ‘Latvia’ develops splatter-type spots on its tepals. The splatters arise simply from the deposition of anthocyanin pigments in the tepal epidermis. To determine how splatter development was regulated, we analysed the transcription of anthocyanin biosynthesis genes, and isolated and characterized an R2R3-MYB gene specific to splatter pigmentation. All anthocyanin biosynthesis genes were expressed in splatter-containing regions of tepals, but not in other regions, indicating that splatter pigmentation is caused by the transcriptional regulation of biosynthesis genes. Previously characterized LhMYB12 regulators were not involved in splatter pigmentation, but, instead, a new allele of the LhMYB12 gene, LhMYB12-Lat, isolated in this study, contributed to splatter development. In ‘Latvia’ and other lily plants expressing splatters, LhMYB12-Lat was preferentially transcribed in the splatter-containing region of tepals. Progeny segregation analysis showed that LhMYB12-Lat genotype and splatter phenotype were co-segregated among the F1 population, indicating that LhMYB12-Lat determines the presence or absence of splatters. LhMYB12-Lat contributes to splatter development, but not to full-tepal pigmentation and raised spot pigmentation. As a result of its unique sequences and different transcription profiles, this new allele of LhMYB12 should be a novel R2R3-MYB specifically associating with splatter spot development.

Background A puzzle in evolution is the understanding of how the environment might drive subtle phenotypic variation, and whether this variation is adaptive. Under the neutral evolutionary theory, subtle phenotypes are almost neutral with little adaptive value. To test this idea, we studied the infraspecific variation in flower shape and color in Mammillaria haageana , a species with a wide geographical distribution and phenotypic variation, which populations are often recognized as infraspecific taxa. Results We collected samples from wild populations, kept them in the greenhouse for at least one reproductive year, and collected newly formed flowers. Our first objective was to characterize tepal natural variation in M. haageana through geometric morphometric and multivariate pigmentation analyses. We used landmark-based morphometrics to quantify the trends of shape variation and tepal color-patterns in 20  M. haageana accessions, belonging to five subspecies, plus 8  M. albilanata accessions for comparison as the sister species. We obtained eight geometric morphometric traits for tepal shape and color-patterns. We found broad variation in these traits between accessions belonging to the same subspecies, without taxonomic congruence with those infraspecific units. Also the phenetic cluster analysis showed different grouping patterns among accessions. When we correlated these phenotypes to the environment, we also found that solar radiation might explain the variation in tepal shape and color, suggesting that subtle variation in flower phenotypes might be adaptive. Finally we present anatomical sections in M. haageana subsp.  san-angelensis to propose some of the underlying tepal structural features that may give rise to tepal variation. Conclusions Our geometric morphometric approach of flower shape and color allowed us to identify the main trends of variation in each accession and putative subspecies, but also allowed us to correlate these variation to the environment, and propose anatomical mechanisms underlying this diversity of flower phenotypes.

Allium mardinense Balos, H. Akan & Yıldırım, a new species of Allium sect. Allium, is described from Mardin Province, southeastern Turkey. It resembles A. aybukeae and A. enginii but differs from them by several morphological characters, such as its filament length, inner tepal shape and surface, and anther colour. Diagnostic characters, a comprehensive description, photographs, and a distribution map of A. mardinense are provided.

Main conclusionIn Magnolia polytepala, the formation of floral organization and color was attributed to tissue-dependent differential expression levels of MADS-box genes and anthocyanin biosynthetic genes.In angiosperms, the diversity of floral morphology and organization suggests its value in exploring plant evolution. Magnolia polytepala, an endemic basal angiosperm species in China, possesses three green sepal-like tepals in the outermost whorl and pink petal-like tepals in the inner three whorls, forming unique floral morphology and organization. However, we know little about its underlying molecular regulatory mechanism. Here, we first reported the full-length transcriptome of M. polytepala using PacBio sequencing. A total of 16 MADS-box transcripts were obtained from the transcriptome data, including floral homeotic genes (e.g., MpAPETALA3) and other non-floral homeotic genes (MpAGL6, etc.). Phylogenetic analysis and spatial expression pattern reflected their putative biological function as their homologues in Arabidopsis. In addition, nine structural genes involved in anthocyanin biosynthesis pathway had been screened out, and tepal color difference was significantly associated with their tissue-dependent differential expression levels. This study provides a relatively comprehensive investigation of the MADS-box family and anthocyanin biosynthetic genes in M. polytepala, and will facilitate our understanding of the regulatory mechanism underlying floral organization and color in basal angiosperms.

Floral appendages display an array of shapes and sizes. Among these organs, staminodes are morphologically diverse structures that have lost the ability to produce pollen, but in some instances, they produce fertile pollen grains. In the family Cactaceae staminodes are uncommon and range from simple linear to flat to spatulate structures, but studies describing their structural attributes are scanty. This study highlights the advantages of synchrotron radiation for sample preparation and as a research tool for plant biology. It describes the internal morphology of floral parts, particularly stamen, tepal, and staminode in the Plains Prickly Pear Cactus, Opuntia polyacantha, using synchrotron radiation micro-computed tomography (SR-μCT). It also shows the different anatomical features in reconstructed three-dimensional imaging of reproductive parts and discuss the advantages of the segmentation method to detect and characterize the configuration and intricate patterns of vascular networks and associated structures of tepal and androecial parts applying SR-μCT. This powerful technology led to substantial improvements in terms of resolution allowing a more comprehensive understanding of the anatomical organization underlying the vasculature of floral parts and inception of staminodes in O. polyacantha. Tepal and androecial parts have uniseriate epidermis enclosing loose mesophyll with mucilage secretory ducts, lumen, and scattered vascular bundles. Cryptic underlying structural attributes provide evidence of a vascularized pseudo-anther conjoint with tepals. The undefined contours of staminodial appendages (pseudo-anther) amalgamated to the tepals’ blurred boundaries suggest that staminodes originate from tepals, a developmental pattern supporting the fading border model of floral organ identity for angiosperms.

Saffron ( Crocus sativus L.) is an infertile perennial geophyte considered the most expensive spice in the world. Seasonal fluctuations and climate change have significant impact on the growth, development, and yield of saffron stigma, which is the economically valued part of plant. The stigma being part of the flower, the knowledge of phenotypic transition from dormant apical bud up to flowering is vital, yet, not explored properly. The complexity of flowering in C. sativus further accentuates by the lack of clear demarcation between flowering and non-flowering corms in terms of weight and sizes, as small corms are known to be vegetative only, while large ones produce flower. Therefore, chronological phenotyping on a weekly and quarterly basis of apical shoot and flowering primordia between June and October was carried out to understand the organogenesis sequentially. In large corms, the stamen was the first floral organ to initiate followed by the formation of tepal from the base of the stamen. The plants exhibited both synanthous and hysteranthous flowering. Untargeted metabolome analysis of dormant apical bud just before dormancy break from flowering buds from large corms as well as non-flowering buds from small corms identified the presence of many differentially accumulated metabolites including sphingosine and meglutol. Key metabolites such as phytosphingosine, 3-hydroxy-3-methyl glutaric acid, 3-acetamidopropanal, 6-hydroxykynurenic acid, d -serine, and 1- d -myo-inositol 3-phosphate were also detected having associated with isoprenoid biosynthesis, lignin pathway regulation, and carbohydrate metabolism that participates in flowering. The integration of morphological, histological, and metabolomic data offers a comprehensive view of the flowering process that can be utilised in future biotechnological interventions in C. sativus .