What Maintains Flower Colour Variation within Populations?

Haplotype-resolved genome assembly provides new insights into the genomic origin of purple colour in Prunus mume

Prunus mume, an important ornamental woody plant in the Rosaceae family, contains many interspecific hybridizations. Purple colour is a breeding trait of aesthetic value for P. mume, but little is known about the origin and genetic architecture of this trait. Here we address these issues by producing a haplotype-resolved genome from an interspecific hybrid cultivar of P. mume (M) and P. cerasifera 'Pissardii' (C), named P. mume 'Meiren', followed by a detailed molecular characterization. The final length of the diploid genome is 499.47 Mb, with 250.66 Mb of haplotype M (HM) and 248.79 Mb of haplotype C (HC). Approximately 95.42% (476.61 Mb) of the phased assembly is further anchored to 16 homologous chromosomes. Based on the genomic variation, we identify a 1.8 Mb large-fragmented inversion (INV) on chromosome 1b of HC, which co-segregates with purple colour traits of 'Meiren' inherited from its purple C parent 'Pissardii'. We find that a MYB transcription factor, PmmMYB10.5b, resides at the distal breakpoint of the INV, which displays consistent allele-specific expression (ASE). By directly binding to the promoter of anthocyanin synthetic alleles, PmmMYB10.5b serves as a co-activator to promote anthocyanin accumulation in 'Meiren' organs. Notably, the INV identified in 'Meiren' is generated from 'Pissardii' rather than P. cerasifera, which alters the promoter sequence of PmmMYB10.5b, activates its expression and results in the purple colour trait. Results from this study shed light on the evolutionary origin of purple colour in 'Meiren' and could potentially provide guidance on the genetic improvement of colour traits in ornamental woody plants.

Environment or Pollinators? Factors Shaping Breeding System and Spatial Variation in Nectar Properties and Pollination System in a Desert Species Fritillaria persica L. (Liliaceae)

Interaction with pollinators has been proposed as one of the most important factors shaping the diversity of flowering plants. Spatial variation in the directions of the selective pressure exerted by pollinators drives the evolution of adaptive differentiation. Across-population studies of flower traits and plant-pollinator interaction are therefore an important step to understanding the diverse selective pressures that drive floral evolution in zoogamous angiosperms. Here we combine observational data and field experiments to describe the assemblages of pollinators, breeding systems, and reward properties in studied populations of the Middle East geophyte, Fritillaria persica. Natural populations of this species include two floral color morphs with greenish or purple flowers; in both morphs, the nectaries of the outer whorl are covered by the tepals of the inner one. Our study documented geographical variation in the pollination system of two color morphs of F. persica. Visitors recorded in both populations were similar qualitatively; however, their contribution varied. Nectar sugar concentration and profile were generally constant in studied populations; we recorded differences only in nectar volume and concentration of amino acids. These results suggest that the observed variation in nectar production is likely to be a result of environmental factors rather than pollinator-mediated selection. In the context of reward, we also tested how uncovering the hidden nectar reward from outer tepals influences potential pollinators. Uncovering hidden reward did not change the time spent in one flower or inflorescence penetration; however, it increased the number of seeds produced. Nectar properties and the pollinator assemblages similarity suggest that in the context of pollination, F. persica represents a rather generalistic strategy, and observed differences may be caused by abiotic factors.

The consequences of flower colour polymorphism on the reproductive success of a neotropical deceptive orchid

Deceptive plants often exhibit elevated levels of polymorphism. The basis of the association between flower polymorphism and deceptive strategies, however, remains unclear. Epidendrum fulgens, a Neotropical deceptive orchid pollinated by butterflies, has an unexplored intrapopulation flower colour polymorphism. Here, we investigate the consequences of this polymorphism on its reproductive success. We performed field and common garden experiments, aiming to detect pollinator-mediated selection strength and direction over time, and test whether the presence of multiple colour morphs increases species' reproductive success. In the field, we monitored plant reproductive success and floral morphology on two populations over two flowering seasons and performed selection gradient analyses. In the common garden, we assembled plots of cultivated plants with same and different flower colour individuals (i.e., mono- and polymorphic plots), exposed them to pollinators and monitored their reproductive success. In both sites we also monitored the local pollinator community. In the field, colour morphs performed equally, but we found coherences between morphological differentiation and the direction of selection, which was very dynamic. In the common garden, mono- and polymorphic plots also performed equally, with highly variable reproductive success over time. We also found a highly diverse pollinator community. Our results suggest that flower polymorphism in E. fulgens is maintained by a combination of factors, including varying pollinator-mediated selection, assortative mating due to differential pollinator preferences and different phenotype heritability. Natural selection varied across time and space, indicating a dynamic interplay between pollinators and flower morphs.

Reproductive strategies of two color morphs of Paeonia delavayi

The diversity in floral coloration results from a complex reproductive system, which has evolved in response to multiple pollinators and is intricately linked to the development of pollination mechanisms. To investigate how floral trait variations influence reproduction in Paeonia delavayi, we conducted pollination experiments, observed insect visitation, measured floral traits, estimated petal and anther colors as perceived by pollinators and analyzed floral scent for two floral morphs (red and yellow) at two distinct sites. P. delavayi depended on insect pollinators for seed production. Multiple comparisons revealed that seed yields and seed sets under natural pollination were significantly higher than those under artificial pollination (homogamy and geitonogamy) and anemophilous pollination. However, there was no significant difference in seed yields(LWS, p = 0.487; XGLL, p = 0.702) and seed set (LWS, p = 0.077; XGLL, p = 0.251) between two floral morphs under natural pollination. Both morphs shared common pollinators, primarily honeybees, bumblebees, and syrphid flies. Major pollinators visited the yellow morph more frequently than the red morph, although there was no significant difference in the duration time of visits between the two morphs. Studies utilizing insect vision models, based on color reflection spectra, revealed that major pollinators could distinguish differences in petal and anther colors between the two morphs. However, there is variation in how pollinators perceive their flower colors. On the one hand, the yellow morphs contrast against the leaves background, enhancing their visual attractiveness to bees and flies. On the other hand, the red-flowered morph compensates for its visual disadvantage through olfactory cues, ensuring successful reproduction despite lower visual attractiveness. This study highlights the intricate interplay between visual and olfactory signals in plant-pollinator interactions, emphasizing their combined influence on reproductive outcomes.

Soil and climate contribute to maintenance of a flower color polymorphism

PREMISE

Floral pigments such as anthocyanins are well known to influence pollinator attraction, yet they also confer tolerance to abiotic stressors such as harsh soils, extreme temperatures, low precipitation, and UV radiation. In such cases, environmental variation in abiotic stressors over space or time could lead to the maintenance of flower color variation within species. Under this scenario, flower color in natural populations should covary with environmental stressors.

METHODS

Using a comparative approach, we tested whether abiotic variables predict flower color in Leptosiphon parviflorus, a species with pink and white flower color morphs. We conducted in-depth field studies to assess morph frequency, soil chemistry, and climate. We then employed community scientist-powered iNaturalist observations to examine patterns across even larger spatial scales.

RESULTS

Across 21 field sites, L. parviflorus had a higher frequency of pink morphs in sites with serpentine soil, higher average annual temperatures, and higher average climatic water deficit (a proxy for drought stress). iNaturalist observations supported this finding-the probability of flowers being pink is greater in locations with serpentine-derived soil, especially when the local average UV radiation and climatic water deficit are higher.

CONCLUSIONS

Spatial variation in abiotic stressors may contribute to the maintenance of flower color variation across the geographic range of L. parviflorus. Future studies will examine mechanisms by which flower color affects stress tolerance and will assess whether fitness trade-offs in contrasting habitats across the range are associated with flower color.

Genetic Mechanisms and Adaptive Benefits of Anthocyanin Red Stigmas in a Wind-Pollinated Tree

Anthocyanin accumulation in leaves or flowers mitigates photooxidation damage from reactive oxygen species (ROS) and functions in plant/animal interactions. Among the most conspicuously anthocyanin-accumulating tissues are stigmas, especially in wind-pollinated trees. In the walnut genus (Juglans), yellow stigmas are ancestral, but a few species have dark red stigmas. We have used a natural F1 hybrid resulting from crosses between yellow stigma and red stigma species to investigate the genetic basis of the red stigmas. We found that a Copia transposable element (TE) insertion in the ubiquitin-protein ligase gene MIEL1 suppresses its expression in stigmas through RNA-directed DNA methylation and has gone to fixation in red stigma species. A younger Gypsy TE insertion fully inhibits MIEL1 expression, but is not fixed, explaining the color segregation in hybrid populations. Based on reference genomes and whole-genome sequencing data representing 20 of the 22 species of Juglans, we traced the evolution of MIEL1, finding the insertions in all consistently red stigma species. Red stigmas had lower levels of ROS than yellow stigmas, and population genetic data reveal strong positive selection on the TE-bearing MIEL1 allele. In combination, these results suggest that anthocyanin-accumulating stigma tissues support pollen germination and growth by protecting cells from ROS.

When the sand blossoms: Phylogeny, trait evolution, and geography of speciation in Linanthus

PREMISE

Understanding how plants successfully diversified in novel environments is a central question in evolutionary biology. Linanthus occurs in arid areas of western North America and exhibits extensive floral trait variation, multiple color polymorphisms, differences in blooming time, and variation in life history strategies. We reconstructed the evolutionary history of this genus.

METHODS

We generated restriction-site associated (ddRAD) sequences for 180 individuals and target capture (TC) sequences for 63 individuals, with complete species sampling. Using maximum likelihood and pseudo-coalescent approaches, we inferred phylogenies of Linanthus and used them to model the evolution of phenotypic traits and investigate the genus's geographic speciation history.

RESULTS

Relationships are consistent and well supported with both ddRAD and TC data. Most species are monophyletic despite extensive local sympatry and range overlap, suggesting strong isolating barriers. The non-monophyly of the night-blooming and perennial species may be due to rapid speciation or cryptic diversity. Perenniality likely evolved from annuality, a rare shift in angiosperms. Night-blooming evolved three times independently. Flower color polymorphism is an evolutionarily labile trait that is likely ancestral. No single geographic mode of speciation characterizes this diversification, but most species overlap in range, which suggests that they evolved in parapatry.

CONCLUSIONS

Our results illustrate the complexity of phylogenetic inference for recent radiations, even with multiple sources of genomic data and extensive sampling. This analysis provides a foundation for understanding aridity adaptations, such as evolution of flower color polymorphisms, night-blooming, and perenniality, as well as speciation mechanisms.

Function of Anthocyanin and Chlorophyll Metabolic Pathways in the Floral Sepals Color Formation in Different Hydrangea Cultivars

Hydrangea (Hydrangea macrophylla) is distinguished by having sepals instead of real petals, a trait that facilitates color diversity. Floral color is largely predetermined by structural genes linked to anthocyanin production, but the genetic factors determining floral hue in this non-model plant remain unclear. Anthocyanin metabolites, transcriptome, and the CIEL*a*b* hue system were employed to elucidate the biochemical and molecular mechanisms of floral color formation in three hydrangea cultivars: 'DB' (deep blue), 'LB' (light blue), and 'GB' (green blue). UPLC-MS/MS identified 47 metabolites, with delphinidin, cyanidin, malvidin, petunidin, pelargonidin, and peonidin being prominent. Delphinidins were 90% of the primary component in 'DB'. The dataset identifies 51 and 31 DEGs associated with anthocyanin, flavonoid, and chlorophyll biosynthesis, with CHS, CHI, F3H, F3'5'H, DFR, ANS, BZ1, and 3AT displaying the highest expression in 'DB'. Notably, DFR (cluster-46471.3) exhibits high expression in 'DB' while being down-regulated in 'LB' and 'GB', correlating with higher anthocyanin levels in floral pigmentation. Comparative analyses of 'LB' vs. 'DB', 'DB' vs. 'GB', and 'LB' vs. 'GB' revealed 460, 490, and 444 differentially expressed TFs, respectively. WRKY, ERF, bHLH, NAC, and AP2/ERF showed the highest expression in 'DB', aligning with the color formation and key anthocyanin biosynthesis-related gene expression. The findings reveal the molecular mechanisms behind floral pigmentation variations and lay the groundwork for future hydrangea breeding programs.

The roles of florivory and herbivory in maintaining intra-population flower colour variation in Anemone coronaria

Most flowering plants are colour monomorphic, while within-population flower colour variation is rare. Multiple selection agents on flower colour, each favouring a different colour morph, may drive such uncommon polymorphisms. We tested the role of biotic antagonistic interactions in maintaining flower colour variation in Anemone coronaria (Ranunculaceae), in colour-polymorphic populations comprised of red, purple, and white flowers. We estimated the extent of leaf herbivory and petal florivory in each flower colour morph in three populations over two flowering seasons. We categorized types of damage to four groups of herbivores and estimated the plant maternal fitness. We tested pollinator response to different levels (0-30%) of simulated florivory in experimental flower arrays. Leaf and petal damage did not differ between white- and purple-flowering plants. Red-flowering plants had higher leaf damage than white-flowering plants and higher petal damage than purple-flowering plants. Nevertheless, all colour morphs had similar fitness. Red flowers exhibited more petal scratches (attributed to glaphyrid beetles), but fewer petal bites (attributed to caterpillars or grasshoppers), than white and purple flowers. Experimentally induced florivory did not reduce visits by potential pollinators in any colour morph. Glaphyrid beetles are the major pollinators of red anemone flowers, suggesting that their service to red flowers as mutualists (pollinators) should be weighed against their disservice as antagonists (florivores). A balance between pollination service and petal scratch damage of red flowers, both mediated by Glaphyird beetles, may equalize fitness between the red and the purple/white colour morphs, contributing to colour polymorphism.

Pollinator response to yellow UV-patterned versus white UV-patternless flower dimorphism in Anemone palmata

Flower colour polymorphisms are uncommon but widespread among angiosperms and can be maintained by a variety of balancing selection mechanisms. Anemone palmata is mostly yellow-flowered, but white-flowered plants coexist in some populations. We analysed the distribution of colour morphs of A. palmata across its range. We also characterised their colours and compared their vegetative and sexual reproductive traits, pollinator attention and fitness. The range of A. palmata is limited to the Western Mediterranean, while white-flowered plants are restricted to Portugal and SW Spain, where they occur at low proportions. Yellow flowers have a characteristic UV pattern, with a UV-absorbing centre and UV-reflecting periphery, which is absent in the white morph. Colour features of both morphs were highly delineated, making it easy for pollinators to distinguish them. Both morphs were protogynous, with the same duration of sexual stages, and the main floral traits related to pollinator attraction, apart from flower colour, were similar. Hymenoptera and Diptera were the main pollinators, showing preference for the yellow morph, clear partitioning of pollinator groups between the two colour morphs and a marked constancy to flower colour during foraging. Both morphs combined clonal propagation with sexual reproduction, but sexual reproductive potential was lower in white-flowered plants. Finally, female fitness was higher in the yellow morph. Pollinator partitioning and colour constancy could maintain this polymorphism, despite the lower visitation rate and fitness of white-flowered plants, which could facilitate their clonal propagation.

Population structure and natural selection across a flower color polymorphism in the desert plant Encelia farinosa

PREMISE

Clines-or the geographic sorting of phenotypes across continual space-provide an opportunity to understand the interaction of dispersal, selection, and history in structuring polymorphisms.

METHODS

In this study, we combine field-sampling, genetics, climatic analyses, and machine learning to understand a flower color polymorphism in the wide-ranging desert annual Encelia farinosa.

RESULTS

We find evidence for replicated transitions in disk floret color from brown to yellow across spatial scales, with the most prominent cline stretching ~100 km from southwestern United States into México. Because population structure across the cline is minimal, selection is more likely than drift to have an important role in determining cline width.

CONCLUSIONS

Given that the cline aligns with a climatic transition but there is no evidence for pollinator preference for flower color, we hypothesize that floret color likely varies as a function of climatic conditions.

You can't always get what you want from pollinators

This article is a Commentary on Duncan et al. (2024), 244: 307–317.

Transcriptome Analysis Revealed the Anabolic Regulation of Chlorophyll and Carotenoids in Curcuma alismatifolia Bracts

Curcuma alismatifolia is an attractive ornamental plant in the ginger family. Its bracts come in a variety of colors and are commonly used as cut flowers, potted plants, and landscaping. To investigate the regulation of bract pigmentation in C. alismatifolia, we examined the pigment levels of chlorophyll and carotenoids in the pure color part (PC) and variegated part (VA) of three C. alismatifolia varieties, i.e., "Siam TM Sitrone," "Chiang Mai Pink," and "Snow White." To mine the color mechanisms of the pure color and variegated parts of the bract, we conducted RNA-seq analysis on C. alismatifolia. We identified a total of 89,975 unigenes, and there were 3584 differentially expressed genes identified post-screening. Furthermore, 1858 DEGs were annotated in the GO database and 681 in the KEGG database. We pinpointed key genes responsible for the diverse bract colors in C. alismatifolia, including ZEP for carotenoid synthesis and GAGA2 in the chlorophyll synthesis pathway. This study provides valuable insights into understanding the pigmentation mechanism of bracts in C. alismatifolia and the breeding process.

Experimental evolution suggests rapid assembly of the 'selfing syndrome' from standing variation in Mimulus guttatus

Ecological and evolutionary changes are likely to occur rapidly when outcrossing populations experience pollinator loss. However, the number and identify of plant traits that will respond to this form of selection, as well as the overall predictability of evolutionary responses, remain unclear. We experimentally evolved 20 large replicate populations of Mimulus guttatus for 10 generations under three treatments: pure outcrossing, mixed mating (10% outcrossing) and pure selfing. These populations were founded from the same genetically diverse and outcrossing natural population. After 10 generations, all measured traits evolved with flower size, phenology, and reproductive traits diverging consistently among mating system treatments. Autogamy increased dramatically in the selfing treatment, but the magnitude of adaptation only becomes clear once inbreeding depression is factored out. Selfing treatment plants evolved reduced stigma-anther separation, and also exhibited declines in flower size and per-flower reproductive capacity. Flower size also declined in selfing populations but this was driven mainly by inbreeding depression and cannot be attributed to adaptation towards the selfing syndrome. Generally, the mixed mating populations evolved trait values intermediate to the fully selfing and outcrossing populations. Overall, our experimental treatments reiterated differences that have been documented in interspecific comparisons between selfing and outcrossing species pairs. Given that such contrasts involve species separated by thousands or even millions of generations, it is noteworthy that large evolutionary responses were obtained from genetic variation segregating within a single natural population.

QTL analysis of divergent floral morphology traits between Gilia yorkii and G. capitata

Speciation is a complex process typically accompanied by significant genetic and morphological differences between sister populations. In plants, divergent floral morphologies and pollinator differences can result in reproductive isolation between populations. Here, we explore floral trait differences between two recently diverged species, Gilia yorkii and G. capitata. The distributions of floral traits in parental, F1, and F2 populations are compared, and groups of correlated traits are identified. We describe the genetic architecture of floral traits through a quantitative trait locus analysis using an F2 population of 187 individuals. While all identified quantitative trait locus were of moderate (10-25%) effect, interestingly, most quantitative trait locus intervals were non-overlapping, suggesting that, in general, traits do not share a common genetic basis. Our results provide a framework for future identification of genes involved in the evolution of floral morphology.

Genetic factors explaining anthocyanin pigmentation differences

BACKGROUND

Anthocyanins are important contributors to coloration across a wide phylogenetic range of plants. Biological functions of anthocyanins span from reproduction to protection against biotic and abiotic stressors. Owing to a clearly visible phenotype of mutants, the anthocyanin biosynthesis and its sophisticated regulation have been studied in numerous plant species. Genes encoding the anthocyanin biosynthesis enzymes are regulated by a transcription factor complex comprising MYB, bHLH and WD40 proteins.

RESULTS

A systematic comparison of anthocyanin-pigmented vs. non-pigmented varieties was performed within numerous plant species covering the taxonomic diversity of flowering plants. The literature was screened for cases in which genetic factors causing anthocyanin loss were reported. Additionally, transcriptomic data sets from four previous studies were reanalyzed to determine the genes possibly responsible for color variation based on their expression pattern. The contribution of different structural and regulatory genes to the intraspecific pigmentation differences was quantified. Differences concerning transcription factors are by far the most frequent explanation for pigmentation differences observed between two varieties of the same species. Among the transcription factors in the analyzed cases, MYB genes are significantly more prone to account for pigmentation differences compared to bHLH or WD40 genes. Among the structural genes, DFR genes are most often associated with anthocyanin loss.

CONCLUSIONS

These findings support previous assumptions about the susceptibility of transcriptional regulation to evolutionary changes and its importance for the evolution of novel coloration phenotypes. Our findings underline the particular significance of MYBs and their apparent prevalent role in the specificity of the MBW complex.

The road less taken: Dihydroflavonol 4-reductase inactivation and delphinidin anthocyanin loss underpins a natural intraspecific flower colour variation

Visual cues are of critical importance for the attraction of animal pollinators, however, little is known about the molecular mechanisms underpinning intraspecific floral colour variation. Here, we combined comparative spectral analysis, targeted metabolite profiling, multi-tissue transcriptomics, differential gene expression, sequence analysis and functional analysis to investigate a bee-pollinated orchid species, Glossodia major with common purple- and infrequent white-flowered morphs. We found uncommon and previously unreported delphinidin-based anthocyanins responsible for the conspicuous and pollinator-perceivable colour of the purple morph and three genetic changes underpinning the loss of colour in the white morph - (1) a loss-of-function (LOF; frameshift) mutation affecting dihydroflavonol 4-reductase (DFR1) coding sequence due to a unique 4-bp insertion, (2) specific downregulation of functional DFR1 expression and (3) the unexpected discovery of chimeric Gypsy transposable element (TE)-gene (DFR) transcripts with potential consequences to the genomic stability and post-transcriptional or epigenetic regulation of DFR. This is one of few known cases where regulatory changes and LOF mutation in an anthocyanin structural gene, rather than transcription factors, are important. Furthermore, if TEs prove to be a frequent source of mutation, the interplay between environmental stress-induced TE evolution and pollinator-mediated selection for adaptive colour variation may be an overlooked mechanism maintaining floral colour polymorphism in nature.

Salvia guidongensis sp. nov.: unraveling a critical evolutionary link in East Asian Salvia from Central China integrating morphology, phylogeny, and plastid genomics

Introduction

Salvia L., representing the largest genus within the mint family, is noted for its global distribution of approximately 1000 species, with East Asia, and particularly China, recognized as a critical center of diversity for the genus.

Methods

Our research was conducted through extensive fieldwork in Guidong County, Hunan Province, China, where we identified a previously undescribed species of Salvia. The identification process involved detailed morphological observations, phylogenetic analyses, and plastid genomics.

Results

The newly discovered species, Salvia guidongensis, exhibits unique characteristics not commonly observed in the East Asian lineage of Salvia, including dual floral colors within natural populations-either pale purple or pale yellow. Morphologically, while it shares similarities with members of sect. Glutinaria, S. guidongensis is distinct in its floral morphology, stature, and specific foliar traits. Phylogenetic analysis places S. guidongensis in a unique clade within the East Asian lineage of Salvia, suggesting it may serve as an important evolutionary link. Additionally, we explored the plastome features of S. guidongensis, comparing them with those of closely related species.

Discussion

The discovery of S. guidongensis not only entriches the taxonomic tapestry of Salvia but also provides critical insights into the biogeography and evolutionary pathways of the genus in East Asia. By integrating morphological and molecular data, we validate the novel status of S. guidongensis and highlight its significance in bridging taxonomic and evolutionary gaps within Sect. Glutinaria of Salvia.

Genetic structure, UV-vision, wing coloration and size coincide with colour polymorphism in Fabriciana adippe butterflies

Colour polymorphisms have long served as model systems in evolutionary studies and continue to inform about processes involved in the origin and dynamics of biodiversity. Modern sequencing tools allow for evaluating whether phenotypic differences between morphs reflect genetic differentiation rather than developmental plasticity, and for investigating whether polymorphisms represent intermediate stages of diversification towards speciation. We investigated phenotypic and genetic differentiation between two colour morphs of the butterfly Fabriciana adippe using a combination of ddRAD-sequencing and comparisons of body size, colour patterns and optical properties of bright wing spots. The silvery-spotted adippe form had larger and darker wings and reflected UV light, while the yellow cleodoxa form displayed more green scales and reflected very little UV, showcasing that they constitute distinct and alternative integrated phenotypes. Genomic analyses revealed genetic structuring according to source population, and to colour morph, suggesting that the phenotypic differentiation reflects evolutionary modifications. We report 17 outlier loci associated with colour morph, including ultraviolet-sensitive visual pigment (UVRh1), which is associated with intraspecific communication and mate choice in butterflies. Together with the demonstration that the wings of the adippe (but essentially not the cleodoxa) morph reflect UV light, that UV reflectance is higher in females than males and that morphs differ in wing size, this suggests that these colour morphs might represent genetically integrated phenotypes, possibly adapted to different microhabitats. We propose that non-random mating might contribute to the differentiation and maintenance of the polymorphism.

Intraspecific floral colour variation in three Pedicularis species

Flower constancy describes the phenomenon that pollinators tend to successively visit flowers of a single species during foraging, reducing reproductive interference in natural communities. The extent of flower constancy is largely determined by the floral traits of co-flowering species. Both higher inter-specific and lower intraspecific differences of floral traits should contribute to a higher level of flower constancy. However, previous studies mainly focused on interspecific difference, and the intraspecific variation (consistency) of floral traits received much less attention. We hypothesise that selection may favour lower intraspecific floral trait variation in communities composed of multiple co-flowering congeners. We investigated the floral colour variation of three focal Pedicularis species that share pollinators in 19 communities composed of either single or multiple Pedicularis species. Colour was quantified using image-based colour analysis as perceived by pollinators. We found that most of the intrapopulation floral colour variation was below the colour discrimination threshold of bumblebees, implying strongly constrained by the visual selection by pollinators. Contrary to the hypothesis, there is no significant difference in intraspecific floral colour variation between different community contexts. It may be due to the relatively large interspecific floral colour differences of most co-flowering species. The influence of community context on intraspecific variation may be reflected in floral traits other than colours.

Flower color polymorphism of a wild Iris on the Qinghai-Tibet plateau

BACKGROUND

Flower color plays a crucial role in attracting pollinators and facilitating environmental adaptation. Investigating the causes of flower color polymorphism and understanding their potential effects on both ecology and genetics can enhance our understanding of flower color polymorphism in wild plant.

RESULTS

In this study, we examined the differences of potential male and female fitness between purple- and yellow- flower individuals in Iris potaninii on the Qinghai-Tibet Plateau, and screened key genes and positively selective genes involved in flower color change. Our results showed that yellow flower exhibited a higher pollen-to-ovule ratio. Yellow flowers were derived from purple flowers due to the loss of anthocyanins, and F3H could be an essential gene affecting flower color variation though expression regulation and sequence polymorphism in this species. Furthermore, our findings suggest that genes positively selected in yellow-flowered I. potaninii might be involved in nucleotide excision repair and plant-pathogen interactions.

CONCLUSIONS

These results suggest that F3H induces the flower color variation of Iris potaninii, and the subsequent ecological and additive positive selection on yellow flowers may further enhance plant adaptations to alpine environments.

Genetics of yellow-orange color variation in a pair of sympatric sulphur butterflies

Continuous color polymorphisms can serve as a tractable model for the genetic and developmental architecture of traits. Here we investigated continuous color variation in Colias eurytheme and Colias philodice, two species of sulphur butterflies that hybridize in sympatry. Using quantitative trait locus (QTL) analysis and high-throughput color quantification, we found two interacting large-effect loci affecting orange-to-yellow chromaticity. Knockouts of red Malpighian tubules (red), likely involved in endosomal maturation, result in depigmented wing scales. Additionally, the transcription factor bric-a-brac can act as a modulator of orange pigmentation. We also describe the QTL architecture of other continuously varying traits, together supporting a large-X effect model where the genetic control of species-defining traits is enriched on sex chromosomes. This study sheds light on the range of possible genetic architectures that can underpin a continuously varying trait and illustrates the power of using automated measurement to score phenotypes that are not always conspicuous to the human eye.

Transcriptome and metabolome analysis reveals the effect of flavonoids on flower color variation in Dendrobium nobile Lindl

Introduction

Dendrobium nobile L. is a rare orchid plant with high medicinal and ornamentalvalue, and extremely few genetic species resources are remaining in nature. In the normal purple flower population, a type of population material with a white flower variation phenotype has been discovered, and through pigment component determination, flavonoids were preliminarily found to be the main reason for the variation.

Methods

This study mainly explored the different genes and metabolites at different flowering stages and analysed the flower color variation mechanism through transcriptome- and flavonoid-targeted metabolomics. The experimental materials consisted of two different flower color phenotypes, purple flower (PF) and white flower (WF), observed during three different periods.

Results and discussion

The results identified 1382, 2421 and 989 differentially expressed genes (DEGs) in the white flower variety compared with the purple flower variety at S1 (bud stage), S2 (chromogenic stage) and S3 (flowering stage), respectively. Among these, 27 genes enriched in the ko00941, ko00942, ko00943 and ko00944 pathways were screened as potential functional genes affecting flavonoid synthesis and flower color. Further analysis revealed that 15 genes are potential functional genes that lead to flavonoid changes and flower color variations. The metabolomics results at S3 found 129 differentially accumulated metabolites (DAMs), which included 8 anthocyanin metabolites, all of which (with the exception of delphinidin-3-o-(2'''-o-malonyl) sophoroside-5-o-glucoside) were found at lower amounts in the WF variety compared with the PF variety, indicating that a decrease in the anthocyanin content was the main reason for the inability to form purple flowers. Therefore, the changes in 19 flavone and 62 flavonol metabolites were considered the main reasons for the formation of white flowers. In this study, valuable materials responsible for flower color variation in D. nobile were identified and further analyzed the main pathways and potential genes affecting changes in flavonoids and the flower color. This study provides a material basis and theoretical support for the hybridization and molecular-assisted breeding of D. nobile.

The evolution of flower colour

Flowers are the most commonly seen colourful elements of the natural world, and in this primer we explain the evolution of their spectacular range of colours. To understand flower colour, we first explain what colour is and how a flower can have different colours in the eyes of different observers. We briefly introduce the molecular and biochemical basis of flower colour, which is primarily based on well-characterised pigment synthesis pathways. We then consider the evolution of flower colour over four timescales - its origin and deep evolution, its macroevolution, its microevolution and finally, the recent effects of human behaviour on flower colour and its evolution. Because flower colour is so evolutionarily labile, and at the same time so striking to the human eye, it is an exciting subject for current and future research efforts.

Purple Rehmannnia : investigation of the activation of R2R3-MYB transcription factors involved in anthocyanin biosynthesis

Engineering anthocyanin biosynthesis in herbs could provide health-promoting foods for improving human health. Rehmannia glutinosa is a popular medicinal herb in Asia, and was a health food for the emperors of the Han Dynasty (59 B.C.). In this study, we revealed the differences in anthocyanin composition and content between three Rehmannia species. On the 250, 235 and 206 identified MYBs in the respective species, six could regulate anthocyanin biosynthesis by activating the ANTHOCYANIDIN SYNTHASE (ANS) gene expression. Permanent overexpression of the Rehmannia MYB genes in tobacco strongly promoted anthocyanin content and expression levels of NtANS and other genes. A red appearance of leaves and tubers/roots was observed, and the total anthocyanin content and the cyanidin-3-O-glucoside content were significantly higher in the lines overexpressing RgMYB41, RgMYB42 and RgMYB43 from R. glutinosa,as well as RcMYB1 and RcMYB3 in R. chingii and RhMYB1 from R. henryi plants. Knocking out of RcMYB3 by CRISPR/Cas9 gene editing resulted in the discoloration of the R. chingii corolla lobes, and decreased the content of anthocyanin. R. glutinosa overexpressing RcMYB3 displayed a distinct purple color in the whole plants, and the antioxidant activity of the transgenic plants was significantly enhanced compared to WT. These results indicate that Rehmannia MYBs can be used to engineer anthocyanin biosynthesis in herbs to improve their additional value, such as increased antioxidant contents. This article is protected by copyright. All rights reserved.

Floral colour variation of Nicotiana glauca in native and non-native ranges: Testing the role of pollinators' perception and abiotic factors

Invasive plants displaying disparate pollination environments and abiotic conditions in native and non-native ranges provide ideal systems to test the role of different ecological factors driving flower colour variation. We quantified corolla reflectance of the ornithophilous South American Nicotiana glauca in native populations, where plants are pollinated by hummingbirds, and in populations from two invaded regions: South Africa, where plants are pollinated by sunbirds, and the Balearic island of Mallorca, where plants reproduce by selfing. Using visual modelling we examined how corolla reflectance could be perceived by floral visitors present in each region. Through Mantel tests we assessed a possible association between flower colour and different abiotic factors. Corolla reflectance variation (mainly along medium to long wavelengths, i.e. human green-yellow to red colours) was greater among studied regions than within them. Flower colour was more similar between South America and South Africa, which share birds as pollinators. Within invaded regions, corolla reflectance variation was lower in South Africa, where populations could not be distinguished from each other by sunbirds, than in Spain, where populations could be distinguished from each other by their occasional visitors. Differences in corolla colour among populations were partially associated with differences in temperature. Our findings suggest that shifts in flower colour of N. glauca across native and invaded ranges could be shaped by changes in both pollination environment and climatic factors. This is the first study on plant invasions considering visual perception of different pollinators and abiotic drivers of flower colour variation.

Variation in scent amount but not in composition correlates with pollinator visits within populations of deceptive Arum maculatum L. (Araceae)

Floral scent is vital for pollinator attraction and varies among and within plant species. However, little is known about how inter-individual variation in floral scent affects the abundance and composition of floral visitor assemblages within populations. Moreover, for deceptive plants it is predicted that intra-population variation in scent can be maintained by negative frequency-dependent selection, but empirical evidence is still lacking. To investigate the ecological and evolutionary relations between inter-individual scent variation (i.e., total emission and composition) and floral visitors in deceptive plants, we studied floral scent, visitor assemblages, and fruit set in two populations of fly-pollinated (Psychodidae, Sphaeroceridae; Diptera) and deceptive Arum maculatum from Austria (JOS) and northern Italy (DAO). By correlating individual data on floral scent and visitor assemblages, we show that inter-individual variation in floral scent partly explains variation in visitor assemblages. The quantity of floral scent emitted per individual correlated positively with visitor abundance in both populations but explained visitor composition only in DAO, where strongly scented inflorescences attracted more sphaerocerid flies. However, in each population, the composition of floral scent did not correlate with the composition of floral visitors. There was also no evidence of negative frequency-dependent selection on floral scent. Instead, in JOS, more frequent scent phenotypes attracted more pollinators and were more likely to set an infructescence than rarer ones. Our results show that floral scent, despite being key in pollinator attraction in A. maculatum, only partly explains variation in pollinator abundance and composition. Overall, this study is the first to shed light on the importance of inter-individual variation in floral scent in explaining floral visitor assemblages at the population level in a deceptive plant species.

Pollinators exert selection on floral traits in a pollen-limited, narrowly endemic spring ephemeral

PREMISE

Floral traits are frequently under pollinator-mediated selection, especially in taxa subject to strong pollen-limitation, such as those reliant on pollinators. However, antagonists can be agents of selection on floral traits as well. The causes of selection acting on spring ephemerals are understudied though these species can experience particularly strong pollen-limitation. I examined pollinator- and antagonist-mediated selection in a narrowly endemic spring ephemeral, Trillium discolor.

METHODS

I measured pollen limitation in T. discolor across two years and evaluated its breeding system. I compared selection on floral traits (display height, petal size, petal color, flowering time) between open-pollinated, and pollen-supplemented plants to measure the strength and mode of pollinator-mediated selection. I assessed whether natural levels of antagonism impacted selection on floral traits.

RESULTS

Trillium discolor was self-incompatible and experienced pollen limitation in both years of the study. Pollinators exerted negative disruptive selection on display height and petals size. In one year, pollinator-mediated selection favored lighter petals but in the second year pollinators favored darker petals. Antagonist damage did not alter selection on floral traits.

CONCLUSIONS

Results demonstrate that pollinators mediate the strength and mode of selection on floral traits in T. discolor. Interannual variation in the strength, mode, and direction of pollinator-mediated selection on floral traits could be important for maintaining of floral diversity in this system. Observed levels of antagonism were weak agents of selection on floral traits.

Morphological Characteristics and Comparative Chloroplast Genome Analyses between Red and White Flower Phenotypes of Pyracantha fortuneana (Maxim.) Li (Rosaceae), with Implications for Taxonomy and Phylogeny

Pyracantha fortuneana (Maxim.) Li (Rosaceae), commonly known as Chinese firethorn, is an evergreen shrub with high nutritional, medicinal, and horticultural importance. This species typically has white flowers, but a rare red flower phenotype has been found in very few wild populations in western Hubei, China, showing great ornamental potential. In this study, the complete chloroplast genome of the red flower phenotype of P. fortuneana was reported for the first time, using high-throughput sequencing technology. The complete chloroplast genome was 160,361 bp in length and showed a typical quadripartite structure with a pair of inverted repeat (IR) regions (26,350 bp) separated by a large single-copy (LSC) region (88,316 bp) and a small single-copy (SSC) region (19,345 bp). A total of 131 functional genes were annotated in this chloroplast genome, including 86 protein-coding genes (PCGs), eight rRNA genes, and 37 tRNA genes. Comparative chloroplast genome analyses revealed that high genome similarity existed not only between red and white flower phenotypes of P. fortuneana, but also among Pyracantha species. No evidence for positive selection was found in any PCG, suggesting the evolutionary conservation of Pyracantha chloroplast genomes. Furthermore, four mutational hotspots (trnG-trnR-atpA, psbZ-trnG-trnfM-rps14, ycf3-trnS-rps4, and ndhF-rpl32) with π > 0.004 were identified as potential molecular markers for Pyracantha species. Phylogenomic analysis strongly supported that the red flower phenotype of P. fortuneana was nested within the common white flower phenotype. Based on both morphological and molecular evidence, we suggest that the red flower phenotype of P. fortuneana could be considered as a new forma. Overall, the availability of these genetic resources will not only offer valuable information for further studies on molecular taxonomy, phylogeny, and population genetics of Pyracantha species but also could be used as potential genetic resources for Chinese firethorn breeding.

Comparative Transcriptome Analysis Unveils the Molecular Mechanism Underlying Sepal Colour Changes under Acidic pH Substratum in Hydrangea macrophylla

The hydrangea (Hydrangea macrophylla (Thunb). Ser.), an ornamental plant, has good marketing potential and is known for its capacity to change the colour of its inflorescence depending on the pH of the cultivation media. The molecular mechanisms causing these changes are still uncertain. In the present study, transcriptome and targeted metabolic profiling were used to identify molecular changes in the RNAome of hydrangea plants cultured at two different pH levels. De novo assembly yielded 186,477 unigenes. Transcriptomic datasets provided a comprehensive and systemic overview of the dynamic networks of the gene expression underlying flower colour formation in hydrangeas. Weighted analyses of gene co-expression network identified candidate genes and hub genes from the modules linked closely to the hyper accumulation of Al³⁺ during different stages of flower development. F3'5'H, ANS, FLS, CHS, UA3GT, CHI, DFR, and F3H were enhanced significantly in the modules. In addition, MYB, bHLH, PAL6, PAL9, and WD40 were identified as hub genes. Thus, a hypothesis elucidating the colour change in the flowers of Al³⁺-treated plants was established. This study identified many potential key regulators of flower pigmentation, providing novel insights into the molecular networks in hydrangea flowers.

Composition of major quinochalcone hydroxysafflor yellow A and anhydrosafflor yellow B is associated with colour of safflower (Carthamus tinctorius) during colour-transition but not with overall antioxidant capacity: A study on 144 cultivars

Yellow pigments in the water-extract of safflower (Carthamus tinctorius L.) belong to quinochalcone flavonoid family and are widely used as food colourants. The aim of the study was to characterize the main quinochalcone compounds in safflower water-extract during blooming period when floret changed colour. Mass-spectrometry results showed that hydroxysafflor yellow A (HSYA) and anhydrosafflor yellow B (AHSYB) were the most abundant. Based on 370 florets samples collected from 144 cultivars, the contents of HSYA and AHSYB were determined, which showed that only AHSYB content had relatively strong positive association with colour indexes. The ratio of HSYA/AHSYB and visual colour exhibited certain patterns: yellow = 2, orange = 3-4, red = more dispersed, mostly falling 5-6. Most of the florets had HSYA increased first and decreased, while AHSYB decreased all the time when floret changed colour as yellow → orange → red. Regardless of the composition of HSYA/AHSYB in florets, the antioxidant capacities of safflower petal water-extracts were the same.

Mechanisms of flower coloring and eco-evolutionary implications of massive blooming events in the Atacama Desert

The Atacama Desert, one of the driest places on earth, holds a rich biodiversity that becomes most appreciable in years when unusual rainfall accumulation triggers a phenomenon of explosive development of ephemeral herbaceous and woody desert species known as “desierto florido” or “blooming desert.” Despite the scientific importance of this unique phenomenon only few studies have addressed the mechanisms of flower phenotypic divergence under the fluctuating environment provided by this recurrent event. We investigated the mechanisms of floral color diversity in Cistanthe longiscapa (Montiaceae), a dominant species across the ephemeral blooming landscape of Atacama Desert. Our analyses show that the variation in colors of C. longiscapa flowers result from petals containing betalain pigments with different absorption spectra. The different pigment composition of petals causes flower color differences in the visible and ultraviolet (UV) range of the spectrum. Through color vision models we show that C. longiscapa flowers are highly polymorphic in their color appearance for insect pollinators. Our results highlight the variable nature in flower color of C. longiscapa varieties blooming simultaneously in a geographical restricted area. Given the importance of color in attracting floral visitors, the observed color variability could contribute to increased cross pollination in extreme desert conditions, while accounting for complex and fluctuating histories of plant-pollinator interactions.

Are some species ‘robust’ to exploitation? Explaining persistence in deceptive relationships

Animals and plants trick others in an extraordinary diversity of ways to gain fitness benefits. Mimicry and deception can, for example, lure prey, reduce the costs of parental care or aid in pollination–in ways that impose fitness costs on the exploited party. The evolutionary maintenance of such asymmetric relationships often relies on these costs being mitigated through counter-adaptations, low encounter rates, or indirect fitness benefits. However, these mechanisms do not always explain the evolutionary persistence of some classic deceptive interactions.

Sexually deceptive pollination (in which plants trick male pollinators into mating with their flowers) has evolved multiple times independently, mainly in the southern hemisphere and especially in Australasia and Central and South America. This trickery imposes considerable costs on the males: they miss out on mating opportunities, and in some cases, waste their limited sperm on the flower. These relationships appear stable, yet in some cases there is little evidence suggesting that their persistence relies on counter-adaptations, low encounter rates, or indirect fitness benefits. So, how might these relationships persist?

Here, we introduce and explore an additional hypothesis from systems biology: that some species are robust to exploitation. Robustness arises from a species’ innate traits and means they are robust against costs of exploitation. This allows species to persist where a population without those traits would not, making them ideal candidates for exploitation. We propose that this mechanism may help inform new research approaches and provide insight into how exploited species might persist.

How Much Pigment Should Flowers Have? Flowers With Moderate Pigmentation Have Highest Color Contrast

Floral pigments are a core component of flower colors, but how much pigment a flower should have to yield a strong visual signal to pollinators is unknown. Using an optical model and taking white, blue, yellow and red flowers as case studies, I investigate how the amount of pigment determines a flower’s color contrast. Modeled reflectance spectra are interpreted using established insect color vision models. Contrast as a function of the amount of pigment shows a pattern of diminishing return. Low pigment amounts yield pale colors, intermediate amounts yield high contrast, and extreme amounts of pigment do not further increase, and sometimes even decrease, a flower’s color contrast. An intermediate amount of floral pigment thus yields the highest visibility, a finding that is corroborated by previous behavioral experiments on bees. The implications for studies on plant-pollinator signaling, intraspecific flower color variation and the costs of flower color are discussed.

Flower Color Evolution and the Evidence of Pollinator-Mediated Selection

The evolution of floral traits in animal-pollinated plants involves the interaction between flowers as signal senders and pollinators as signal receivers. Flower colors are very diverse, effect pollinator attraction and flower foraging behavior, and are hypothesized to be shaped through pollinator-mediated selection. However, most of our current understanding of flower color evolution arises from variation between discrete color morphs and completed color shifts accompanying pollinator shifts, while evidence for pollinator-mediated selection on continuous variation in flower colors within populations is still scarce. In this review, we summarize experiments quantifying selection on continuous flower color variation in natural plant populations in the context of pollinator interactions. We found that evidence for significant pollinator-mediated selection is surprisingly limited among existing studies. We propose several possible explanations related to the complexity in the interaction between the colors of flowers and the sensory and cognitive abilities of pollinators as well as pollinator behavioral responses, on the one hand, and the distribution of variation in color phenotypes and fitness, on the other hand. We emphasize currently persisting weaknesses in experimental procedures, and provide some suggestions for how to improve methodology. In conclusion, we encourage future research to bring together plant and animal scientists to jointly forward our understanding of the mechanisms and circumstances of pollinator-mediated selection on flower color.

Geographical Variation in Flower Color in the Grassland Daisy Gerbera aurantiaca: Testing for Associations With Pollinators and Abiotic Factors

Geographical variation in flower color of a plant species may reflect the outcome of selection by pollinators or may reflect abiotic factors such as soil chemistry or neutral processes such as genetic drift. Here we document striking geographical structure in the color of capitula of the endemic South African grassland daisy Gerbera aurantiaca and ask which of these competing explanations best explains this pattern. The color of capitula ranges from predominantly red in the southwest to yellow in the center, with some northern populations showing within-population polymorphism. Hopliine scarab beetles were the most abundant flower visitors in all populations, apart from a yellow-flowered one where honeybees were frequent. In a mixed color population, yellow, orange and red morphs were equally attractive to hopliine beetles and did not differ significantly in terms of fruit set. Beetles were attracted to both red and yellow pan traps, but preferred the latter even at sites dominated by the red morph. We found no strong associations between morph color and abiotic factors, including soil chemistry. Plants in a common garden retained the capitulum color of the source population, even when grown from seed, suggesting that flower color variation is not a result of phenotypic plasticity. These results show that flower color in G. aurantiaca is geographically structured, but the ultimate evolutionary basis of this color variation remains elusive.

Differential expressions of anthocyanin synthesis genes underlie flower color divergence in a sympatric Rhododendron sanguineum complex

BACKGROUND

The Rhododendron sanguineum complex is endemic to alpine mountains of northwest Yunnan and southeast Tibet of China. Varieties in this complex exhibit distinct flower colors even at the bud stage. However, the underlying molecular regulations for the flower color variation have not been well characterized. Here, we investigated this via measuring flower reflectance profiles and comparative transcriptome analyses on three coexisting varieties of the R. sanguineum complex, with yellow flush pink, bright crimson, and deep blackish crimson flowers respectively. We compared the expression levels of differentially-expressed-genes (DEGs) of the anthocyanin / flavonoid biosynthesis pathway using RNA-seq and qRT-PCR data. We performed clustering analysis based on transcriptome-derived Single Nucleotide Polymorphisms (SNPs) data, and finally analyzed the promoter architecture of DEGs.

RESULTS

Reflectance spectra of the three color morphs varied distinctively in the range between 400 and 700 nm, with distinct differences in saturation, brightness, hue, and saturation/hue ratio, an indirect measurement of anthocyanin content. We identified 15,164 orthogroups that were shared among the three varieties. The SNP clustering analysis indicated that the varieties were not monophyletic. A total of 40 paralogous genes encoding 12 enzymes contributed to the flower color polymorphism. These anthocyanin biosynthesis-related genes were associated with synthesis, modification and transportation properties (RsCHS, RsCHI, RsF3H, RsF3'H, RsFLS, RsANS, RsAT, RsOMT, RsGST), as well as genes involved in catabolism and degradation (RsBGLU, RsPER, RsCAD). Variations in sequence and cis-acting elements of these genes might correlate with the anthocyanin accumulation, thus may contribute to the divergence of flower color in the R. sanguineum complex.

CONCLUSIONS

Our results suggested that the varieties are very closely related and flower color variations in the R. sanguineum complex correlate tightly with the differential expression levels of genes involved in the anabolic and catabolic synthesis network of anthocyanin. Our study provides a scenario involving intricate relationships between genetic mechanisms for floral coloration accompanied by gene flow among the varieties that may represent an early case of pollinator-mediated incipient sympatric speciation.