Postgenital Fusion Research Articles

Floral ontogeny reveals potential synapomorphies for Senegalia sect. Monacanthea p.p. (Leguminosae).

Senegalia was recently described as non-monophyletic; however, its sections exhibit robust monophyletic support, suggesting a potential reclassification into separate genera-Senegalia sect. Monocanthea p.p. is the largest section. It contains 164 species of pantropical distribution and includes all of the current 99 neotropical species of Senegalia; however, no morphological characteristics are available to differentiate this section. To characterize this section, we examined floral developmental traits in four species of Senegalia sect. Monocanthea p.p. These traits were previously considered as potentially distinguishing features within Acacia s.l. and include the onset patterns of the androecium, the timing of calyx union, the origin of the staminal disc, and the presence of stomata on the petals. Furthermore, we analyzed previously unexplored traits, such as corolla union types, inflorescence development, and micromorphological features related to the indumentum, as well as the presence and location of stomata. The characteristics proposed as potential synapomorphies of the group include the postgenital fusion of the corolla and the presence of a staminal disc formed at the base of the filaments. The other analyzed floral characteristics were not informative for the characterization of the group. Future studies of floral ontogeny will help to establish more precise patterns, mainly whether corolla union and staminal tube formation occur similarly in African and Asian sections of Senegalia.

Ledebouria socialis As a Key to Understanding the Evolution of Gynoecium in Asparagales.

For Ledebouria socialis, a superior ovary with interlocular septal nectaries that are confined to both ascidiate and plicate zones of the carpel is typical. It is impossible to describe the gynoecium zonation consistently, since the existing terminology does not allow us to display all its peculiarities. A part of the nectaries located in the gynophore and ascidiate zone is internalized from the very beginning of development and postgenital fusion is not required for their formation. For the formation of the distal part of the nectary confined to the plicate zone of the carpel, postgenital fusion is required to isolate nectar cavities from the center of the gynoecium. The nectary is internalized along the gynoecium periphery through the outgrowth of receptacle tissues. The structure of nectaries, as in Ledebouria, can be found in many Asparagales with a superior ovary.

Structure and Development of Flowers and Inflorescences in Burmannia (Burmanniaceae, Dioscoreales).

Species of the genus Burmannia possess distinctive and highly elaborated flowers with prominent floral tubes that often bear large longitudinal wings. Complicated floral structure of Burmannia hampers understanding its floral evolutionary morphology and biology of the genus. In addition, information on structural features believed to be taxonomically important is lacking for some species. Here we provide an investigation of flowers and inflorescences of Burmannia based on a comprehensive sampling that included eight species with various lifestyles (autotrophic, partially mycoheterotrophic and mycoheterotrophic). We describe the diversity of inflorescence architecture in the genus: a basic (most likely, ancestral) inflorescence type is a thyrsoid comprising two cincinni, which is transformed into a botryoid in some species via reduction of the lateral cymes to single flowers. Burmannia oblonga differs from all the other studied species in having an adaxial (vs. transversal) floral prophyll. For the first time, we describe in detail early floral development in Burmannia. We report presence of the inner tepal lobes in B. oblonga, a species with reportedly absent inner tepals; the growth of the inner tepal lobes is arrested after the middle stage of floral development of this species, and therefore they are undetectable in a mature flower. Floral vasculature in Burmannia varies to reflect the variation of the size of the inner tepal lobes; in B. oblonga with the most reduced inner tepals their vascular supply is completely lost. The gynoecium consists of synascidiate, symplicate, and asymplicate zones. The symplicate zone is secondarily trilocular (except for its distal portion in some of the species) without visible traces of postgenital fusion, which prevented earlier researchers to correctly identify the zones within a definitive ovary. The placentas occupy the entire symplicate zone and a short distal portion of the synascidiate zone. Finally, we revealed an unexpected diversity of stamen-style interactions in Burmannia. In all species studied, the stamens are tightly arranged around the common style to occlude the flower entrance. However, in some species the stamens are free from the common style, whereas in the others the stamen connectives are postgenitally fused with the common style, which results in formation of a gynostegium.

Gynoecium structure in Sapindales and a case study of Trichilia pallens (Meliaceae).

Sapindales is a monophyletic order within the malvid clade of rosids. It represents an interesting group to address questions on floral structure and evolution due to a wide variation in reproductive traits. This review covers a detailed overview of gynoecium features, as well as a new structural study based on Trichilia pallens (Meliaceae), to provide characters to support systematic relationships and to recognize patterns of variations in gynoecium features in Sapindales. Several unique and shared characteristics are identified. Anacrostylous and basistylous carpels may have evolved multiple times in Sapindales, while ventrally bulging carpels are found in pseudomonomerous Anacardiaceae. Different from previous studies, similar gynoecium features, including degree of syncarpy, ontogenetic patterns, and PTTT structure, favors a closer phylogenetic proximity between Rutaceae and Simaroubaceae, or Rutaceae and Meliaceae. An apomorphic tendency for the order is that the floral apex is integrated in the syncarpous or apocarpous gynoecium, but with different length and shape among families. Nitrariaceae shares similar stigmatic features and PTTT structure with many Sapindaceae. As the current position of both families in Sapindales is uncertain, floral features should be investigated more extensively in future studies. Two different types of gynophore were identified in the order: either derived from intercalary growth below the gynoecium as a floral internode, or by extension of the base of the ovary locules as part of the gynoecium. Sapindales share a combination of gynoecial characters but variation is mostly caused by different degrees of development of the synascidiate part relative to the symplicate part of carpels, or the latter part is absent. Postgenital fusion of the upper part of the styles leads to a common stigma, while stylar lobes may be separate. Due to a wide variation in these features, a new terminology regarding fusion is proposed to describe the gynoecium of the order.

Flower and Spikelet Construction in Rapateaceae (Poales).

The family Rapateaceae represents an early-divergent lineage of Poales with biotically pollinated showy flowers. We investigate developmental morphology and anatomy in all three subfamilies and five tribes of Rapateaceae to distinguish between contrasting hypotheses on spikelet morphology and to address questions on the presence of nectaries and gynoecium structure. We support an interpretation of the partial inflorescence (commonly termed spikelet), as a uniaxial system composed of a terminal flower and numerous empty phyllomes. A terminal flower in an inflorescence unit is an autapomorphic feature of Rapateaceae. The gynoecium consists of synascidiate, symplicate, and usually asymplicate zones, with gynoecium formation encompassing congenital and often also postgenital fusions between carpels. Species of Rapateaceae differ in the relative lengths of the gynoecial zones, the presence or absence of postgenital fusion between the carpels and placentation in the ascidiate or plicate carpel zones. In contrast with previous reports, septal nectaries are lacking in all species. The bird-pollinated tribe Schoenocephalieae is characterized by congenital syncarpy; it displays an unusual type of gynoecial (non-septal) nectary represented by a secretory epidermis at the gynoecium base.

Flower structure and development in Pennantiaceae: uncovering diversity of pseudomonomerous gynoecia in the basal grade of the order Apiales

Abstract Pseudomonomerous gynoecia with three (or four) carpels are unknown in the species-rich core group of Apiales, but this condition is shared by three species-poor families (Pennantiaceae, Torricelliaceae, Griseliniaceae) that form the basal grade of the order. Testing a hypothesis on the ancestral nature of carpel dimorphism in Apiales requires comparative data for all three lineages in this grade. We provide the first detailed description of flowers, including floral vasculature and gynoecium development, in a member of Pennantiaceae (Pennantia corymbosa). In contrast to many other Apiales, the inflorescence of Pennantia is paniculate and therefore has an unstable number of phyllomes in axes terminated by flowers. All phyllomes in the inflorescence are shifted onto lateral branches they subtend exhibiting recaulescence, a pattern that has not been reported elsewhere in Apiales. Plants are dioecious with functionally unisexual flowers. There are normally five stamens alternating with five petals. Anthers are present and produce pollen in stamens of male as well as female flowers, but ventral microsporangia are reduced in some anthers of female flowers. Anther morphology sometimes varies even among stamens of the same flower. Two types of synthecal anthers are recorded. Pollen dimorphism is confirmed: inaperturate pollen produced by stamens of female flowers supposedly acts as the only reward for pollinators in the absence of nectaries. The gynoecium of the female flower is syncarpous and pseudomonomerous: only one of three carpels is fertile. The gynoecium is initiated as three carpel primordia (future stigmas). One of them is smaller than the other two and occupies an alternistaminal (and antepetalous) position. The two large carpel primordia are located in the radii of stamens that are generally smaller (early in development) than the three other stamens. The carpel dimorphism is maintained at anthesis. The carpel with the smaller stigma is fertile, and those with larger stigmas are sterile. The carpels are congenitally united below the stigmas. The ovary is superior, unilocular (vs. inferior and plurilocular in Torricelliaceae and Griseliniaceae) and usually uniovulate with pendent ovule(s) inserted at the cross-zone level of the fertile carpel. As in most other Apiales, the short symplicate zone is sealed by postgenital fusion at anthesis and forms an internal compitum. The fertile carpel of the members of the basal grade of Apiales investigated so far is uniformly arranged in a petal radius. This is consistent with the idea that pseudomonomery is associated with stable patterns of flower groundplan in Apiales. Our data do not provide any clear structural or developmental evidence of independent origins of carpel dimorphism in Pennantiaceae, Torricelliaceae and Griseliniaceae.

Postgenital Fusion and Epidermal Cell Fate Control during Gynoecium Development

Postgenital Fusion and Epidermal Cell Fate Control during Gynoecium Development

Different ways to obtain similar results: the development of the corolla and epipetaly in Rubieae (Rubioideae, Rubiaceae)

Background and aims – Rubieae is a tribe in the subfamily Rubioideae characterised by herbaceous plants with verticillate leaves and flowers with a rudimentary or absent calyx and a short, cup-shaped corolla. This is in contrast to the flowers of most other Rubiaceae, in which the tubular corolla is longer than the corolla lobes. Also, the description by Payer, a French 19th century pioneer of floral ontogenetic research, of the floral development in Asperula, Galium, and Rubia deviates from recent insights about the development of tubular corollas, which are based on investigations of flowers of tropical Rubiaceae. Tubular corollas are currently considered as resulting from the development of underlying annular intercalary meristems, whereas Payer explained the tubular corollas in the three taxa by postgenital fusion. We therefore tested both hypotheses in six Rubieae genera, including the three taxa studied by Payer.Methods – Floral ontogeny of ten species in six Rubieae genera based on scanning electron (SEM) and light microscopy (LM). Conclusions – Our results suggest that, in all species studied, the mature phenotype of the corolla as well as the epipetaly of the stamens is caused by a combination of three developmental processes (the development of a stamen-corolla tube, the development of a corolla tube sensu stricto, and postgenital fusion), and the relative moment of activation of each of these processes during floral development (plastochron variation or heterochrony).

Arabidopsis ECERIFERUM3 (CER3) Functions to Maintain Hydration for Pollen–Stigma Recognition During Fertilization

Plant stigmas distinguish the pollen grains and allow compatible ones to fertilize female gametes. To analyze the underlying mechanism, conditional male-sterile mutations with impaired pollen coat and pollen–stigma recognition were isolated. The mutant pollen could germinate in vitro but not in vivo, suggesting that they are viable. The mutant stigma cells that contacted their own pollen-generated callose, a carbohydrate typically produced in response to foreign pollen. The defects of pollen hydration and fertilization in the mutants were rescued by high humidity, indicating that hydration is required for pollen–stigma interaction. Pollination with mixture of wild type and mutant pollens demonstrated that the pollen–stigma recognition of mutant pollen was disrupted. The mutant plants exhibited lack of stem waxes and postgenital fusion between aerial floral organs. In addition, the mutant pollen was deficient in very-long-chain lipids and had excess tryphine. Transmission electron microscopy analysis showed that mutant pollen had almost the same surface structure as the wild type at bicellular pollen stage. However, abnormal plastoglobuli were observed in the plastids of the mutant tapetum, which was an indicative of altered lipid accumulation. CER3 transcripts were found in anther tapetum and microspores at development stage 9. Our data reveal that CER3 is required for biosynthesis of tryphine lipids which function to maintain hydration for pollen–stigma recognition during fertilization.

Developmental sequence of the syncarpous gynoecium of Sarracenia purpurea (Sarraceniaceae) with flattened and broadened carpels and an umbrella-shaped style

The umbrella-shaped style of Sarracenia has a flattened and broadened distal half forming an umbrella canopy, and a slender cylindrical proximal half forming an umbrella stalk. The developmental sequence that gives rise to this unique structure has never been studied in detail. Data from light microscopy and scanning electron microscopy showed that the five carpels are initiated as discrete primordia, which then undergo congenital fusion and conduplicate folding and become a pentagonal syncarpous gynoecium. The distal region of the carpel then bends abaxially and undergoes significant expansion via a marginal meristem, forming the umbrella shape. Carpel closure is achieved via postgenital fusion at both transverse and longitudinal slits. Each of the five pollen tube transmitting tracts is enclosed by the adaxial surface of the carpel, and the inner epidermis of the umbrella canopy represents the expanded abaxial surface of the carpels, whereas the outer epidermis represents the expanded distal region of the fused carpellary margins. Epidermal trichomes develop first, then secretory glands and stomata appear later at the same stage on the umbrella canopy. This study provides insights into the evolution of the umbrella-shaped style utilizing both common and specialized carpel developmental programs with a novel spatial and temporal pattern.

Arabidopsis HSP70-16 is required for flower opening under normal or mild heat stress temperatures.

Sepals play important roles in protecting inner floral organs from various stresses and in guaranteeing timely flower opening. However, the exact role of sepals in coordinating interior and exterior signals remains elusive. In this study, we functionally characterized a heat shock protein gene, Arabidopsis HSP70-16, in flower opening and mild heat stress response, using combined genetics with anatomic, physiological, chemical, and molecular analyses. We showed that HSP70-16 is required for flower opening and mild heat response. Mutation of HSP70-16 led to a significant reduction in seed setting rate under 22°C, which was more severe at 27°C. Mutation of HSP70-16 also caused postgenital fusion at overlapping tips of two lateral sepals, leading to failed flower opening, abnormal floral organ formation, and impaired fertilization and seed setting. Chemical and anatomic analyses confirmed specific chemical and morphological changes of cuticle property in mutant lateral sepals, and qRT-PCR data indicated that expression levels of different sets of cuticle regulatory and biosynthetic genes were altered in mutants grown at both 22°C and 27°C temperatures. This study provides a link between thermal and developmental perception signals and expands the understanding of the roles of sepal in plant development and heat response.

The unusual gynoecium structure and extragynoecial pollen-tube pathway in Phytolacca (Phytolaccaceae)

The fusion of carpels into a unified compound gynoecium is considered a dominant feature of angiosperm evolution and it also occurs by postgenital fusion during the gynoecium development in some apocarpous species. However, we found the reverse process, the separation of carpels from combined carpel primordia, during the development of the gynoecium in Phytolacca. Semithin sectioning and scanning electron microscopy were utilised to observe the structure and development of the gynoecia in Phytolacca acinosa and Phytolacca americana, fluorescence microscopy was utilised to observe the pollen tube growth in the gynoecia of the two species, and the topology method was applied to analyze the relationship between the gynoecium structure and pollen tube pathway. Although the gynoecia of P. acinosa and P. americana are both syncarpous, the degree of carpel fusion in the mature gynoecia of the two syncarpous species is different as a result of variant developmental processes. However, change in the degree of carpel fusion during the development of gynoecia in Phytolacca does not affect pollen tube growth because of the existence of the extragynoecial pollen-tube pathway. Thus, the change in the degree of carpel fusion in Phytolacca is primarily the result of diversification of developmental processes related to selection pressure.

Exploring Cell Wall Composition and Modifications During the Development of the Gynoecium Medial Domain in Arabidopsis.

In Arabidopsis, the gynoecium, the inner whorl of the flower, is the female reproductive part. Many tissues important for fertilization such as the stigma, style, transmitting tract, placenta, ovules, and septum, comprising the medial domain, arise from the carpel margin meristem. During gynoecium development, septum fusion occurs and tissues form continuously to prepare for a successful pollination and fertilization. During gynoecium development, cell wall modifications take place and one of the most important is the formation of the transmitting tract, having a great impact on reproductive competence because it facilitates pollen tube growth and movement through the ovary. In this study, using a combination of classical staining methods, fluorescent dyes, and indirect immunolocalization, we analyzed cell wall composition and modifications accompanying medial domain formation during gynoecium development. We detected coordinated changes in polysaccharide distribution through time, cell wall modifications preceding the formation of the transmitting tract, mucosubstances increase during transmitting tract formation, and a decrease of mannan distribution. Furthermore, we also detected changes in lipid distribution during septum fusion. Proper cell wall composition and modifications are important for postgenital fusion of the carpel (septum fusion) and transmitting tract formation, because these tissues affect plant reproductive competence.

The histological study in sympetalous corolla development of pinwheel-type flowers of Saintpaulia

In this study, we revealed how the petals of Saintpaulia fuse into a corolla by using pinwheel phenotype cultivars. Striped patterns in petal, called pinwheel in Saintpaulia, are attractive phenotypes and thought to be the result of periclinal chimerism. For the selection of a genuine periclinal chimeric cultivar from three pinwheel cultivars, adventitious shoots were induced from leaf lamina. Shoot regeneration was observed from the epidermis in all cultivars by microscopic observation. All regenerated shoots from ‘Kaname’ flowered as monochromatic pink flowers, corresponding to an L1 phenotype of the cultivar. From the other two cultivars, many shoots flowered not only as an epidermal phenotype but also as a phenotype of the inner layer. In addition, shoot regeneration was induced from epidermis-peeled petioles from these three cultivars. All shoots from ‘Kaname’ flowered as monochromatic blue flowers, corresponding to an L2 phenotype. On the other hand, many shoots from ‘Kilauea’ flowered not only as monochromatic flowers, corresponding to an L2 phenotype, but also as bi-colored flowers. ‘Innocent Pink’ did not produce shoots from epidermal-peeled petioles. These results suggested that ‘Kaname’ is a genuine periclinal chimera, while the other two cultivars have other mechanisms for pinwheel expression. Genomic PCR using primers that amplifies almost the full length of flavonoid 3′,5′-hydroxylase (F3ʹ5ʹH) revealed the gene to be non-functional in pink flowers from L1 of ‘Kaname’. From monochromatic pink plants and pink portions of the corolla of ‘Kaname’, full-length F3ʹ5ʹH was not amplified. Similar results were obtained by quantitative PCR. Finally, we observed the fused portion of the petals and revealed that the petal fusion did not occur by postgenital fusion but by “connection”. The process, in Saintpaulia, comprises periclinal cell division in L1 during petal development, active cell division at the edge of the petal, adhesion to the next petals, and fusion. These steps create a striped flower color in Saintpaulia.

Ancestral traits and specializations in the flowers of the basal grade of living angiosperms

AbstractNew morphological and phylogenetic data prompt us to present an updated review of floral morphology and its evolution in the basal ANITA grade of living angiosperms, Chloranthaceae, and Ceratophyllum. Floral phyllotaxis is complex whorled in Nymphaeales and spiral in Amborella and Austrobaileyales. It is unresolved whether phyllotaxis was ancestrally whorled or spiral, but if it was whorled, the whorls were trimerous. The flowers are probably ancestrally bisexual because in most families with unisexual flowers these flowers exhibit rudiments of the opposite sex. Carpels are largely ascidiate and the closure line is short, either transverse or longitudinal. A style is usually absent or, if present, generally short and not plicate. Angiospermy (carpel sealing) is by secretion, rather than postgenital fusion, except in large‐flowered Nymphaeales and in Illicium, correlated with unusual fruits. Carpels with a single, median, pendent ovule are probably plesiomorphic. Chloranth‐ aceae and Ceratophyllaceae have an unsettled phylogenetic position, but in some phylogenetic analyses they form a clade, which may be sister to the remaining mesangiosperms (Magnoliidae, monocots, eudicots). This position is supported by their carpel characters, which are similar to those of the ANITA grade and different from those of most other mesangiosperms.

A developmental model for the corolla in Rubiaceae. Cryptic character states in corollas of the Spermacoceae alliance

Background and aims – In Rubiaceae, most flowers have a tubular corolla. Earlier studies showed that a tubular corolla may develop from an annular primordium or result from postgenital fusion of petals. Often stamen-corolla tubes are formed, concurring with epipetaly. Moreover, flowers with a fenestrated tubular corolla occur. The scattered distribution of species with corolla splits in Rubiaceae suggests a multiple origin. We intended to answer the following questions: (1) should the tubular corollas studied be assigned to a single or to several character states?; and (2) are the corolla splits studied homologous? We investigated the corolla development in five species of the Spermacoceae alliance with corolla splits in comparison with a Spermacoce species without. Methods – Floral developmental studies using scanning electron microscopy (SEM) and light microscopy (LM). Results – In Spermacoce, the tubular corolla with epipetalous stamens originates from an annular primordium. In Sacosperma and Pentas, the tubular corolla develops similarly with the stamens fixed basally. In Paederia and Pentodon, individual petal primordia originate on a ring wall. Next, stamen primordia appear adaxially on the ring wall. Then, the bases of the petals fuse partially, resulting in fenestrated tubular corollas. In Sacosperma and Pentas, corolla splits are actively formed in an initially closed tubular corolla. Conclusions – The tubular corollas of the species studied in Spermacoce, Sacosperma and Pentas are early sympetalous. Those in Paederia and Pentodon are late sympetalous. The tubular corolla results from a combination of three developmental processes: the formation of (1) a stamen-corolla tube, (2) a corolla tube sensu stricto, and (3) postgenital fusion of petals. The final form of the tubular corolla and the stamen insertion depend on the relative activity of these processes. Consequently, similar looking tubular corollas may constitute different character states. The corolla splits studied constitute two different cryptic character states in respectively Sacosperma / Pentas and Paederia/Pentodon .

The structure and development of incompletely closed carpels in an apocarpous species, Sagittaria trifolia (Alismataceae).

• Premise of the study: Carpel closure is commonly considered as a key innovation in angiosperms; however, some families continue to exhibit a variety of forms of incomplete carpel closure. The carpel of Sagittaria species contains an unusual structure. In this study, we confirm the closure type of the carpel of Sagittaria trifolia and discuss its development and evolution.• Methods: Scanning electron microscopy and light microscopy of semithin sections were used to observe the development and the mature structure of the carpel. Pollen tube growth in the carpel and seed germination in the achene was also studied.• Key results: During late carpel development, the middle parts of the carpel margins underwent postgenital fusion. However, at maturity the lowest and uppermost parts of the carpel margins remained open. The mature carpel was incompletely closed and contained a secretion-filled canal, which extended from the stigma to the opening at the carpel base. At that site, pollen tubes could either grow to the ovule or exit the carpel and grow to other carpels. The basal opening also served as an exit point for the seedling to emerge.• Conclusions: Incomplete carpel closure by S. trifolia differs from the closure types recorded in previous studies because two entrances link the ovary in the carpel to the outside environment. This type of carpel closure occurs as a result of the lack of fusion of the carpel margins at the base of the carpel and could improve the seed set and seedling germination of S. trifolia.

Floral structure and organogenesis of the wax palm Ceroxylon ceriferum (Arecaceae; Ceroxyloideae)

Most palm systematists were surprised when molecular evidence pointed to a sister group relationship between the tribe Ceroxyleae and the phytelephantoid palms. The latter comprises three genera of morphological aberrant palms that have previously been considered a subfamily of their own. Here we present the results of a detailed study of the floral structure and development of the wax palm, Ceroxylon ceriferum, which aims at revealing derived traits shared by the sister tribes Ceroxyleae and Phytelepheae. A series of floral stages were sampled from Ceroxylon ceriferum growing in the central coastal range of Venezuela. The samples were prepared for scanning electronic microscopy and serial anatomical sectioning. The development of male and female flowers of Ceroxylon ceriferum was similar. The receptacle elongated early in the ontogeny. The perianth was differentiated into distinct sepals and petals and was characterized by a lack of postgenital fusion. The stamens were incepted centripetally in 2(-3) whorls. The outer whorl of three stamens was antesepalous. The inner whorl consisted of six stamens arranged in three antepetalous pairs. The flowers of Ceroxylon ceriferum share a lack of postgenital fusion in the perianth with members of the tribe Phytelepheae. The elongation of the receptacle is reminiscent of the receptacle expansion in Phytelepheae. However, the multistaminate condition in C. ceriferum is less extreme than in the Phytelepheae, and the stamen initiation is centripetal as opposed to centrifugal in the latter.

CLV1 interacts with UFO in modulation of gynoecium development in Arabidopsis thaliana

The gynoecium is the female reproductive structure in flowering plants. It has been known that the CLAVATA1 (CLV1) gene regulates the floral meristem maintenance and floral organ number in Arabidopsis thaliana. However, whether CLV1 plays roles in gynoecium development remains uncharacterized. In this study, we showed that CLV1 genetically interacts with Unusual Floral Organs (UFO) to regulate the development of Arabidopsis gynoecium. Through forward genetic screen, we identified a clv1 allele, clv1-9, showing abnormal gynoecium development. Some epidermal cells on the growing inner surfaces of the clv1-9 gynoecium failed to fuse after contacting with each other, suggesting that CLV1 is essential for proper postgenital fusion. Furthermore, the ufo clv1-9 double mutant exhibited an expanded upper gynoecium, narrowed lower part of the ovary, altered vascular patterning and abaxial outward proliferation of the transmitting tract tissues. The transcription level of the ETT gene, which is required for gynoecium structure and pattern formation, was down-regulated in the ufo clv1-9 double mutant genoecia. Taken together, our results indicate that CLV1 functions together with UFO to regulate gynoecium development likely through modulating the expression of ETT.

Spurs in a Spur: Perianth Evolution in the Delphinieae (Ranunculaceae)

Delphinieae (Ranunculaceae) comprise ∼650 species of temperate herbs in Eurasia, North America, and Africa. Their zygomorphic flowers have been the object of numerous studies in morphology, ecology, and developmental genetics, and new phylogenetic insights make it timely to synthesize knowledge about their evolution. Key features of Delphinieae flowers are unusual nectaries consisting of paired organs of the inner perianth whorl that are completely enclosed by a single dorsal organ of the outer whorl. We investigated the floral development of five annual, unicarpellate species of Delphinium, focusing on perianth organization. The results show that the nectar-storing organ in these species results from the postgenital fusion of two primordia of the internal perianth whorl. Eleven floral traits traced on a phylogeny of Delphinieae reveal only two homoplasies in the perianth, namely, the nightcap shape of the dorsal organ of the external perianth whorl and the reduction of the internal perianth whorl to two ...