Perianth Development Research Articles

APETALA2-like Floral Homeotic Protein Up-Regulating FaesAP1_2 Gene Involved in Floral Development in Long-Homostyle Common Buckwheat.

In the rosid species Arabidopsis thaliana, the AP2-type AP2 transcription factor (TF) is required for specifying the sepals and petals identities and confers a major A-function to antagonize the C-function in the outer floral whorls. In the asterid species Petunia, the AP2-type ROB TFs are required for perianth and pistil development, as well as repressing the B-function together with TOE-type TF BEN. In Long-homostyle (LH) Fagopyrum esculentum, VIGS-silencing showed that FaesAP2 is mainly involved in controlling filament and style length, but FaesTOE is mainly involved in regulating filament length and pollen grain development. Both FaesAP2 (AP2-type) and FaesTOE (TOE-type) are redundantly involved in style and/or filament length determination instead of perianth development. However, neither FaesAP2 nor FaesTOE could directly repress the B and/or C class genes in common buckwheat. Moreover, the FaesAP1_2 silenced flower showed tepal numbers, and filament length decreased obviously. Interestingly, yeast one-hybrid (Y1H) and dual-luciferase reporter (DR) further suggested that FaesTOE directly up-regulates FaesAP1_2 to be involved in filament length determination in LH common buckwheat. Moreover, the knockdown of FaesTOE expression could result in expression down-regulation of the directly target FaesAP1_2 in the FaesTOE-silenced LH plants. Our findings uncover a stamen development pathway in common buckwheat and offer deeper insight into the functional evolution of AP2 orthologs in the early-diverging core eudicots.

Genome-wide identification and characterization of TCP gene family in Dendrobium nobile and their role in perianth development.

TCP is a widely distributed, essential plant transcription factor that regulates plant growth and development. An in-depth study of TCP genes in Dendrobium nobile, a crucial parent in genetic breeding and an excellent model material to explore perianth development in Dendrobium, has not been conducted. We identified 23 DnTCP genes unevenly distributed across 19 chromosomes and classified them as Class I PCF (12 members), Class II: CIN (10 members), and CYC/TB1 (1 member) based on the conserved domain and phylogenetic analysis. Most DnTCPs in the same subclade had similar gene and motif structures. Segmental duplication was the predominant duplication event for TCP genes, and no tandem duplication was observed. Seven genes in the CIN subclade had potential miR319 and -159 target sites. Cis-acting element analysis showed that most DnTCP genes contained many developmental stress-, light-, and phytohormone-responsive elements in their promoter regions. Distinct expression patterns were observed among the 23 DnTCP genes, suggesting that these genes have diverse regulatory roles at different stages of perianth development or in different organs. For instance, DnTCP4 and DnTCP18 play a role in early perianth development, and DnTCP5 and DnTCP10 are significantly expressed during late perianth development. DnTCP17, 20, 21, and 22 are the most likely to be involved in perianth and leaf development. DnTCP11 was significantly expressed in the gynandrium. Specially, MADS-specific binding sites were present in most DnTCP genes putative promoters, and two Class I DnTCPs were in the nucleus and interacted with each other or with the MADS-box. The interactions between TCP and the MADS-box have been described for the first time in orchids, which broadens our understanding of the regulatory network of TCP involved in perianth development in orchids.

Floral structure and development in Nandina domestica and implications for systematic affinities in Berberidaceae and perianth evolution in Ranunculales

Abstract In Berberidaceae, the phylogenetic position and systematic affinities of the monotypic genus Nandina have long been debated and remain unclear. In addition, previous comparative studies have provided conflicting reports on the origin and development of its petals. Using scanning electron microscopy and microtome sections, we studied the structure and development of the flower and perianth in Nandina domestica to re-evaluate its affinities and homology of its petals. Our results confirm that N. domestica essentially shares the same Bauplan (organization) with other Berberidaceae and its petals are neither delayed in development nor much differentiated from sepals. However, we sometimes also observed the initiation of additional primordia that become confluent with the base of stamens of the outer whorl, but do not develop further and are no longer visible in later stages of development. Our study thus not only reconciles previous conflicting interpretations on the origin and development of petals in Nandina, but also confirms that it has a unique suite of vegetative and reproductive features supporting its position as a distinct member of the family. In addition, it suggests that the most recent common ancestors of both Berberidaceae and Ranunculales probably had two types of petaloid organs with distinct origin and development but still sharing a deep common genetic identity.

An unusual plane tree from the Early Cretaceous of Kansas, USA

We present a new genus and species of platanaceous inflorescences from the Hoisington III locality of Barton County, Kansas, USA. This locality lies within the Albian Dakota Formation, which was formed from deposits along the eastern margin of the mid-Cretaceous North American Western Interior Seaway. The elongate inflorescences documented here are unusual for Platanaceae, which is known for its globose, unisexual inflorescences. Distefananthus hoisingtonensis Huegele and Wang gen. et sp. nov. has elongate, cylindrical, ellipsoid, pedunculate inflorescences bearing apocarpous achenes with long styles, borne in florets of 3-4, with over 100 fruits per inflorescence, and stamens with short filaments and hairy apical connectives. The small and relatively fixed number of parts per floret ((3-)4 fruits and c. 3-4 stamens) is seen in other Cretaceous Platanaceae inflorescences and may have facilitated insect pollination. The state of perianth development is unclear, and the fruits lack basal dispersal hairs. The Hoisington material encompasses a developmental sequence; younger inflorescences bear a mix of stamens and immature carpels (thin with long styles) while mature inflorescences bear developed fruits (thicker and often with broken styles) and have lost all stamens. Like the typical globose capitula, the elongate inflorescences probably originated from the reduction of a compound inflorescence. The elongate inflorescences may represent a less compressed, ancestral or pleisiomorphic condition for Platanaceae. The only other species from this family known for elongate inflorescences is from the Paleocene and Eocene of western North America. The inflorescences from Hoisington co-occur with Sapindopsis leaves. At this locality, Sapindopsis powelliana occurs at a similar frequency to the elongate inflorescences and is a possible candidate for the leaves associated with them. The Hoisington material marks the earliest known occurrence of bisexual inflorescences in Platanaceae. The discovery of Distefananthus hoisingtonensis offers new insight into the diversity of platanaceous inflorescences in the mid-Cretaceous, a critical early period in the history of Platanaceae.

Floral ontogeny ofDelphinium anthriscifolium(Ranunculaceae) and development of intrafloral and symmetrical resupinated organs

AbstractDelphinieae (Ranunculaceae) are characterized by zygomorphic spiral flowers and show a remarkable diversity of perianth organization. Floral structure and development have been investigated in most lineages of the tribe, mainly focusing on the establishment of symmetry and on perianth development. In this study, floral organogenesis and morphogenesis in Delphinium anthriscifolium, a member of the recently erected Delphinium subgenus Anthriscifolium, were investigated and compared with those of other species of Delphinieae in a phylogenetic context. In D. anthriscifolium, zygomorphy of the spiral flower is established soon after the initiation of sepal primordia. Among the four fully developed petals of the dorsoventralized corolla, the two dorsalmost ones become spurred, and the lateral petals resupinate before anthesis and are mirror images of each other. Resupination of petals, long overlooked in morphological studies of Delphinieae, is here reported in Ranunculaceae for the first time. The role of resupinated petals, possibly acting as a landing platform for nectar foragers, may be of high adaptive significance. Based on our new findings regarding floral ontogeny and morphology in D. anthriscifolium, we provide an updated picture of floral evolution in Delphinieae.

Extending the Toolkit for Beauty: Differential Co-Expression of DROOPING LEAF-Like and Class B MADS-Box Genes during Phalaenopsis Flower Development.

The molecular basis of orchid flower development is accomplished through a specific regulatory program in which the class B MADS-box AP3/DEF genes play a central role. In particular, the differential expression of four class B AP3/DEF genes is responsible for specification of organ identities in the orchid perianth. Other MADS-box genes (AGL6 and SEP-like) enrich the molecular program underpinning the orchid perianth development, resulting in the expansion of the original “orchid code” in an even more complex gene regulatory network. To identify candidates that could interact with the AP3/DEF genes in orchids, we conducted an in silico differential expression analysis in wild-type and peloric Phalaenopsis. The results suggest that a YABBY DL-like gene could be involved in the molecular program leading to the development of the orchid perianth, particularly the labellum. Two YABBY DL/CRC homologs are present in the genome of Phalaenopsis equestris, PeDL1 and PeDL2, and both express two alternative isoforms. Quantitative real-time PCR analyses revealed that both genes are expressed in column and ovary. In addition, PeDL2 is more strongly expressed the labellum than in the other tepals of wild-type flowers. This pattern is similar to that of the AP3/DEF genes PeMADS3/4 and opposite to that of PeMADS2/5. In peloric mutant Phalaenopsis, where labellum-like structures substitute the lateral inner tepals, PeDL2 is expressed at similar levels of the PeMADS2-5 genes, suggesting the involvement of PeDL2 in the development of the labellum, together with the PeMADS2-PeMADS5 genes. Although the yeast two-hybrid analysis did not reveal the ability of PeDL2 to bind the PeMADS2-PeMADS5 proteins directly, the existence of regulatory interactions is suggested by the presence of CArG-boxes and other MADS-box transcription factor binding sites within the putative promoter of the orchid DL2 gene.

Evolution of the Subgroup 6 R2R3-MYB Genes and Their Contribution to Floral Color in the Perianth-Bearing Piperales.

Flavonoids, carotenoids, betalains, and chlorophylls are the plant pigments responsible for floral color. Anthocyanins, a class of flavonoids, are largely responsible for the red, purple, pink, and blue colors. R2R3-MYB genes belonging to subgroup 6 (SG6) are the upstream regulatory factors of the anthocyanin biosynthetic pathway. The canonical members of these genes in Arabidopsis include AtMYB75, AtMYB90, AtMYB113, and AtMYB114. The Aristolochiaceae is an angiosperm lineage with diverse floral groundplans and perianth colors. Saruma henryi exhibits a biseriate perianth with green sepals and yellow petals. All other genera have sepals only, with colors ranging from green (in Lactoris) to a plethora of yellow to red and purple mixtures. Here, we isolated and reconstructed the SG6 R2R3-MYB gene lineage evolution in angiosperms with sampling emphasis in Aristolochiaceae. We found numerous species-specific duplications of this gene lineage in core eudicots and local duplications in Aristolochiaceae for Saruma and Asarum. Expression of SG6 R2R3-MYB genes examined in different developmental stages and plant organs of four Aristolochiaceae species, largely overlaps with red and purple pigments, suggesting a role in anthocyanin and flavonoid synthesis and accumulation. A directed RNA-seq analysis corroborated our RT-PCR analyses, by showing that these structural enzymes activate during perianth development in Aristolochia fimbriata and that the regulatory genes are expressed in correlation with color phenotype. Finally, the reconstruction of the flavonoid and anthocyanin metabolic pathways using predicted peptides from transcriptomic data show that all pivotal enzymes are present in the analyzed species. We conclude that the regulatory genes as well as the biosynthetic pathway are largely conserved across angiosperms. In addition, the Aristolochiaceae emerges as a remarkable group to study the genetic regulatory network for floral color, as their members exhibit an outstanding floral diversity with elaborate color patterns and the genetic complement for SG6 R2R3-MYB genes is simpler than in core eudicot model species.

Insights into the ancestral flowers of Ranunculales

AbstractThe question of the origin of petals has long been debated in the botanical literature. Ranunculales are characterized by a spectacular floral diversity, particularly at the perianth level. Recent progress in understanding the genetic bases of floral organ identity suggests a single origin for petals in Ranunculaceae, contrasting with the traditional morphological hypothesis of repeated evolution. However, perianth evolution at the ordinal level remains incompletely understood. Recent advances in the elucidation of phylogenetic relationships in the order now provide a new opportunity to study character evolution with model-based methods. We used ancestral state reconstruction methods that take into account various sources of uncertainty to reconstruct the evolution of floral traits at the scale of Ranunculales using a consensus phylogenetic framework of 144 terminal species representing all families in the order. Ancestrally, Ranunculales probably had three trimerous whorls of perianth organs differentiated into two categories of petaloid organs differing in their shape. Each whorl was further lost or duplicated. Moreover, our results support the hypothesis of a single origin of highly specialized (elaborate) nectariferous petals in Ranunculaceae.

Characterization of Two AGL6–Like Genes from a Chinese Endemic Woody Tree, Manglietia patungensis (Magnoliaceae) Provides Insight into Perianth Development and Evolution in Basal Angiosperms

Manglietia patungensis (Magnoliaceae) exhibits radially symmetric flowers with perianth consisting of three separate sepaloid tepals in whorl 1 and six petaloid tepals in the inner two whorls, which shows an obvious difference from flowers of most Magnoliaceae species that contain three uniform petaloid tepals whorls, and make it an excellent model for understanding perianth morphology differentiation during early flower evolution. Here, two AGL6 orthologs, MapaAGL6-1 and MapaAGL6-2, were isolated from M. patungensis. Sequence alignment and phylogenetic analyses grouped both genes into the AGL6 lineage. MapaAGL6-1 is expressed only in the perianth whorls, while MapaAGL6-2 is strongly expressed in the perianth whorls but is lowly expressed in gynoecium. Furthermore, ectopic expression of MapaAGL6-1 results in strong complementation phenotypes in the Arabidopsis ap1-10 flower and production of normal floral organs in four floral whorls only with the petal number reduced in whorl 2, while ectopic expression of MapaAGL6-2 only results in petals partly rescued but failing to terminate carpelloid development in Arabidopsis ap1-10 mutant. In addition, the daughter lines generated from a cross between 35S::MapaAGL6-1 transgenic plants showing strong phenotypes and 35S::MapaAGL6-2 transgenic plants showing phenotypic changes produce normal flowers. Our results suggest that MapaAGL6-1 is a reasonable A-function gene controlling perianth identity in Magnoliaceae, which infers from its expression region and complementation phenotypes in Arabidopsis ap1 mutant, while MapaAGL6-2 is mainly involved in petaloid tepal development. Our data also provide a new clue to uncover the perianth development and early evolution in basal angiosperms.

Isolation and Characterization of the PISTILLATA Ortholog Gene from Cymbidium faberi Rolfe

Cymbidium faberi Rolfe is a very popular potted plant in China, Japan and Korea where it has been cultivated for centuries. The economic value of this popular native Asian orchid could be enhanced by changes in its floral traits. In Arabidopsis, PISTILLATA (PI) is involved in regulating petal and stamen development. In order to investigate the possible role of the PI ortholog involved in floral development, we isolated CyfaPI from C. faberi. Protein alignment and a phylogenetic tree grouped CyfaPI in the PI lineage. CyfaPI transcripts were detected in all floral organs, but were absent in leaves. Moreover, in flowers, the highest expression level of CyfaPI was present in the gynostemium and the lowest level was found in anther caps. In addition, ectopic expression of CyfaPI in Arabidopsis pi-1 mutant rescued petal development, and complement the development of filament-like structure (part of stamen), but failed to complement anther development in the stamen whorl. All these finding suggest that CyfaPI is mainly responsible for perianth and gynostemium development in C. faberi. Our data may help to trace the development of the gynostemium program and evolution in orchids.

How to Evolve a Perianth: A Review of Cadastral Mechanisms for Perianth Identity.

The flower of angiosperms is considered to be a major evolutionary innovation that impacted the whole biome. In particular, two properties of the flower are classically linked to its ecological success: bisexuality and a differentiated perianth with sepals and petals. Although the molecular basis for floral organ identity is well understood in extant species and summarized in the famous ABC model, how perianth identity appeared during evolution is still unknown. Here we propose that cadastral mechanisms that maintain reproductive organ identities to the center of the flower could have supported perianth evolution. In particular, repressing B- and C-class genes expression toward the inner whorls of the flower, is a key process to isolate domains with sepal and petal identity in the outer whorls. We review from the literature in model species the diverse regulators that repress B- and C-class genes expression to the center of the flower. This review highlights the existence of both unique and conserved repressors between species, and possible candidates to investigate further in order to shed light on perianth evolution.

Evolutionary diversification of CYC/TB1-like TCP homologs andtheir recruitment for the control of branching and floral morphology in Papaveraceae (basal eudicots).

Angiosperms possess enormous morphological variation in plant architectures and floral forms. Previous studies in Pentapetalae and monocots have demonstrated the involvement of TCP domain CYCLOIDEA/TEOSINTE BRANCHED1-like (CYC/TB1) genes in the control of floral symmetry and shoot branching. However, how TCP/CYC-like (CYL) genes originated, evolved and functionally diversified remain unclear. We conducted a comparative functional study in Ranunculales, the sister lineage to all other eudicots, between Eschscholzia californica and Cysticapnos vesicaria, two species of Papaveraceae with actinomorphic and zygomorphic flowers, respectively. Phylogenetic analysis indicates that CYL genes in Papaveraceae form two paralogous lineages, PapaCYL1 and PapaCYL2. Papaveraceae CYL genes show highly diversified expression patterns as well as functions. Enhanced branching by silencing of EscaCYL1 suggests that the role of CYC/TB1-like genes in branching control is conserved in Papaveraceae. In contrast to the arrest of stamen development in Pentapetalae, PapaCYL genes promote stamen initiation and growth. In addition, we demonstrate that CyveCYLs are involved in perianth development, specifying sepal and petal identity in Cysticapnos by regulating the B-class floral organ identity genes. Our data also suggest the involvement of CyveCYL genes in the regulation of flower symmetry in Cysticapnos. Our work provides evidence of the importance of TCP/CYC-like genes in the promotion of morphological diversity across angiosperms.

Organ Homologies and Perianth Evolution in the Dasymaschalon Alliance (Annonaceae): Inner Petal Loss and Its Functional Consequences.

The Dasymaschalon alliance within the early divergent angiosperm family Annonaceae comprises c. 180 species in four genera (Dasymaschalon, Desmos, Friesodielsia, and Monanthotaxis). The alliance offers an excellent opportunity for investigating perianth evolution and functional adaptations because of the presence of different numbers of petal whorls and contrasting floral chamber morphologies. The absence of the inner petal whorl in Dasymaschalon renders it distinctive in the family: previous studies have suggested that its three outermost stamens might be homologous with the inner petals of the sister genus, Friesodielsia, reflecting a homeotic shift of floral organ identify from inner petals to stamens. To investigate this hypothesis and general perianth evolution in the alliance, we (i) compared the floral vascularization of selected Dasymaschalon and Friesodielsia species using paraffin serial sectioning, and (ii) mapped selected perianth characters of inferred functional significance onto a molecular phylogenetic framework of the Dasymaschalon alliance (46 accessions; five cpDNA, and two nrDNA markers). The results indicate that the vasculature of the outermost stamen whorl of Dasymaschalon does not fuse with the perianth cortical vascular system, but instead splits from the basal traces of the free stamen bundles, contradicting previous inferences of homology with the inner corolla whorl of other Annonaceae. The loss of the inner petal whorl in Dasymaschalon is less likely to be due to a homeotic mutation, and instead possibly involved either the loss of genes that are responsible for determining inner petals or else the expression failure of these genes. Optimizations of perianth characters indicate that the absence of the inner petal whorl and the connivence of outer petals during anthesis are synapomorphic for Dasymaschalon. Circadian trapping of pollinators is inferred either to be derived in the stem lineage of the Dasymaschalon–Friesodielsia clade, or else to have evolved in parallel in the Dasymaschalon and Friesodielsia lineages. Subsequent changes in the remaining petals of Dasymaschalon flowers (which do not fully separate during anthesis) are likely to have enabled perpetuation of the circadian trapping mechanism, lessening the adverse impacts of inner petal loss.

B and E MADS-box genes determine the perianth formation in Cymbidium goeringii Rchb.f.

Cymbidium goeringii Rchb.f. is an important ornamental plant with a striking well-differentiated lip. Its complex floral architecture presents an exciting opportunity to examine perianth development. In flowering plants, class A, B and E floral homeotic genes play key roles in the specification of perianth identity. In this study, we used a cDNA library of wild-type C. goeringii flower buds for transcriptome sequencing. Eighteen candidate class A, B and E genes (including AP1/FUL-, AP2-, DEF-, GLO-, SEP- and AGL6-like genes) were identified. Quantitative real time polymerase chain reaction (qRT-PCR) results showed that CgDEF1, CgSEP2 and CgAGL6-1 were strongly detected only in the sepals and petals and were significantly downregulated in the lips. CgDEF3, CgDEF4 and CgAGL6-3 were highly expressed in the lips and lip-like petals but were only minimally detected in the sepals. Yeast two-hybrid analysis indicated that CgDEF1 and CgGLO formed a heterodimer. CgAGL6-1/CgSEP2 and CgDEF1 formed higher-order protein complexes with the assistance of the CgGLO protein, and both CgAGL6-1 and CgSEP2 formed a heterodimer. CgDEF3/CgDEF4 could interact independently with CgGLO and CgAGL6-3, respectively, while CgDEF3 and CgDEF4 also formed heterodimers with the assistance of the CgGLO. Based on a comprehensive analysis relating these gene expression patterns to protein interaction profiles, the mechanism of sepal/petal/lip determination was studied in C. goeringii. Furthermore, a hypothesis explaining the sepal/petal/lip determination of C. goeringii is proposed. The lip-quartet (CgDEF3/CgDEF4/CgAGL6-3/CgGLO) promoted lip formation, whereas the sepal/petal-quartet (CgDEF1/CgAGL6-1/CgSEP2/CgGLO) promoted sepal/petal formation. These results enrich the current knowledge regarding the mechanism and pathways of perianth formation in orchids.

Comparative Transcriptome Analysis between Gynoecious and Monoecious Plants Identifies Regulatory Networks Controlling Sex Determination in Jatropha curcas.

Most germplasms of the biofuel plant Jatropha curcas are monoecious. A gynoecious genotype of J. curcas was found, whose male flowers are aborted at early stage of inflorescence development. To investigate the regulatory mechanism of transition from monoecious to gynoecious plants, a comparative transcriptome analysis between gynoecious and monoecious inflorescences were performed. A total of 3,749 genes differentially expressed in two developmental stages of inflorescences were identified. Among them, 32 genes were involved in floral development, and 70 in phytohormone biosynthesis and signaling pathways. Six genes homologous to KNOTTED1-LIKE HOMEOBOX GENE 6 (KNAT6), MYC2, SHI-RELATED SEQUENCE 5 (SRS5), SHORT VEGETATIVE PHASE (SVP), TERMINAL FLOWER 1 (TFL1), and TASSELSEED2 (TS2), which control floral development, were considered as candidate regulators that may be involved in sex differentiation in J. curcas. Abscisic acid, auxin, gibberellin, and jasmonate biosynthesis were lower, whereas cytokinin biosynthesis was higher in gynoecious than that in monoecious inflorescences. Moreover, the exogenous application of gibberellic acid (GA3) promoted perianth development in male flowers and partly prevented pistil development in female flowers to generate neutral flowers in gynoecious inflorescences. The arrest of stamen primordium at early development stage probably causes the abortion of male flowers to generate gynoecious individuals. These results suggest that some floral development genes and phytohormone signaling pathways orchestrate the process of sex determination in J. curcas. Our study provides a basic framework for the regulation networks of sex determination in J. curcas and will be helpful for elucidating the evolution of the plant reproductive system.

High developmental lability in the perianth ofInga(Fabales, Fabaceae): a Neotropical woody rosid with gamopetalous corolla

Inga is a highly diverse Neotropical genus of Fabaceae with a rapid and recent diversification. Its flowers are actinomorphic with a wide variation in merism and size and length of perianth. Notwithstanding its species richness and economic importance, few floral ontogenetic studies have been carried out in this genus. Thus, we investigated perianth development and morphology of five Inga spp. using scanning electron and light microscopy. Perianth ontogeny is highly labile. Sepal and petal primordium number ranges from four to seven. The sequence of sepal initiation is generally reversed unidirectionally (from adaxial to abaxial side); petals are initiated simultaneously. The position of sepals and petals is variable among and within species. The sepal may be positioned adaxially, abaxially or slightly displaced in relation to the median sagittal plane. The median petal is positioned in the adaxial (I. congesta, I. grandis) or abaxial region (I. bella, I. hispida). Elongated petals touch each other apically through conspicuous papillae. Perianth development in Inga differs from that of other mimosoids. The early developmental stages show a wide variation. However, subsequent ontogenetic processes, known as equalization during intermediate stages, establish uniformity in the floral architecture, thus preventing possible functional disparities that could influence reproductive success.

Transcriptome and selected metabolite analyses reveal points of sugar metabolism in jackfruit (Artocarpus heterophyllus Lam.)

Artocarpus heterophyllus Lam., commonly known as jackfruit, produces the largest tree-borne fruit known thus far. The edible part of the fruit develops from the perianths, and contains many sugar-derived compounds. However, its sugar metabolism is poorly understood. A fruit perianth transcriptome was sequenced on an Illumina HiSeq 2500 platform, producing 32,459 unigenes with an average length of 1345nt. Sugar metabolism was characterized by comparing expression patterns of genes related to sugar metabolism and evaluating correlations with enzyme activity and sugar accumulation during fruit perianth development. During early development, high expression levels of acid invertases and corresponding enzyme activities were responsible for the rapid utilization of imported sucrose for fruit growth. The differential expression of starch metabolism-related genes and corresponding enzyme activities were responsible for starch accumulated before fruit ripening but decreased during ripening. Sucrose accumulated during ripening, when the expression levels of genes for sucrose synthesis were elevated and high enzyme activity was observed. The comprehensive transcriptome analysis presents fundamental information on sugar metabolism and will be a useful reference for further research on fruit perianth development in jackfruit.

Perianth evolution in Ranunculaceae: are petals ancestral in the family?

Progress has been made recently towards the elucidation of phylogenetic relationships among subfamilies and tribes of the Ranunculaceae – the most recent hypothesis was published in 2016 by our team. Although relationships among the 10 tribes of the subfamily Ranunculoideae remain incompletely supported, this hypothesis provides an interesting framework to address the key issue of the ancestral vs. derived nature of a differentiated perianth within the family, and at the level of Ranunculales as a whole. Here, we present ancestral state reconstructions for several perianth characters, such as differentiation into sepals and petals, shape of petals, presence/absence of nectaries, and petaloid or sepaloid aspect of sepals. Characters were scored using the PROTEUS database and optimized on the most recent phylogeny of Ranunculaceae using parsimony and maximum likelihood methods. The results are discussed with regard to recent evo-devo studies focused on identifying genes involved in floral organs identity (the so-called ABC model) in Ranunculales.

CsPI from the perianthless early-diverging Chloranthus spicatus show function on petal development in Arabidopsis thaliana.

BackgroundIn the floral ABC model, B-class genes comprised of DEFICIENS (DEF)/APETALA3 (AP3) and GLOBOSA (GLO)/PISTILLATA (PI) had been proposed to involve in second and third whorl floral organ development. However, less is known about the function of B-class genes from early-diverging angiosperms. Chloranthaceae is one of the early-diverging angiosperm families. In this study, we characterized the role of the PI-like gene CsPI cloned from Chloranthus spicatus which have the simplest perianthless bisexual flowers.ResultsThe expression profile analysis reveals high levels of CsPI mRNA in stamens in Chloranthus spicatus, with weak distribution in leaves and other floral organs. Nevertheless, CsPI rescued both stamen and petal development in Arabidopsis thaliana pi-1 mutants and caused partially conversion of sepals into petaloid organs in wild-type Arabidopsis thaliana plants. Yeast two-hybrid analysis showed that CsPI can form not only homodimers but also heterodimers with proteins encoded by Arabidopsis thaliana and Chloranthus spicatus AP3-like genes.ConclusionsThese results suggested that CsPI has an ancestral function on stamen development and that CsPI has capability to specify petal development in Arabidopsis thaliana. The finding indicates that the activity of the encoded PI-like proteins is highly conserved between the early-diverging Chloranthus and Arabidopsis. Moreover, our results appear to suggest that B-function genes may not play a role in perianth development in Chloranthus spicatus.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-55-21) contains supplementary material, which is available to authorized users.

Reevaluation of the perianth and androecium in Caryophyllales: implications for flower evolution

The Caryophyllales have the highest diversity in androecial patterns among flowering plants with stamen numbers ranging from 1 up to 4,000. Thanks to the recent progress in reconstructing the phylogeny of core Caryophyllales, questions of floral evolution, such as the origin and diversification of the androecium, can be readdressed. Caryophyllales are unique among core eudicots in sharing an androecial ring meristem or platform with centrifugal development of stamens and petals. Stamens are basically arranged in two whorls and evolution within the clade depends on the shift of either the antesepalous or the alternisepalous whorls to an upper position on the ring meristem and the reduction of the other. Four main developmental phenomena are responsible for the high diversity in androecial patterns: (1) the sterilisation of the outermost stamens through a division of common primordia; (2) the secondary addition of stamens by a centrifugal initiation of supernumerary stamens superimposed on a lower stamen number; (3) the pairwise displacement of alternisepalous stamens to the middle of the outer sepals and their potential fusion, or as part of a pluristaminate androecium; (4) the inversed sequence, reduction and loss of antesepalous stamens. Shifts in stamen numbers depend on pressures of the calyx and carpels and changes in the number of the latter. These patterns are expressed differently in the three main evolutionary lines of core Caryophyllales and are systematically relevant: (1) A basal grade of Caryophyllales, culminating with Caryophyllaceae, Amaranthaceae, Stegnosperma and Limeum, has the antesepalous stamens initiated in upper position on the ring meristem, and alternisepalous stamens are preferentially reduced. Among the antesepalous whorl there is a progressive loss of stamens following a sequence inversed to sepal initiation. Petaloid staminodes are formed by the radial division of outer stamens. (2) The raphide-clade and Molluginaceae are characterized by alternisepalous stamens in upper position on the ring meristem, with a trend to secondary stamen multiplication, and loss of antesepalous stamens. (3) The Portulacineae share the pattern of the raphide clade, but some taxa show shifts to an upper position on the ring meristem of either antesepalous or alternisepalous stamens, linked with secondary multiplications and reduction of either whorl. Different floral characters are plotted on a recent cladogram of Caryophyllales. The data show a consistent correlation between shifting carpel and stamen numbers independent of perianth evolution. Comparative data suggest that the basic androecium of Caryophyllales consists of two whorls of five stamens, linked with an absence of petals, and the evolution of the androecium is a combination of reductions and secondary multiplications of stamens with a highly predictive systematic value.