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Trichomes are specialized epidermal cells in aerial plant parts. Trichome development proceeds in three stages, determination of cell fate, specification, and morphogenesis. Most genes responsible for these processes have been identified in the unicellular branched leaf trichomes from the model Arabidopsis thaliana. Less is known about the molecular basis of multicellular trichome formation across flowering plants, especially those formed in floral organs of early diverging angiosperms. Here, we aim to identify the genetic regulatory network (GRN) underlying multicellular trichome development in the kettle-shaped trap flowers of Aristolochia (Aristolochiaceae). We selected two taxa for comparison, A. fimbriata, with trichomes inside the perianth, which play critical roles in pollination, and A. macrophylla, lacking specialized trichomes in the perianth. A detailed morphoanatomical characterization of floral epidermis is presented for the two species. We compared transcriptomic profiling at two different developmental stages in the different perianth portions (limb, tube, and utricle) of the two species. Moreover, we present a comprehensive expression map for positive regulators and repressors of trichome development, as well as cell cycle regulators. Our data point to extensive modifications in gene composition, expression, and putative roles in all functional categories when compared with model species. We also record novel differentially expressed genes (DEGs) linked to epidermis patterning and trichome development. We thus propose the first hypothetical genetic regulatory network (GRN) underlying floral multicellular trichome development in Aristolochia, and pinpoint key factors responsible for the presence and specialization of floral trichomes in phylogenetically distant species of the genus.

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

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BACKGROUND AND AIMS: The epidermis constitutes the outermost tissue of the plant body. Although it plays major structural, physiological and ecological roles in embryophytes, the molecular mechanisms controlling epidermal cell fate, differentiation and trichome development have been scarcely studied across angiosperms, and remain almost unexplored in floral organs. METHODS: In this study, we assess the spatio-temporal expression patterns of GL2, GL3, TTG1, TRY, MYB5, MYB6, HDG2, MYB106-like, WIN1 and RAV1-like homologues in the magnoliid Aristolochia fimbriata (Aristolochiaceae) by using comparative RNA-sequencing and in situ hybridization assays. KEY RESULTS: Genes involved in Aristolochia fimbriata trichome development vary depending on the organ where they are formed. Stem, leaf and pedicel trichomes recruit most of the transcription factors (TFs) described above. Conversely, floral trichomes only use a small subset of genes including AfimGL2, AfimRAV1-like, AfimWIN1, AfimMYB106-like and AfimHDG2. The remaining TFs, AfimTTG1, AfimGL3, AfimTRY, AfimMYB5 and AfimMYB6, are restricted to the abaxial (outer) and the adaxial (inner) pavement epidermal cells. CONCLUSIONS: We re-evaluate the core genetic network shaping trichome fate in flowers of an early-divergent angiosperm lineage and show a morphologically diverse output with a simpler genetic mechanism in place when compared to the models Arabidopsis thaliana and Cucumis sativus. In turn, our results strongly suggest that the canonical trichome gene expression appears to be more conserved in vegetative than in floral tissues across angiosperms.

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PREMISE OF THE STUDY: Bilateral symmetry in core eudicot flowers is established by the differential expression of CYCLOIDEA (CYC), DICHOTOMA (DICH), and RADIALIS (RAD), which are restricted to the dorsal portion of the flower, and DIVARICATA (DIV), restricted to the ventral and lateral petals. Little is known regarding the evolution of these gene lineages in non-core eudicots, and there are no reports on gene expression that can be used to assess whether the network predates the diversification of core eudicots. METHODS: Homologs of the RAD and DIV lineages were isolated from available genomes and transcriptomes, including those of three selected non-core eudicot species, the magnoliid Aristolochia fimbriata and the monocots Cattleya trianae and Hypoxis decumbens. Phylogenetic analyses for each gene lineage were performed. RT-PCR was used to evaluate the expression and putative contribution to floral symmetry in dissected floral organs of the selected species. KEY RESULTS: RAD-like genes have undergone at least two duplication events before eudicot diversification, three before monocots and at least four in Orchidaceae. DIV-like genes also duplicated twice before eudicot diversification and underwent independent duplications specific to Orchidaceae. RAD-like and DIV-like genes have differential dorsiventral expression only in C. trianae, which contrasts with the homogeneous expression in the perianth of A. fimbriata. CONCLUSIONS: Our results point to a common genetic regulatory network for floral symmetry in monocots and core eudicots, while alternative genetic mechanisms are likely driving the bilateral perianth symmetry in the early-diverging angiosperm Aristolochia.

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The perianth organs of six species of Nymphaeaceae, representing Euryale, Nymphaea and Victoria, were studied on the basis of macroscopical, micromorphological, and anatomical characters. The aims were to determine whether perianth is differentiated among tepal whorls considering the presence of sepaloid and petaloid characters, and to evaluate the occurrence of both features in individual tepals. Selected perianth series were examined macroscopically, with light microscopy, and scanning electron microscopy. Osmophores were detected using neutral red and Sudan. In all tepals examined, stomata and hydropotes were present on the abaxial and adaxial surfaces. These are anomocytic or stephanocytic; hydropotes of irregular type are also present. The outer series of tepals display morpho-anatomical characters in most part related with photosynthetic and protective functions. Osmophore activity is very scarce and petaloid epidermal morphology is present only in N. lotus, thus allowing interpretation of this whorl as primarily sepaloid. The second series exhibits both petal-like and sepal-like characters; in N. amazonum and N. gardneriana sepaloid and petaloid group of cells are present on the abaxial surface of individual tepals. Therefore, this whorl is transitional between the outer and the innermost ones. Both the morpho-anatomy and presence of osmophore activity indicate that the innermost series is entirely petaloid. Inner tepals of E. ferox, N. alba, and V. cruziana share the presence of epidermal cells with predominantly smooth cuticle, whereas those of N. amazonum, N. gardneriana, and N. lotus share a cuticular ornamentation consisting of numerous papillae on each cell. Morphological characters of the perianth epidermis are in some respects congruent with the molecular phylogeny of Nymphaeaceae. Our results support the co-expression of sepaloidy and petaloidy within individual tepals and the mosaic model of perianth evolution proposed for the angiosperms.

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The morphology and structure of the flowers and fruits of Chamissoa altissima (Jacq.) Kunth during the development were analyzed. The plant material was fixed in FAA 50, embedded in historesin and sectioned according to standard techniques. The flowers presented tepals with betalain and homogeneous mesophyll; receptacular nectary; anthers with epidermis, endothecium, one middle layer, and uninucleate tapetum; and monocarpelar ovary with homogeneous mesophyll. The fruit was a circumscissile capsule, presented the same number of cellular layers that the ovary, and possessed subendocarpic sclerenchyma. The seed was bitegmic, exotestal and perispermic.

Chamissoa altissima (Jacq.) Kunth ocorre em remanescentes florestais de Maringá, Paraná, Brasil e se destaca por seus frutos zoocóricos envolvidos por sépalas vermelhas. As flores e frutos em diferentes fases de desenvolvimento são descritos estruturalmente. O material botânico foi fixado em FAA 50, emblocado em historresina e secionado conforme técnicas usuais. As flores apresentam sépalas com betalaína e mesofilo homogêneo; nectário receptacular; anteras com epiderme, endotécio, uma camada média e tapete uninucleado; e ovário monocarpelar com mesofilo homogêneo. O fruto é uma cápsula circuncisa, apresenta o mesmo número de camadas celulares que o ovário, e possui esclerênquima subendocárpico. A semente é bitegumentada, exotestal e perispérmica.

RESUMO

This study analyzed the morphology and anatomy of the Cordia trichotoma (Vell.) Arrab. ex I. M. Johnst diaspore. The objectives were: the structural analysis of the calyx and corolla that persisted in the ripe fruit and acted in the anemocoric dispersion process; the vascularization of the gynoecium for better understanding of the carpel/locule number of the ovary; nectary structure; and the anatomical analysis of the developmental pericarp and seed for better definition of the fruit type. The results showed that the perianth had aerenchyma and the ovary was 2- 4- locule forming endothelium and false septum. The fruit was drupoid nuculanium and the seed was exotestal.

Esse estudo analisa a morfologia e anatomia do diásporo de Cordia trichotoma (Vell.) Arrab. ex I. M. Johnst. Os objetivos do estudo são: a análise estrutural do cálice e corola que persistem no fruto maduro e atuam no processo de dispersão anemocórica; a vascularização do gineceu para melhor entendimento do número de carpelos/lóculos do ovário; a estrutura do nectário; e a análise anatômica do pericarpo e semente em desenvolvimento, para melhor definição do tipo de fruto. O perianto tem aerênquima. O ovário tem 2 e 4 lóculos e forma endotélio e septo falso. O fruto é drupóide nuculânio e a semente é exotestal.