2,284 research outputs found
Usual and unusual development of the dicot leaf: Involvement of transcription factors and hormones
No full textMorphological diversity exhibited by higher plants is essentially related to the tremendous variation of leaf shape. With few exceptions, leaf primordia are initiated postembryonically at the flanks of a group of undifferentiated and proliferative cells within the shoot apical meristem (SAM) in characteristic position for the species and in a regular phyllotactic sequence. Auxin is critical for this process, because genes involved in auxin biosynthesis, transport, and signaling are required for leaf initiation. Down-regulation of transcription factors (TFs) and cytokinins are also involved in the light-dependent leaf initiation pathway. Furthermore, mechanical stresses in SAM determine the direction of cell division and profoundly influence leaf initiation suggesting a link between physical forces, gene regulatory networks and biochemical gradients. After the leaf is initiated, its further growth depends on cell division and cell expansion. Temporal and spatial regulation of these processes determines the size and the shape of the leaf, as well as the internal structure. A complex array of intrinsic signals, including phytohormones and TFs control the appropriate cell proliferation and differentiation to elaborate the final shape and complexity of the leaf. Here, we highlight the main determinants involved in leaf initiation, epidermal patterning, and elaboration of lamina shape to generate small marginal serrations, more deep lobes or a dissected compound leaf. We also outline recent advances in our knowledge of regulatory networks involved with the unusual pattern of leaf development in epiphyllous plants as well as leaf morphology aberrations, such as galls after pathogenic attacks of pests
CYCLOIDEA 2 Clade Genes: Key Players in the Control of Floral Symmetry, Inflorescence Architecture, and Reproductive Organ Development
No full textUndoubted lines of evidence point out that members of CYCLOIDEA (CYC) 2 clade are essential players to control flower symmetry and, amusingly, also are determinants of capitula architecture (pseudanthium). In several species, CYC-like genes influence the androecium patterning, but to date, the function of these genes in the development of gynoecium organs is less clear. In this review, we first reported details about floral symmetry and an overview of genes and molecular mechanisms regulating the development of zygomorphism in different angiosperm lineages (e.g., basal and core eudicots and monocots). Then, we paid emphasis on the role of CYC-like genes in the development of heterogamous inflorescence of sunflower as well as other Asteraceae and some species within the Dipsacaceae family. Helianthus annuus is particularly attractive because it represents a useful model to study the role of CYC-like genes on shaping floral corolla as well as the differentiation of reproductive organs in different flowers of pseudanthia. A special attention was reserved to inflorescence morphology mutants of sunflower (i.e., Chrysanthemoids2 and tubular ray flower) because they provide useful information on the role of CYC-like genes in the radiate capitulum evolution. Finally, we discuss data from literature to suggest that CYC-like genes are also co-opted to regulate stamen and carpel differentiation likely throughout their interaction with the cell cycle and flower organ identity genes. The recruitment of reproductive organs in ray flowers also supports the phylogenetic origin of a radiate inflorescence of sunflower from a discoid capitulum and suggests that in sterile zygomorphic ray flower primordia the latent identity to differentiate both microsporangium and macrosporangium was conserved
Mobilization of the Tetu1 transposable element of Helianthus annuus: evidence for excision in different developmental stages
No full textThe tubular ray flower (turf) mutant of sunflower is characterized by a switch of ray flowers from zygomorphic to near-actinomorphic disc flowers. In sunflower, floral symmetry of ray and disc flowers is specified by the activity of members of a CYCLOIDEA (CYC) gene family. The turf mutant is generated by the insertion of a CACTA-like transposable element (TE), named Transposable element of turf1 (Tetu1), in the coding sequence of the HaCYC2c gene. The TEinsertion changes the reading frame of turf-HaCYC2c for the encoded protein and leads to a premature stop codon. Tetu1 is a non-autonomous version of a CACTA TEcarrying the minimum sequences necessary for transposition in the presence of autonomous elements in the sunflower genome. In the previous analysis, performed in more than 11 000 plants homozygous for the turf-HaCYC2c allele, the absence of chimerism and the segregation rate of derived-progenies from reverted phenotypes suggest that Tetu1 transpositions are restricted to a time shortly before and/or during meiosis. Here, we report the analysis of F5 and F6 progenies, derived from an F4 progeny of the cross turf × Chrysanthemoides2, where plants with a chimeric inflorescence were detected. Tetu1 showed active excision in all progenies taken into consideration and named High Frequency of Tetu1 Transposition (HFTT). Within a total of 449 plants, Tetu1 excision generated a 13.81 % of non-chimeric revertants but also a 5.12 % of plants with somatic sectors of variable size in the outmost whorl of the inflorescence. These unexpected results suggest variations in tissue specificity and time of TEexcision. The excision of Tetu1 was confirmed by DNA molecular screening of non-chimeric and chimeric revertants and transcription analysis of the HaCYC2c gene. In HFTT progenies, sequence analyses excluded significant DNA changes with respect to the original Tetu1 transposon as well as to the adjacent 5’- and 3’-TE regions. Genetic and epigenetic regulatory mechanisms were proposed to explain the time and frequency of Tetu1 transposition in HFTT progenies
Induction of Somatic Embryogenesis in Plants: Different Players and Focus on WUSCHEL and WUS-RELATED HOMEOBOX (WOX) Transcription Factors
No full textIn plants, other cells can express totipotency in addition to the zygote, thus resulting in embryo differentiation; this appears evident in apomictic and epiphyllous plants. According to Haberlandt’s theory, all plant cells can regenerate a complete plant if the nucleus and the membrane system are intact. In fact, under in vitro conditions, ectopic embryos and adventitious shoots can develop from many organs of the mature plant body. We are beginning to understand how determination processes are regulated and how cell specialization occurs. However, we still need to unravel the mechanisms whereby a cell interprets its position, decides its fate, and communicates it to others. The induction of somatic embryogenesis might be based on a plant growth regulator signal (auxin) to determine an appropriate cellular environment and other factors, including stress and ectopic expression of embryo or meristem identity transcription factors (TFs). Still, we are far from having a complete view of the regulatory genes, their target genes, and their action hierarchy. As in animals, epigenetic reprogramming also plays an essential role in re-establishing the competence of differentiated cells to undergo somatic embryogenesis. Herein, we describe the functions of WUSCHEL-RELATED HOMEOBOX (WOX) transcription factors in regulating the differentiation–dedifferentiation cell process and in the developmental phase of in vitro regenerated adventitious structures
The vascular plants: open system of growth
No full textWhat is fascinating in plants (true also in sessile animals such as corals and hydroids) is definitely their open and indeterminate growth, as a result of meristematic activity. Plants as well as animals are characterized by a multicellular organization, with which they share a common set of genes inherited from a common eukaryotic ancestor; nevertheless, circa 1.5 billion years of evolutionary history made the two kingdoms very different in their own developmental biology. Flowering plants, also known as angiosperms, arose during the Cretaceous Period (145–65 million years ago), and up to date, they count around 235,000 species, representing the largest and most diverse group within the plant kingdom. One of the foundations of their success relies on the plant–pollinator relationship, essentially unique to angiosperms that pushed large speciation in both plants and insects and on the presence of the carpel, the structure devoted to seed enclosure. A seed represents the main organ preserving the genetic information of a plant; during embryogenesis, the primary axis of development is established by two groups of pluripotent cells: the shoot apical meristem (SAM), responsible for gene rating all aboveground organs, and the root apical meristem (RAM), responsible for producing all underground organs. During postembryonic shoot development, axillary meristem (AM) initiation and outgrowth are responsible for producing all secondary axes of growth including inflorescence branches or flowers. The production of AMs is tightly linked to the production of leaves and their separation from SAM. As leaf primordia are formed on the flanks of the SAM, a region between the apex and the developing organ is established and referred to as boundary zone. Interaction between hormones and the gene network in the boundary zone is fundamental for AM initiation. AMs only develop at the adaxial base of the leaf; thus, AM initiation is also strictly associated with leaf polarity. AMs function as new SAMs: form axillary buds with a few leaves and then the buds can either stay dormant or develop into shoot branches to define a plant architecture, which in turn affects assimilate production and reproductive efficiency. Therefore, the radiation of angiosperms was accompanied by a huge diversification in growth forms that determine an enormous morphological plasticity helping plants to environmental changes. In this review, we focused on the developmental processes of AM initiation and outgrowth. In particular, we summarized the primary growth of SAM, the key role of positional signals for AM initiation, and the dissection of molecular players involved in AM initiation and outgrowth. Finally, the interaction between phytohormone signals and gene regulatory network controlling AM development was discussed
Orange, yellow and white-cream: inheritance of carotenoid-based colour of sunflower pollen
No full textMolecular cloning and expression profile analysis of three sunflower (Helianthus annuus) diterpene synthase genes.
No full textent-Kaurene, a key precursor of gibberellins, is formed by the action of two diterpene synthases (diTPSs), ent-copalyl diphosphate synthase (CPS), and ent-kaurene synthase (KS). The full-length cDNAs of CPS- (HaCPS1L) and KS-like (HaKS2L and HaKS3L) genes were isolated from sunflower. The amino acid sequences of HaCPS1L, HaKS2L, and HaKS3L exhibit structural features and homology to diTPSs of several plant species involved in gibberellin biosynthesis. RT-PCR analysis indicates that the expression of all genes (HaCPS1L, HaKS2L, and HaKS3L) is highly regulated during growth and development. All three diTPSs are preferentially expressed in rapidly growing tissues. HaKS2L is expressed at a much lower level than the other two diTPS genes. During seed development, the high level of both HaCPS1L and HaKS3L transcripts correlated with the period of rapid growth of the embryo. The three diTPS genes are not subjected to feedback regulation by gibberellin activit
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