Flower Defects Research Articles

Transcriptomic and lipidomic profiles of glycerolipids during Arabidopsis flower development

Flower glycerolipids are the yet-to-be discovered frontier of the lipidome. Although ample evidence suggests important roles for glycerolipids in flower development, stage-specific lipid profiling in tiny Arabidopsis flowers is challenging. Here, we utilized a transgenic system to synchronize flower development in Arabidopsis. The transgenic plant PAP1::AP1-GR ap1-1 cal-5 showed synchronized flower development upon dexamethasone treatment, which enabled massive harvesting of floral samples of homogenous developmental stages for glycerolipid profiling. Glycerolipid profiling revealed a decrease in concentrations of phospholipids involved in signaling during the early development stages, such as phosphatidic acid and phosphatidylinositol, and a marked increase in concentrations of nonphosphorous galactolipids during the late stage. Moreover, in the midstage, phosphatidylinositol 4,5-bisphosphate concentration was increased transiently, which suggests the stimulation of the phosphoinositide metabolism. Accompanying transcriptomic profiling of relevant glycerolipid metabolic genes revealed simultaneous induction of multiple phosphoinositide biosynthetic genes associated with the increased phosphatidylinositol 4,5-bisphosphate concentration, with a high degree of differential expression patterns for genes encoding other glycerolipid-metabolic genes. The phosphatidic acid phosphatase mutant pah1 pah2 showed flower developmental defect, suggesting a role for phosphatidic acid in flower development. Our concurrent profiling of glycerolipids and relevant metabolic gene expression revealed distinct metabolic pathways stimulated at different stages of flower development in Arabidopsis.

Molecular characterization and functional analysis of a Flowering locus T homolog gene from a Phalaenopsis orchid.

Warm day and cool night conditions significantly induce reproductive spike formation in Phalaenopsis plants; hence, determining the flowering mechanism regulating the reproductive transition is important. Flowering locus T (FT) plays important roles in flowering induction in several plants. To explore spike induction by warm days and cool nights in Phalaenopsis orchids, we isolated the FT (PhFT) from Phalaenopsis hybrid Fortune Saltzman. The cDNA of PhFT was 809-bp long and contained a 531-bp open reading frame encoding a putative protein of 176 amino acids, a 58-bp 5'-untranslated region (UTR), and a 220-bp 3'-UTR. The predicted molecular mass of PhFT was 19.80 kDa, with an isoelectric point of 8.68. The PhFT was predicted to possess the conserved functional regions of the phosphatidylethanolamine-binding protein superfamily. Nucleotide sequence data indicated that PhFT contained 3 introns and 4 exons. Sequence alignment and phylogenetic analyses of PhFT revealed high homology to the FT proteins of Cymbidium goeringii and Oncidium Gower Ramsey. Quantitative real-time polymerase chain reaction analysis indicated that PhFT mRNA was expressed in roots, apical leaves, mature leaves, and flowers. In flowers, PhFT was expressed more in developing floral buds than in mature flowers and was predominantly expressed in ovaries and petals. Ectopic expression of PhFT in Arabidopsis ft-1 mutants showed novel early-flowering phenotypes that lost their siliques. Our results indicated that the ectopic expression of PhFT could partially complement the late flowering defect in transgenic Arabidopsis ft-1 mutants. Our findings suggest that PhFT is a putative FT homolog in Phalaenopsis plants that regulates flowering transition.

Defects in bilayer silica and graphene: common trends in diverse hexagonal two-dimensional systems.

By combining first-principles and classical force field calculations with aberration-corrected high-resolution transmission electron microscopy experiments, we study the morphology and energetics of point and extended defects in hexagonal bilayer silica and make comparison to graphene, another two-dimensional (2D) system with hexagonal symmetry. We show that the motifs of isolated point defects in these 2D structures with otherwise very different properties are similar, and include Stone-Wales-type defects formed by structural unit rotations, flower defects and reconstructed double vacancies. The morphology and energetics of extended defects, such as grain boundaries have much in common as well. As both sp2-hybridised carbon and bilayer silica can also form amorphous structures, our results indicate that the morphology of imperfect 2D honeycomb lattices is largely governed by the underlying symmetry of the lattice.

Regulation of floral patterning and organ identity by Arabidopsis ERECTA-family receptor kinase genes

Due to the lack of cell migration, plant organogenesis relies on coordinated cell proliferation, cell growth, and differentiation. A flower possesses a complex structure, with sepals and petals constituting the perianth, and stamens and pistils where male and female gametophytes differentiate. While advances have been made in our understanding of gene regulatory networks controlling flower development, relatively little is known of how cell-cell coordination influences floral organ specification. The Arabidopsis ERECTA (ER)-family receptor kinases, ER, ER-LIKE1 (ERL1), and ERL2, regulate inflorescence architecture, organ shape, and epidermal stomatal patterning. Here it is reported that ER-family genes together regulate floral meristem organization and floral organ identity. The stem cell marker CLAVATA3 exhibits misplaced expression in the floral meristems of the er erl1 erl2 mutant. Strikingly, homeotic conversion of sepals to carpels was observed in er erl1 erl2 flowers. Consistently, ectopic expression of AGAMOUS, which determines carpel identity, was detected in er erl1 erl2 flower primordia. Among the known downstream components of ER-family receptor kinases in stomatal patterning, YODA (YDA) is also required for proper floral patterning. YDA and the ER-family show complex, synergistic genetic interactions: er erl1 erl2 yda quadruple mutant plants become extremely small, callus-like masses. While a constitutively active YDA fully rescues stomatal clustering in er erl1 erl2, it only partially rescues er erl1 erl2 flower defects. The study suggests that ER-family signalling is crucial for ensuring proper expression domains of floral meristem and floral organ identity determinants, and further implies the existence of a non-canonical downstream pathway.

The Over-Expression of an Arabidopsis B3 Transcription Factor, ABS2/NGAL1, Leads to the Loss of Flower Petals

Transcriptional regulations are involved in many aspects of plant development and are mainly achieved through the actions of transcription factors (TF). To investigate the mechanisms of plant development, we carried out genetic screens for mutants with abnormal shoot development. Taking an activation tagging approach, we isolated a gain-of-function mutant abs2-1D (abnormal shoot 2-1D). abs2-1D showed pleiotropic growth defects at both the vegetative and reproductive developmental stages. We cloned ABS2 and it encodes a RAV sub-family of plant B3 type of transcriptional factors. Phylogenetic analysis showed that ABS2 was closely related to NGATHA (NGA) genes that are involved in flower development and was previously named NGATHA-Like 1 (NGAL1). NGAL1 was expressed mainly in the root and the filament of the stamen in flower tissues and sub-cellular localization assay revealed that NGAL1 accumulated in the nucleus. Interestingly, over-expression of NGAL1 driven by the constitutive 35S promoter led to transgenic plants with conspicuous flower defects, particularly a loss-of-petal phenotype. A loss-of-function ngal1-1 mutant did not show obvious phenotype, suggesting the existence of redundant activities and also the utility of gain-of-function genetic screens. Our results show that the over-expression of NGAL1 is capable of altering flower petal development, as well as shoot development.

A nucleostemin-like GTPase required for normal apical and floral meristem development inArabidopsis

Mammalian nucleostemin (NS) is preferentially expressed in stem cells and acts to promote cell cycle progression. In plants, stem cell activities have to be terminated during flower development, and this process requires the activation of AGAMOUS (AG) gene expression. Here, a nucleostemin-like 1 gene, NSN1, is shown to be required for flower development in Arabidopsis. The NSN1 mRNA was found in the inflorescence meristem and floral primordia, and its protein was localized to the nucleoli. Both heterozygous and homozygous plants developed defective flowers on inflorescences that were eventually terminated by the formation of carpelloid flowers. Overexpression of NSN1 resulted in loss of apical dominance and formation of defective flowers. Expression of the AG gene was found to be up-regulated in nsn1. The carpelloid flower defect of nsn1 was suppressed by the ag mutation in the nsn1 ag double mutant, whereas double mutants of nsn1 apetala2 (ap2) displayed enhanced defective floral phenotypes. These results suggest that in the delicately balanced regulatory network, NSN1 acts to repress AG and plays an additive role with AP2 in floral organ specification. As a midsize nucleolar GTPase, NSN1 represents a new class of regulatory proteins required for flower development in Arabidopsis.

Grain boundary loops in graphene

Topological defects can affect the physical properties of graphene in unexpected ways. Harnessing their influence may lead to enhanced control of both material strength and electrical properties. Here we present a new class of topological defects in graphene composed of a rotating sequence of dislocations that close on themselves, forming grain boundary loops that either conserve the number of atoms in the hexagonal lattice or accommodate vacancy/interstitial reconstruction, while leaving no unsatisfied bonds. One grain boundary loop is observed as a "flower" pattern in scanning tunneling microscopy (STM) studies of epitaxial graphene grown on SiC(0001). We show that the flower defect has the lowest energy per dislocation core of any known topological defect in graphene, providing a natural explanation for its growth via the coalescence of mobile dislocations.

Functional Analysis of FT and TFL1 Orthologs from Orchid (Oncidium Gower Ramsey) that Regulate the Vegetative to Reproductive Transition

The FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1 (TFL1) genes play crucial roles in regulating the vegetative to reproductive phase transition. Orthologs of FT/TFL1 (OnFT and OnTFL1) were isolated and characterized from Oncidium Gower Ramsey. OnFT mRNA was detected in axillary buds, leaves, pseudobulb and flowers. In flowers, OnFT was expressed more in young flower buds than in mature flowers and was predominantly expressed in sepals and petals. The expression of OnFT was regulated by photoperiod, with the highest expression from the 8th to 12th hour of the light period and the lowest expression at dawn. In contrast, the expression of OnTFL1 was only detected in axillary bud and pseudobulb, and was not influenced by light. Ectopic expression of OnFT in transgenic Arabidopsis plants showed novel phenotypes by flowering early and losing inflorescence indeterminacy. In addition, ectopic expression of OnFT was able to partially complement the late flowering defect in transgenic Arabidopsis ft-1 mutants. In transgenic tfl1-11 mutant plants, 35S::OnTFL1 delayed flowering and rescued the phenotype of terminal flowers. Furthermore, substitution of the key single amino acid His85 by Tyr was able to convert the OnTFL1 function to OnFT by promoting flowering in 35S::OnTFL1-H85Y transgenic Arabidopsis plants. Further analysis indicated that the expression of APETALA1 (AP1) was significantly up-regulated in 35S::OnFT and 35S::OnTFL1-H85Y plants, and was down-regulated in 35S::OnTFL1 transgenic Arabidopsis plants. Our data indicated that OnFT and OnTFL1 are putative phosphatidylethanolamine-binding protein genes in orchids that regulate flower transition similar to their orthologs in Arabidopsis.

Histone H2B monoubiquitination in the chromatin of FLOWERING LOCUS C regulates flowering time in Arabidopsis.

Ubiquitination is one of many known histone modifications that regulate gene expression. Here, we examine the Arabidopsis thaliana homologs of the yeast E2 and E3 enzymes responsible for H2B monoubiquitination (H2Bub1). Arabidopsis has two E3 homologs (HISTONE MONOUBIQUITINATION1 [HUB1] and HUB2) and three E2 homologs (UBIQUITIN CARRIER PROTEIN [UBC1] to UBC3). hub1 and hub2 mutants show the loss of H2Bub1 and early flowering. By contrast, single ubc1, ubc2, or ubc3 mutants show no flowering defect; only ubc1 ubc2 double mutants, and not double mutants with ubc3, show early flowering and H2Bub1 defects. This suggests that ubc1 and ubc2 are redundant, but ubc3 is not involved in flowering time regulation. Protein interaction analysis showed that HUB1 and HUB2 interact with each other and with UBC1 and UBC2, as well as self-associating. The expression of FLOWERING LOCUS C (FLC) and its homologs was repressed in hub1, hub2, and ubc1 ubc2 mutant plants. Association of H2Bub1 with the chromatin of FLC clade genes depended on UBC1,2 and HUB1,2, as did the dynamics of methylated histones H3K4me3 and H3K36me2. The monoubiquitination of H2B via UBC1,2 and HUB1,2 represents a novel form of histone modification that is involved in flowering time regulation.

Functional Analysis of Three Lily (Lilium longiflorum) APETALA1-like MADS Box Genes in Regulating Floral Transition and Formation

Three cDNAs showing a high degree of homology to the SQUA subfamily of MADS box genes were isolated and characterized from the lily (Lilium longiflorum). Lily MADS Box Gene 5 (LMADS5) showed high sequence identity to oil palm (Elaeis guineensis) SQUAMOSA3 (EgSQUA3). LMADS6 is closely related to LMADS5 whereas LMADS7 is more related to DOMADS2, an orchid (Dendrobium) gene in the SQUA subfamily. The expression pattern for these three genes was similar and their RNAs were detected in vegetative stem and inflorescence meristem. LMADS5 and 6 were highly expressed in vegetative leaves and carpel, whereas LMADS7 expression was absent. Ectopic expression of LMADS5, 6 or 7 in transgenic Arabidopsis plants showed novel phenotypes by flowering early and producing terminal flowers. Homeotic conversions of sepals to carpelloid structures and of petal to stamen-like structures were also observed in 35S::LMADS5, 6 or 7 flowers. Ectopic expression of LMADS6 or LMADS7 was able to complement the ap1 flower defect in transgenic Arabidopsis ap1 mutant plants. These results strongly indicated that the function of these three lily genes was involved in flower formation as well as in floral induction. Furthermore, the ability of lily LMADS6 and 7 to complement the Arabidopsis ap1 mutant provided further evidence to show that the conserved motifs (paleoAP1 or euAP1) in the C-terminus of the SQUA/AP1 subfamily of MADS box genes is not strictly necessary for their function.

Characterization of 8-in. wafers printed by nanoimprint lithography

Nanoimprint lithography is a promising technique which should allow good lithography to be achieved on a large surface in a short time and by a relatively simple process. Printing processes have been already demonstrated on 6-in. wafers with a few patterns distributed across the surface. In this paper, results of fully printed 8-in. wafers are presented; it is shown that patterns in the size range of 250 nm–100 μm can be obtained by one printing step on this large surface. The defects which can appear in the polymer during the nanoimprint lithography process are studied. The defect types depend on some printing conditions: air, vacuum, residual solvent. It is demonstrated that some defects are due to Saffman–Taylor instabilities, and that capillary strengths and mold deformation are responsible for the flower defects.

Characterization of 8-in. wafers printed by nanoimprint lithography

Nanoimprint lithography is a promising technique which should allow good lithography to be achieved on a large surface in a short time and by a relatively simple process. Printing processes have been already demonstrated on 6-in. wafers with a few patterns distributed across the surface. In this paper, results of fully printed 8-in. wafers are presented; it is shown that patterns in the size range of 250 nm–100 μm can be obtained by one printing step on this large surface. The defects which can appear in the polymer during the nanoimprint lithography process are studied. The defect types depend on some printing conditions: air, vacuum, residual solvent. It is demonstrated that some defects are due to Saffman–Taylor instabilities, and that capillary strengths and mold deformation are responsible for the flower defects.

Blocking histone deacetylation in Arabidopsis induces pleiotropic effects on plant gene regulation and development

Histone acetylation and deacetylation play essential roles in eukaryotic gene regulation. Reversible modifications of core histones are catalyzed by two intrinsic enzymes, histone acetyltransferase and histone deacetylase (HD). In general, histone deacetylation is related to transcriptional gene silencing, whereas acetylation correlates with gene activation. We produced transgenic plants expressing the antisense Arabidopsis HD (AtHD1) gene. AtHD1 is a homolog of human HD1 and RPD3 global transcriptional regulator in yeast. Expression of the antisense AtHD1 caused dramatic reduction in endogenous AtHD1 transcription, resulting in accumulation of acetylated histones, notably tetraacetylated H4. Reduction in AtHD1 expression and AtHD1 production and changes in acetylation profiles were associated with various developmental abnormalities, including early senescence, ectopic expression of silenced genes, suppression of apical dominance, homeotic changes, heterochronic shift toward juvenility, flower defects, and male and female sterility. Some of the phenotypes could be attributed to ectopic expression of tissue-specific genes (e.g., SUPERMAN) in vegetative tissues. No changes in genomic DNA methylation were detected in the transgenic plants. These results suggest that AtHD1 is a global regulator, which controls gene expression during development through DNA-sequence independent or epigenetic mechanisms in plants. In addition to DNA methylation, histone modifications may be involved in a general regulatory mechanism responsible for plant plasticity and variation in nature.

Blocking histone deacetylation in Arabidopsis induces pleiotropic effects on plant gene regulation and development.

Histone acetylation and deacetylation play essential roles in eukaryotic gene regulation. Reversible modifications of core histones are catalyzed by two intrinsic enzymes, histone acetyltransferase and histone deacetylase (HD). In general, histone deacetylation is related to transcriptional gene silencing, whereas acetylation correlates with gene activation. We produced transgenic plants expressing the antisense Arabidopsis HD (AtHD1) gene. AtHD1 is a homolog of human HD1 and RPD3 global transcriptional regulator in yeast. Expression of the antisense AtHD1 caused dramatic reduction in endogenous AtHD1 transcription, resulting in accumulation of acetylated histones, notably tetraacetylated H4. Reduction in AtHD1 expression and AtHD1 production and changes in acetylation profiles were associated with various developmental abnormalities, including early senescence, ectopic expression of silenced genes, suppression of apical dominance, homeotic changes, heterochronic shift toward juvenility, flower defects, and male and female sterility. Some of the phenotypes could be attributed to ectopic expression of tissue-specific genes (e.g., SUPERMAN) in vegetative tissues. No changes in genomic DNA methylation were detected in the transgenic plants. These results suggest that AtHD1 is a global regulator, which controls gene expression during development through DNA-sequence independent or epigenetic mechanisms in plants. In addition to DNA methylation, histone modifications may be involved in a general regulatory mechanism responsible for plant plasticity and variation in nature.