David TWELL
University of Leicester, Biology, Faculty Member
In plant cells, mitochondria and plastids contain their own genomes derived from the ancestral bacteria endosymbiont. Despite their limited genetic capacity, these multicopy organelle genomes account for a substantial fraction of total... more
In plant cells, mitochondria and plastids contain their own genomes derived from the ancestral bacteria endosymbiont. Despite their limited genetic capacity, these multicopy organelle genomes account for a substantial fraction of total cellular DNA, raising the question of whether organelle DNA quantity is controlled spatially or temporally. In this study, we genetically dissected the organelle DNA decrease in pollen, a phenomenon that appears to be common in most angiosperm species. By staining mature pollen grains with fluorescent DNA dye, we screened Arabidopsis thaliana for mutants in which extrachromosomal DNAs had accumulated. Such a recessive mutant, termed defective in pollen organelle DNA degradation1 (dpd1), showing elevated levels of DNAs in both plastids and mitochondria, was isolated and characterized. DPD1 encodes a protein belonging to the exonuclease family, whose homologs appear to be found in angiosperms. Indeed, DPD1 has Mg2+-dependent exonuclease activity when expressed as a fusion protein and when assayed in vitro and is highly active in developing pollen. Consistent with the dpd phenotype, DPD1 is dual-targeted to plastids and mitochondria. Therefore, we provide evidence of active organelle DNA degradation in the angiosperm male gametophyte, primarily independent of maternal inheritance; the biological function of organellar DNA degradation in pollen is currently unclear.
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Reproduction, Biology, Medicine, Biological Sciences, Plant Physiology, and 14 morePollen, Plant, mRNA stability, Luciferase, POLLEN GERMINATION, Base Sequence, Pollen Tube Growth, PLANT PROTEINS, Nucleic Acid Conformation, Protein Biosynthesis, Pollen tube, Gene expression profiling, Molecular Sequence Data, and Reporter gene
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<b>Copyright information:</b>Taken from "MADS-complexes regulate transcriptome dynamics during pollen maturation"http://genomebiology.com/content/8/11/R249Genome Biology 2007;8(11):R249-R249.Published online 22 Nov... more
<b>Copyright information:</b>Taken from "MADS-complexes regulate transcriptome dynamics during pollen maturation"http://genomebiology.com/content/8/11/R249Genome Biology 2007;8(11):R249-R249.Published online 22 Nov 2007PMCID:PMC2258202. Of the genes downregulated in //triple mutant pollen, 83.4% exhibit peak expression at the mature pollen grain (MPG) stage of wild-type (WT) pollen development (according to Honys and Twell [11]), whereas 56.7% of the genes upregulated in this mutant peak during the immature tricellular stage (tricellular pollen [TCP]). In total, 83.5% of the upregulated genes peak during the three immature stages (unicellular microspores [UNM], BCP, and TCP). The AtMIKC* complexes contribute quite significantly to the transcriptional changes that occur during pollen maturation. We ranked all genes that were consistently called present in WT pollen according to their expression level in mature WT pollen, in descending order (the highest expressed gene received number 1). In this graph the ranking numbers of all genes upregulated and downregulated in triple mutant pollen are plotted, revealing that AtMIKC* complexes predominantly activate high-abundance and medium-abundance transcripts, while repressing low-abundance and medium-abundance transcripts. All calculations related to these graphs are included in Additional data file 2.
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We successfully cloned the full cDNA sequence of OsDUO1(Oryza sativa duo pollen 1) encoding a putative R2R3 type MYB transcription factor by RT-PCR.The OsDUO1 cDNA is 1 032 bp in length and encodes a protein with 343 amino acids.The... more
We successfully cloned the full cDNA sequence of OsDUO1(Oryza sativa duo pollen 1) encoding a putative R2R3 type MYB transcription factor by RT-PCR.The OsDUO1 cDNA is 1 032 bp in length and encodes a protein with 343 amino acids.The expression of OsDUO1 was detectable only during the late pollen development in rice,suggesting the possible biological function of OsDUO1 during late rice pollen development.Bioinformatics analysis showed that OsDUO1 has close homologs in Brachypodium distachyon,Sorghum bicolor,Zea mays,Arabidopsis thaliana,Nicotiana tabacum,Vitis vinifera,Ricinus communis,Populus trichocarpa and Physcomitrella patens suggesting the conserved function of OsDUO1 in plants during evolution.
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ABSTRACT
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SummaryThe conserved Fused kinase plays vital but divergent roles in many organisms from Hedgehog signalling in Drosophila to polarization and chemotaxis in Dictyostelium. Previously we have shown that Arabidopsis Fused kinase termed... more
SummaryThe conserved Fused kinase plays vital but divergent roles in many organisms from Hedgehog signalling in Drosophila to polarization and chemotaxis in Dictyostelium. Previously we have shown that Arabidopsis Fused kinase termed TWO‐IN‐ONE (TIO) is essential for cytokinesis in both sporophytic and gametophytic cell types. Here using in vivo imaging of GFP‐tagged microtubules in dividing microspores we show that TIO is required for expansion of the phragmoplast. We identify the phragmoplast‐associated kinesins, PAKRP1/Kinesin‐12A and PAKRP1L/Kinesin‐12B, as TIO‐interacting proteins and determine TIO‐Kinesin‐12 interaction domains and their requirement in male gametophytic cytokinesis. Our results support the role of TIO as a functional protein kinase that interacts with Kinesin‐12 subfamily members mainly through the C‐terminal ARM repeat domain, but with a contribution from the N‐terminal kinase domain. The interaction of TIO with Kinesin proteins and the functional requirement of their interaction domains support the operation of a Fused kinase signalling module in phragmoplast expansion that depends upon conserved structural features in diverse Fused kinases.
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Glycosylphosphatidylinositol (GPI) anchoring provides an alternative to transmembrane domains for anchoring proteins to the cell surface in eukaryotes. GPI anchors are synthesized in the endoplasmic reticulum via the sequential addition... more
Glycosylphosphatidylinositol (GPI) anchoring provides an alternative to transmembrane domains for anchoring proteins to the cell surface in eukaryotes. GPI anchors are synthesized in the endoplasmic reticulum via the sequential addition of monosaccharides, fatty acids, and phosphoethanolamines to phosphatidylinositol. Deficiencies in GPI biosynthesis lead to embryonic lethality in animals and to conditional lethality in eukaryotic microbes by blocking cell growth, cell division, or morphogenesis. We report the genetic and phenotypic analysis of insertional mutations disrupting SETH1 and SETH2, which encode Arabidopsis homologs of two conserved proteins involved in the first step of the GPI biosynthetic pathway. seth1 and seth2 mutations specifically block male transmission and pollen function. This results from reduced pollen germination and tube growth, which are associated with abnormal callose deposition. This finding suggests an essential role for GPI anchor biosynthesis in pollen tube wall deposition or metabolism. Using transcriptomic and proteomic approaches, we identified 47 genes that encode potential GPI-anchored proteins that are expressed in pollen and demonstrated that at least 11 of these proteins are associated with pollen membranes by GPI anchoring. Many of the identified candidate proteins are homologous with proteins involved in cell wall synthesis and remodeling or intercellular signaling and adhesion, and they likely play important roles in the establishment and maintenance of polarized pollen tube growth.
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Genetics, Plant Biology, Biology, Fertility, Membrane Proteins, and 15 moreCell Biology, Medicine, Cell Division, Mutation, Pollen, Endoplasmic Reticulum, Flowers, Arabidopsis, Fatty Acid, Plant cell, Amino Acid Sequence, Cell Wall, Biochemistry and cell biology, Cell Growth, and Molecular Sequence Data
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The development of pollen as a vector for direct gene transfer would be a significant advance in our ability to introduce genes into plants. Such methodology should be of general utility for many plant species, and in particular for the... more
The development of pollen as a vector for direct gene transfer would be a significant advance in our ability to introduce genes into plants. Such methodology should be of general utility for many plant species, and in particular for the major monocotyledonous crop plants such as maize, wheat and barley that are recalcitrant to protoplast regeneration and that are not amenable to Agrobacterium based transformation techniques. A further advantage would be the avoidance of tissue culture steps that are time consuming and known to result in undesirable somaclonal variation. The potential of pollen as a vector for direct gene transfer has long been realized. For more than 10 years numerous investigators have attempted pollen-mediated transformation, several of which have claimed success [5, 8, 19, 23]. However the ultimate proof that transformation has taken place, that is, the demonstration of integration of foreign DNA into the nuclear genome at the molecular level and the genetic transmission of this DNA, is still lacking. This chapter presents a summary of research that has been directed towards pollen-mediated gene transfer, a detailed protocol for the delivery of DNA into pollen using particle bombardment and a discussion of factors that may be important for the successful application of this technique to obtain stably transformed plants.
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Biology, Pollen, Genome, Gene, Protoplast, and 3 moreAgrobacterium, Gene Transfer, and Springer Ebooks
In prokaryotic and eukaryotic organisms asymmetry in the fate of daughter cells is commonly established by the unequal division of intrinsically polar mother cells. First microspore division represents a striking example of such an... more
In prokaryotic and eukaryotic organisms asymmetry in the fate of daughter cells is commonly established by the unequal division of intrinsically polar mother cells. First microspore division represents a striking example of such an intrisically asymmetric division which has dramatic and determinative consequences for the differentiation or fate of the two unequal daughter cells. The aims of this chapter are to discuss the significance of asymmetric cell division for correct pollen differentiation, how asymmetric division leads to differential cell fate, how microspores develop the necessary polarity required for asymmetric division, and to summarize the results of new approaches that are being adopted to identify key genes involved in these processes.
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Biology, Cell Biology, Medicine, Biological Sciences, Plant Physiology, and 14 morePollen, Animals, Plant, Yeast, Arabidopsis, Vesicle, Amino Acid Sequence, Base Sequence, Golgi Apparatus, Recombinant Proteins, Pollen tube, Molecular Sequence Data, reverse transcriptase polymerase chain reaction, and conserved sequence
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Arabidopsis Fused kinase TWO-IN-ONE (TIO) controls phragmoplast expansion through its interaction with the Kinesin-12 subfamily proteins that anchor the plus ends of interdigitating microtubules in the phragmoplast midzone. Previous... more
Arabidopsis Fused kinase TWO-IN-ONE (TIO) controls phragmoplast expansion through its interaction with the Kinesin-12 subfamily proteins that anchor the plus ends of interdigitating microtubules in the phragmoplast midzone. Previous analyses of loss-of-function mutants and RNA interference lines revealed that TIO positively controls both somatic and gametophytic cell cytokinesis; however, knowledge of the full spectrum of TIO functions during plant development remains incomplete. To characterize TIO functions further, we expressed TIO and a range of TIO variants under control of the TIO promoter in wild-type Arabidopsis plants. We discovered that TIO-overexpressing transgenic lines produce enlarged pollen grains, arising from incomplete cytokinesis during male meiosis, and show sporophytic abnormalities indicative of polyploidy. These phenotypes arose independently in TIO variants in which either gametophytic function or the ability of TIO to interact with Kinesin-12 subfamily proteins was abolished. Interaction assays in yeast showed TIO to bind to the AtNACK2/TETRASPORE, and plants doubly homozygous for kinesin-12a and kinesin-12b knockout mutations to produce enlarged pollen grains. Our results show TIO to dominantly inhibit male meiotic cytokinesis in a dosage-dependent manner that may involve direct binding to a component of the canonical NACK-PQR cytokinesis signaling pathway.
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Asymmetric cell division at pollen mitosis I (PMI) is required to specify the differential fate of the daughter vegetative and generative cells. Cytokinesis at PMI displays specialized features, and it has been suggested that there might... more
Asymmetric cell division at pollen mitosis I (PMI) is required to specify the differential fate of the daughter vegetative and generative cells. Cytokinesis at PMI displays specialized features, and it has been suggested that there might be distinct molecular pathways underpinning different modes of cytokinesis in plants. Activation of the NACK-PQR MAP kinase signaling pathway, which is essential for somatic cell cytokinesis in tobacco, depends upon the NACK1 and NACK2 kinesin-related proteins. Their Arabidopsis orthologs, HINKEL (HIK) and TETRASPORE (TES), were reported to be essential for cytokinesis in somatic cells and in microsporocytes, respectively. More recently, HIK and TES were shown to have a functionally redundant role in female gametophytic cytokinesis. We report here that HIK and TES are co-expressed in microspores and developing pollen, and, through analysis of microspore and pollen development in double heterozygote mutants, the occurrence of cell plate expansion defects during cytokinesis at PMI. The data demonstrate a functionally redundant role for HIK and TES in cell plate expansion during male gametophytic cytokinesis, extending the concept that different modes of cytokinesis are executed by a common signaling pathway, but reinforcing the individuality of gametophytic cytokinesis in its requirement for either TES or HIK.
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Biology, Medicine, Gene expression, Biological Sciences, Phylogeny, and 15 morePlant Physiology, Pollen, Animals, Plant, Oryza Sativa, Potassium, Gene, Arabidopsis, Homeostasis, Amino Acid Sequence, Base Sequence, Gene Family, Gene expression profiling, Molecular Sequence Data, and reverse transcriptase polymerase chain reaction
Late embryogenesis abundant (lea) proteins are a diverse group of proteins present in many mono- and dicotyledonous plants. The genes encoding lea proteins are expressed in the embryo during the late stages of seed development. However,... more
Late embryogenesis abundant (lea) proteins are a diverse group of proteins present in many mono- and dicotyledonous plants. The genes encoding lea proteins are expressed in the embryo during the late stages of seed development. However, expression can also be induced in immature seeds and vegetative tissues by abscisic acid (ABA). Lea genes thus provide a model with which to study tissue-specific, developmental and hormonal regulation of expression. We used the β-glucuronidase (iudA) reporter gene (gus) to identify functional domains in the promoter of a lea gene of Arabidopsis thaliana (AtEm1). We found that a promoter fragment extending from −182 bp to +72 bp is sufficient to direct gus expression to embryos and pollen of transgenic tobacco. Gus expression in embryos and pollen was developmentally regulated, being expressed during the late stages of seed and anther development. Comparison of different deletion constructs showed that in both tissues promoter sequences between −1443 bp and −430 bp had no effect on the level of gus expression, whilst the region between −430 bp and −182 bp is necessary for full level expression. The response to ABA was studied in seedlings of transgenic tobacco transformed with a gus gene fusion construct containing −1443 bp to +72 bp of promoter. Treatment with 50 μM ABA resulted in a 3–4-fold increase in GUS activity, indicating that ABA induction of AtEm1 acts at least in part at the level of transcription. Conserved regulatory elements were identified in the promoter of AtEm1 by sequence analysis. The possible role of these elements, and the significance of the observed gus expression in pollen are discussed.
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The pollen grains of seed plants are both remarkable and intensively studied structures that have evolved to ensure delivery of the male gametes to the embryo sac during sexual reproduction. Keywords: pollen; male gametophyte;... more
The pollen grains of seed plants are both remarkable and intensively studied structures that have evolved to ensure delivery of the male gametes to the embryo sac during sexual reproduction. Keywords: pollen; male gametophyte; microgametophyte; cell differentiation; vegetative cell; generative cell; sperm cells; asymmetric division
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In order to optimize transient gene expression in Norway spruce pollen after DNA delivery with particle bombardment, effects of different conditions during homhardmenl were analysed using β‐glucuroniduse (GUS) driven by the rice Act I... more
In order to optimize transient gene expression in Norway spruce pollen after DNA delivery with particle bombardment, effects of different conditions during homhardmenl were analysed using β‐glucuroniduse (GUS) driven by the rice Act I promoter and Inciferase (LUS) driven by the tomato !at52 promoter as reporter genes. Transient gene expression was significantly increased hy using two bombardments. Also the distance from the stopping plate to the sample was critical to gam maximum gene expression. There was no significant difference between gold and tungsten particles, and the number of positively stained pollen increased with increasing DNA concentration, from 5 to 40 pg DNA added in the DNA/tungsten solution The DNA delivery to Norway spruce pollen was most efficient at a chamber pressure above 70 kPa.
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Pollen grains are the microgametophytes of seed plants that produce the male gametes required for sexual reproduction. Through the course of evolution the haploid gametophyte generation that develops from single haploid spores has... more
Pollen grains are the microgametophytes of seed plants that produce the male gametes required for sexual reproduction. Through the course of evolution the haploid gametophyte generation that develops from single haploid spores has progressively reduced in ...
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Botany, Genetics, Plant Biology, Biology, Tobacco, and 15 moreCell Biology, Medicine, Cell Division, Microspore Culture, Pollen, Research papers, Experimental Botany, Microtubule Dynamics, Microtubules, Nicotiana Tabacum, Cytokinesis, Species Specificity, Fusion Protein, PLANT PROTEINS, and Sexual reproduction
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Genetics, MicroRNA, Plant Biology, Biology, Medicine, and 15 moreGene expression, In Situ Hybridization, Non Coding Rna, Molecular, Germ Cells, Gametophyte, Gene, Chromatin, Chromatin structure, microRNAs, Angiosperms, Plant Development, Gametogenesis, Gene expression profiling, and Gene expression pattern
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A recent paper(1) describing the stage‐specific loss of ubiquitin (UBQ) and ubiquitinated proteins (UBQ‐Ps) during pollen development has raised some interesting questions regarding our understanding of the regulation of protein turnover... more
A recent paper(1) describing the stage‐specific loss of ubiquitin (UBQ) and ubiquitinated proteins (UBQ‐Ps) during pollen development has raised some interesting questions regarding our understanding of the regulation of protein turnover during cellular differentiation and the specialized development of the pollen grain. The authors, Callis and Bedinger(1), describe experiments in which the profiles of free and protein‐conjugated ubiquitin were examined during pollen development. UBQ and UBQ‐Ps were immunologically detected in extracts of microspores and maturing pollen of maize at six developmental stages. Their results remarkably demonstrate that UBQ and UBQ‐Ps decline to barely detectable levels during the final stages of pollen development.
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Copyright information: Taken from "MADS-complexes regulate transcriptome dynamics during pollen maturation"http://genomebiology.com/content/8/11/R249Genome Biology 2007;8(11):R249-R249.Published online 22 Nov... more
Copyright information: Taken from "MADS-complexes regulate transcriptome dynamics during pollen maturation"http://genomebiology.com/content/8/11/R249Genome Biology 2007;8(11):R249-R249.Published online 22 Nov 2007PMCID:PMC2258202. Overview of the presence (green), absence (red), and reduced abundance (orange) of the five MIKC* complexes in different mutant backgrounds. Values represent the number (upper row) and percentage (lower row) of AtMIKC*-controlled genes that were downregulated and upregulated in each of the mutants. Graphical representation of the numbers of significantly affected genes shared by different mutants (based on the FIRe macro [38]); virtually all genes affected in and pollen are also affected in /pollen.
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SummaryThe formation of gametes is a key step in the life cycle of any sexually reproducing organism. In flowering plants, gametes develop in haploid structures termed gametophytes that comprise a few cells. The female gametophyte forms... more
SummaryThe formation of gametes is a key step in the life cycle of any sexually reproducing organism. In flowering plants, gametes develop in haploid structures termed gametophytes that comprise a few cells. The female gametophyte forms gametic cells and flanking accessory cells. During a screen for regulators of egg‐cell fate, we isolated three mutants, lachesis (lis), clotho (clo) and atropos (ato), that show deregulated expression of an egg‐cell marker. We have previously shown that, in lis mutants, which are defective for the splicing factor PRP4, accessory cells can differentiate gametic cell fate. Here, we show that CLOTHO/GAMETOPHYTIC FACTOR 1 (CLO/GFA1) is necessary for the restricted expression of egg‐ and central‐cell fate and hence reproductive success. Surprisingly, infertile gametophytes can be expelled from the maternal ovule tissue, thereby preventing the needless allocation of maternal resources to sterile tissue. CLO/GFA1 encodes the Arabidopsis homologue of Snu114, a protein that is considered to be an essential component of the spliceosome. In agreement with their proposed role in pre‐mRNA splicing, CLO/GFA1 and LIS co‐localize to nuclear speckles. Our data also suggest that CLO/GFA1 is necessary for the tissue‐specific expression of LIS. Furthermore, we demonstrate that ATO encodes the Arabidopsis homologue of SF3a60, a protein that has been implicated in pre‐spliceosome formation. Our results thus establish that the restriction of gametic cell fate is specifically coupled to the function of various core spliceosomal components.
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The response of oilseed rape cultivars to infection with Agrobacterium tumefaciens and A. rhizogenes and the possibility of regenerating genetically transformed oilseed rape plants were examined. The frequency at which Agrobacterium... more
The response of oilseed rape cultivars to infection with Agrobacterium tumefaciens and A. rhizogenes and the possibility of regenerating genetically transformed oilseed rape plants were examined. The frequency at which Agrobacterium induced galls or hairy-roots on in vitro cultured plants ranged from 10% to 70%, depending on the cultivar. From galls induced by the tumorigenic strain T37, known to be strongly shoot inducing on tobacco, roots developed frequently. Occasionally, shoots formed and some of these produced tumour cell specific nopaline. Attempts to grow the transformed shoots into plants have so far been unsuccessful. Whole plants transformed with Ri-T-DNA, however, were regenerated. These had crinkled leaves and abundant, frequently branching roots that showed reduced geotropism, similar to previously isolated Ri T-DNA transformed tobacco and potato plants. The transformed oilseed rape plants flowered, but failed to form seeds.
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Botany, Genetics, Biology, Medicine, Potato, and 15 moreBiological Sciences, Plant Transformation, Genetic transformation, Cultivar, Gravitropism, Root development, Brassica, Brassica Napus, In vitro culture, Plant Development, Rhizobiaceae, Agrobacterium, Hairy roots, Agrobacterium tumefaciens, and Oilseed rape
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Genetics, Molecular Evolution, Biology, Medicine, Arabidopsis thaliana, and 15 moreBiological Sciences, Animals, Gene, Arabidopsis, Gene Structure, Nicotiana Tabacum, Brassica, Brassica Napus, Amino Acid Profile, Intron, Amino Acid Sequence, Gene Family, Exon, Molecular Sequence Data, and Glycogen Synthase Kinase
Cellular patterning and differentiation in plants depend on the balance of asymmetric and symmetric divisions. Patterning of the male gametophyte (pollen grains) in flowering plants requires asymmetric division of the microspore followed... more
Cellular patterning and differentiation in plants depend on the balance of asymmetric and symmetric divisions. Patterning of the male gametophyte (pollen grains) in flowering plants requires asymmetric division of the microspore followed by a symmetric division of the germ cell to produce three highly differentiated cells: a single vegetative cell and two sperm cells. In Arabidopsis sidecar pollen (scp) mutants a proportion of microspores first divide symmetrically, and then go on to produce &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;four-celled&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; pollen with an extra vegetative cell; however, details of the timing and origin of phenotypic defects in scp and the identity of the SCP gene have remained obscure. Comparative analysis of the original hypomorphic scp-1 allele and a T-DNA-induced null allele, scp-2, revealed that in the absence of SCP, microspores undergo normal nuclear positioning, but show delayed entry into mitosis, increased cell expansion and alterations in the orientation of nuclear division. We identified the SCP gene to encode a male gametophyte-specific LATERAL ORGAN BOUNDARIES DOMAIN/ASYMMETRIC LEAVES 2-like (LBD/ASL) protein that is expressed in microspore nuclei in a tightly regulated phase-specific manner. Therefore, our study demonstrates that the correct patterning of male gametophyte depends on the activity of a nuclear LBD/ASL family protein that is essential for the correct timing and orientation of asymmetric microspore division.
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... Micro-electrophoretic analysis of heter-odimeric isozymes such as phosphoglucoisomerase in total pollen extracts and sporophytic tissues of Clarkia extended the biochemical evidence for haploid gene expression (Weeden &amp;amp;... more
... Micro-electrophoretic analysis of heter-odimeric isozymes such as phosphoglucoisomerase in total pollen extracts and sporophytic tissues of Clarkia extended the biochemical evidence for haploid gene expression (Weeden &amp;amp; Gottlieb, 1979). Mulcahy et al. ...