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Michael Freeling - One of the best experts on this subject based on the ideXlab platform.
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the maize gene Liguleless2 encodes a basic leucine zipper protein involved in the establishment of the leaf blade sheath boundary
Genes & Development, 1998Co-Authors: Justine Walsh, Cynthia A Waters, Michael FreelingAbstract:The blade and sheath of a maize leaf are separated by a linear epidermal fringe, the Ligule, and two wedge-like structures, the auricles. In plants homozygous for the null mutation, Liguleless2-reference (lg2-R), the Ligule and auricles are often absent or positioned incorrectly and the blade-sheath boundary is diffuse. This phenotype is in contrast to that of Liguleless1-reference (lgl-R) mutant plants, which have a more defined boundary even in the absence of the Ligule and auricles. Additionally, mosaic analysis indicates the lg2-R phenotype is cell-nonautonomous and the lg1-R phenotype is cell-autonomous. Using scanning electron microscopy we show that lg2-R mutant plants are affected before the first visible sign of Ligule and auricle formation. We have cloned the Lg2+ gene through a Mutator-8 transposon insertion allele, and verified it with five independently derived alleles. The comparison of genomic DNA and cDNA sequences reveals an open reading frame encoding a protein of 531 amino acids with partial homology to a subclass of plant basic leucine zipper (bZIP) transcription factors. Although a large body of molecular and biochemical characterization exists on this subclass of bZIP proteins, our work represents the first report of a mutant phenotype within this group. A specific reverse transcriptase (RT)-PCR assay shows LG2 mRNA expression in meristem/developing Ligule regions. RT-PCR also shows that LG2 mRNA accumulation precedes that of LG1 mRNA. The mutant phenotype and expression analysis of lg2 suggest an early role in initiating an exact blade-sheath boundary within the young leaf primordia.
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The maize gene Liguleless2 encodes a basic leucine zipper protein involved in the establishment of the leaf blade–sheath boundary
Genes & development, 1998Co-Authors: Justine Walsh, Cynthia A Waters, Michael FreelingAbstract:The blade and sheath of a maize leaf are separated by a linear epidermal fringe, the Ligule, and two wedge-like structures, the auricles. In plants homozygous for the null mutation, Liguleless2-reference (lg2-R), the Ligule and auricles are often absent or positioned incorrectly and the blade-sheath boundary is diffuse. This phenotype is in contrast to that of Liguleless1-reference (lgl-R) mutant plants, which have a more defined boundary even in the absence of the Ligule and auricles. Additionally, mosaic analysis indicates the lg2-R phenotype is cell-nonautonomous and the lg1-R phenotype is cell-autonomous. Using scanning electron microscopy we show that lg2-R mutant plants are affected before the first visible sign of Ligule and auricle formation. We have cloned the Lg2+ gene through a Mutator-8 transposon insertion allele, and verified it with five independently derived alleles. The comparison of genomic DNA and cDNA sequences reveals an open reading frame encoding a protein of 531 amino acids with partial homology to a subclass of plant basic leucine zipper (bZIP) transcription factors. Although a large body of molecular and biochemical characterization exists on this subclass of bZIP proteins, our work represents the first report of a mutant phenotype within this group. A specific reverse transcriptase (RT)-PCR assay shows LG2 mRNA expression in meristem/developing Ligule regions. RT-PCR also shows that LG2 mRNA accumulation precedes that of LG1 mRNA. The mutant phenotype and expression analysis of lg2 suggest an early role in initiating an exact blade-sheath boundary within the young leaf primordia.
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Sectors expressing the homeobox gene Liguleless3 implicate a time-dependent mechanism for cell fate acquisition along the proximal-distal axis of the maize leaf
Development (Cambridge England), 1997Co-Authors: Gary J. Muehlbauer, John E. Fowler, Michael FreelingAbstract:The longitudinal axis of the maize leaf is composed of, in proximal to distal order, sheath, Ligule, auricle and blade. The semidominant Liguleless3-O (Lg3-O) mutation disrupts leaf development at the ligular region of the leaf midrib by transforming blade to sheath. In a previous study, we showed that leaf sectors of Lg3 mutant activity are cell nonautonomous in the transverse dimension and can confer several alternative developmental fates (Fowler, Muehlbauer and Freeling (1996) Genetics 143, 489–503). In our present study we identify five Lg3 sector types in the leaf: sheath-like with displaced Ligule (sheath-like), sheath-like with ectopic Ligule (ectopic Ligule), auricle-like, macro-hairless blade and wild-type blade. The acquisition of a specific sector fate depends on the timing of Lg3 expression. Early Lg3 expression results in adoption of the sheath-like phenotype at the Ligule position (a proximal cell fate), whereas later Lg3 expression at the same position results in one of the more distal cell fates. Furthermore, sheath-like Lg3 sectors exhibit a graded continuum of phenotypes in the transformed blade region from the most proximal (sheath) to the most distal (wild-type blade), suggesting that cell fate acquisition is a gradual process. We propose a model for leaf cell fate acquisition based on a timing mechanism whereby cells of the leaf primordium progress through a maturation schedule of competency stages which eventually specify the cell types along the proximal to distal axis of the leaf. In addition, the lateral borders between Lg3 ‘on’ sectors and wild-type leaf sometimes provide evidence of no spreading of the transformed phenotype. In these cases, competency stages are inherited somatically.
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Interactions of Liguleless1 and Liguleless2 Function During Ligule Induction in Maize
Genetics, 1996Co-Authors: Lisa Harper, Michael FreelingAbstract:The maize Ligule is an adaxial membranous structure on the leaf that develops at the boundary of the sheath and blade. The Ligule and the associated auricle are dispensable structures, amenable to genetic manipulation. We present here a genetic analysis of Liguleless1 (lg1) and Liguleless2 (lg2), the two genes known to be uniquely necessary for Ligule and auricle development. We show that both reference mutant alleles, lg1-R and lg2-R, are null alleles. The double mutant phenotype suggests that lg1 and lg2 act in the same pathway. Indeed, the dosage of a functional allele at either gene affects the null phenotype of the other. While lg1 function has previously been shown to be cell-autonomous, here we show that the lg2-R phenotype is cell-nonautonomous, suggesting lg1 and lg2 play different roles in the Ligule-auricle induction mechanism. We present a model in which early lg2 function specifies the precise position where Ligule and auricle will develop. Later lg2 function interacts with lg1 function (either directly or indirectly) to transmit and receive a make-Ligule-make-auricle inductive signal.
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Mosaic Analysis of the Liguleless3 Mutant Phenotype in Maize by Coordinate Suppression of Mutator-insertion Alleles
Genetics, 1996Co-Authors: John E. Fowler, Gary J. Muehlbauer, Michael FreelingAbstract:Ligubless3-O ( Lg3-O ) transforms the leaf blade, auricle and Ligule into sheath around the midrib region. We conducted a genetic mosaic analysis of the Lg3 phenotype to determine the site of Lg3 gene action. Combining the Mutator ( Mu ) suppressible Lg3-Or211 and al-mum2 alleles in a Mu -active background generated a stock wherein somatic loss of Mu activity resulted in anthocyanin-marked clonal sectors expressing Lg3 in the leaf. Lg3-Or211 plants appear wild type in a Mu -active line, but Mu -inactive plants express a severe Lg3 phenotype. We observed four sector classes: wild type, sheath-like with Ligule displacement, sheath-like with ectopic Ligule, and auricle-like. The mutation does not cause transformation to a specific cell or regional identity. Lg3-Or211 activity in the mesophyll alters wild-type epidermal cell fates; activity in epidermis seems funtionless. Lg3 mutant activity has a nonautonomous, cell-layer-specific function in the transverse dimension. In the lateral dimension, sectors of Lg3 mutant phenotype can exhibit either cell-autonomous or nonautonomous effects. Our work demonstrates that mosaic analysis by coordinate suppression of Mu -induced alleles is useful for analyzing the cell autonomy of genetically defined functions.
Curtis J. Nelson - One of the best experts on this subject based on the ideXlab platform.
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secondary cell wall deposition causes radial growth of fibre cells in the maturation zone of elongating tall fescue leaf blades
Annals of Botany, 2002Co-Authors: Jennifer W Macadam, Curtis J. NelsonAbstract:A gradient of development consisting of successive zones of cell division, cell elongation and cell maturation occurs along the longitudinal axis of elongating leaf blades of tall fescue (Festuca arundinacea Schreb.), a C3 grass. An increase in specific leaf weight (SLW; dry weight per unit leaf area) in the maturation region has been hypothesized to result from deposition of secondary cell walls in structural tissues. Our objective was to measure the transverse cell wall area (CWA) associated with the increase in SLW, which occurs following the cessation of leaf blade elongation at about 25 mm distal to the Ligule. Digital image analysis of transverse sections at 5, 15, 45, 75 and 105 mm distal to the Ligule was used to determine cell number, cell area and protoplast area of structural tissues, namely fibre bundles, mestome sheaths and xylem vessel elements, along the developmental gradient. Cell diameter, protoplast diameter and area, and cell wall thickness and area of fibre bundle cells were calculated from these data. CWA of structural tissues increased in sections up to 75 mm distal to the Ligule, confirming the role of cell wall deposition in the increase in SLW (r2 = 0·924; P < 0·01). However, protoplast diameter of fibre cells did not decrease significantly as CWA increased, although mean thickness of fibre cell walls increased by 95 % between 15 and 105 mm distal to the Ligule. Therefore, secondary cell wall deposition in fibre bundles of tall fescue leaf blades resulted in continued radial expansion of fibre cells rather than in a decrease in protoplast diameter. a 2002 Annals of Botany Company
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Response of Fructan to Water Deficit in Growing Leaves of Tall Fescue
Plant physiology, 1994Co-Authors: William C. Spollen, Curtis J. NelsonAbstract:Changes in dry matter and water-soluble carbohydrate components, especially fructan, were examined in the basal 25 mm of expanding leaf blades of tall fescue (Festuca arundinacea Schreb.) to assess their roles in plant response to water deficit. Water was withheld from vegetative plants grown in soil in controlled-environment chambers. As stress progressed, leaf elongation rate decreased sooner in the light period than it did in the dark period. The decrease in growth rate in the dark period was associated with a decrease in local relative elongation rates and a shortening of the elongation zone from about 25 mm (control) to 15 mm. Dry matter content of the leaf base increased 23% during stress, due mainly to increased water-soluble carbohydrate near the Ligule and to increased water-soluble, carbohydrate-free dry matter at distal positions. Sucrose content increased 258% in the leaf base, but especially (over 4-fold) within 10 mm of the Ligule. Hexose content increased 187% in the leaf base. Content of total fructan decreased to 69% of control, mostly in regions farther from the Ligule. Fructan hydrolysis could account for the hexose accumulated. Stress caused the osmotic potential to decrease throughout the leaf base, but more toward the Ligule. With stress there was 70% less direct contribution of low-degree-of-polymerization fructan to osmotic potential in the leaf base, but that for sucrose and hexose increased 96 and 67%, respectively. Thus, fructan metabolism is involved but fructan itself contributes only indirectly to osmotic adjustment.
Sarah Hake - One of the best experts on this subject based on the ideXlab platform.
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Transcriptomic Analyses Indicate That Maize Ligule Development Recapitulates Gene Expression Patterns That Occur during Lateral Organ Initiation
The Plant cell, 2014Co-Authors: Robyn Johnston, Anne W. Sylvester, Minghui Wang, Qi Sun, Sarah Hake, Michael J. ScanlonAbstract:Development of multicellular organisms proceeds via the correct interpretation of positional information to establish boundaries that separate developmental fields with distinct identities. The maize (Zea mays) leaf is an ideal system to study plant morphogenesis as it is subdivided into a proximal sheath and a distal blade, each with distinct developmental patterning. Specialized Ligule and auricle structures form at the blade-sheath boundary. The auricles act as a hinge, allowing the leaf blade to project at an angle from the stem, while the Ligule comprises an epidermally derived fringe. Recessive Liguleless1 mutants lack Ligules and auricles and have upright leaves. We used laser microdissection and RNA sequencing to identify genes that are differentially expressed in discrete cell/tissue-specific domains along the proximal-distal axis of wild-type leaf primordia undergoing Ligule initiation and compared transcript accumulation in wild-type and Liguleless1-R mutant leaf primordia. We identified transcripts that are specifically upregulated at the blade-sheath boundary. A surprising number of these “Ligule genes” have also been shown to function during leaf initiation or lateral branching and intersect multiple hormonal signaling pathways. We propose that genetic modules utilized in leaf and/or branch initiation are redeployed to regulate Ligule outgrowth from leaf primordia.
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Gene regulatory interactions at lateral organ boundaries in maize
Development (Cambridge England), 2014Co-Authors: Michael W. Lewis, Nathalie Bolduc, Kayley Hake, Yadanar Htike, Angela Hay, Héctor Candela, Sarah HakeAbstract:Maize leaves have distinct tissues that serve specific purposes. The blade tilts back to photosynthesize and the sheath wraps around the stem to provide structural support and protect young leaves. At the junction between blade and sheath are the Ligule and auricles, both of which are absent in the recessive Liguleless1 (lg1) mutant. Using an antibody against LG1, we reveal LG1 accumulation at the site of Ligule formation and in the axil of developing tassel branches. The dominant mutant Wavy auricle in blade1 (Wab1-R) produces ectopic auricle tissue in the blade and increases the domain of LG1 accumulation. We determined that wab1 encodes a TCP transcription factor by positional cloning and revertant analysis. Tassel branches are few and upright in the wab1 revertant tassel and have an increased branch angle in the dominant mutant. wab1 mRNA is expressed at the base of branches in the inflorescence and is necessary for LG1 expression. wab1 is not expressed in leaves, except in the dominant mutant. The domain of wab1 expression in the Wab1-R leaf closely mirrors the accumulation of LG1. Although wab1 is not needed to induce lg1 expression in the leaf, LG1 is needed to counteract the severe phenotype of the dominant Wab1-R mutant. The regulatory interaction of LG1 and WAB1 reveals a link between leaf shape and tassel architecture, and suggests the Ligule is a boundary similar to that at the base of lateral organs.
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Natural Variation at sympathy for the Ligule Controls Penetrance of the Semidominant Liguleless narrow-R Mutation in Zea mays
G3 (Bethesda Md.), 2014Co-Authors: Elizabeth Buescher, Sarah Hake, Jihyun Moon, Anne M. Runkel, Brian P. DilkesAbstract:Leaf architecture determines plant structural integrity, light harvesting, and economic considerations such as plant density. Ligules, junctions at the leaf sheath and blade in grasses, protect stalks from environmental stresses and, in conjunction with auricles, controls leaf angle. Previous studies in mutants have recessive Liguleless mutants (lg1 and lg2) and dominant mutations in knotted1-like homeobox genes (Lg3-O, Lg4, and Kn1) involved in Ligule development. Recently, a new semidominant Liguleless mutant, Liguleless narrow (Lgn-R), has been characterized in maize that affects Ligule and auricle development and results in a narrow leaf phenotype. We show that quantitative genetic variation affects penetrance of Lgn-R. To examine the genetic architecture underlying Lgn-R expressivity, crosses between Lgn-R/+ mutants in a B73 background and intermated B73 x Mo17 recombinant inbred lines were evaluated in multiple years and locations. A single main-effect quantitative trait locus (QTL) on chromosome 1 (sympathy for the Ligule; sol) was discovered with a Mo17-contributed allele that suppressed Lgn-R mutant phenotypes. This QTL has a genetic-interaction with a locus on chromosome 7 (lucifer; lcf) for which the B73-contributed allele increases the ability of the solMo17 allele to suppress Lgn-R. Neither of the genetic intervals likely to contain sol or lcf overlap with any current Liguleless genes nor with previously identified genome-wide association QTL connected to leaf architecture. Analysis of phenotypes across environments further identified a genotype by enviroment interaction determining the strength of the sol x lcf interaction.
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Mosaic analysis of the dominant mutant, Gnarley1-R, reveals distinct lateral and transverse signaling pathways during maize leaf development
Development (Cambridge England), 1999Co-Authors: Toshi Foster, Bruce Veit, Sarah HakeAbstract:Maize leaves are organized into two major domains along the proximal-distal axis: a broad flat blade at the distal end of the leaf, and a narrow, thickened sheath that encircles the stem. Between the blade and sheath are two wedge-shaped tissues called auricles, and the Ligule, an epidermally derived fringe. Members of the Knotted1 (Kn1) family of mutations change the shape and position of both Ligule and auricle, thus disturbing the overall pattern of the leaf. Here we present the results of a mosaic analysis of Gnarley1-R (Gn1-R), which like members of the Kn1 family, affects the Ligule and auricle. Gn1-R is distinct, however, in altering the dimensions of cells that make up sheath tissue. To gain insight into the Gn1-R phenotype, we performed a mosaic analysis using X-ray induced chromosome breakage to generate wild-type (gn1+/−) sectors in otherwise Gn1-R leaves. These sectors allowed us to determine whether Gn1-R acts non-autonomously to influence adjacent cells. Most aspects of the Gn1-R phenotype, such as Ligule position, inhibition of auricle development, and sheath thickness showed autonomy in the lateral dimension (leaf width). In contrast, all aspects of the Gn1-R phenotype were non-autonomous in the transverse dimension (leaf thickness), suggesting that signaling occurs between cell layers in the leaf. These results support a model for distinct signaling pathways along lateral versus transverse axes of a developing leaf.
Nigel Chaffey - One of the best experts on this subject based on the ideXlab platform.
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Physiological anatomy and function of the membranous grass Ligule.
New Phytologist, 2000Co-Authors: Nigel ChaffeyAbstract:Of the three component organs of the grass leaf – blade, sheath and Ligule – the Ligule is the least studied and the least understood. Traditionally, it has been assumed to act in a passive way in protecting the culm and leaves that it encloses from the entry of water, dust and harmful spores. However, ultrastructural and cytochemical studies of the membranous Ligules of several taxa, particularly Lolium species, have challenged that rather simplistic view and suggest that these Ligules play a more active role in the life of the grass plant as a secretory tissue. This review summarizes the evidence for the latter notion, assesses the validity of both the passive and active hypotheses of membranous Ligule function and notes similarities between membranous grass Ligules, root caps and lycopsid Ligules.
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Structure and Function of the Root Cap of Lolium temulentum L. (Poaceae): Parallels with the Ligule
Annals of Botany, 1996Co-Authors: Nigel ChaffeyAbstract:Structure of the root cap of Lolium temulentum L. and of the chemistry of its secretory product were investigated with conventional transmission electron microscopy, zinc iodide‐osmium tetroxide impregnation, and use of protein and polysaccharide localization techniques at the ultrastructural level. Structural and functional information concerning the root cap is compared with that previously obtained for the membranous Ligule of this species. Similarities between root cap cells and adaxial epidermal cells of the Ligule are described and discussed. It is concluded that both systems are secretory and represent a similar response to the common problem of easing the passage of growing organs against the soil or other plant parts. # 1996 Annals of Botany Company
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Structure and function of the membranous grass Ligule: a comparative study
Botanical Journal of the Linnean Society, 1994Co-Authors: Nigel ChaffeyAbstract:Membranous Ligules of 49 grass species, representing ten tribes, were anatomically studied using light, fluorescence and transmission electron microscopy. Great variety in Ligule abaxial surface anatomy was found but internally all Ligules so studied possess a tripartite structure of two uniseriate epidermes enclosing a mesophyll tissue of varying thickness. Chloroplasts were present in most of the Ligules (where this feature was determined) supporting the view that this is a photosynthetic leaf organ. Of the 36 species examined by fluorescence microscopy eight showed evidence of having a gland-like adaxial epidermis with numerous mitochondria, dictyosomes, strands of rough endoplasmic reticulum and fibrillar material within the periplasmic space next to the outer tangential wall. Existing hypotheses of Ligule function are discussed in the light of these anatomical results, and a new hypothesis is proposed.
Gynheung An - One of the best experts on this subject based on the ideXlab platform.
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mutations in the rice Liguleless gene result in a complete loss of the auricle Ligule and laminar joint
Plant Molecular Biology, 2007Co-Authors: Jongjin Park, Gynheung AnAbstract:The area between the upper part of the leaf sheath and the basal portion of the leaf blade contains several specialized organs, such as the laminar joint, auricle and Ligule. Here we report the identification of T-DNA insertional mutant lines that lack all of these organs. The gene knocked out in the mutant lines encodes a protein that contains a SBP (SQUAMOSA promoter Binding Protein)-domain and is highly homologous to the maize LiguleLESS1 (LG1) gene. At the amino acid sequence level, the OsLG1 protein is 69% identical to maize LG1 and 78% identical to barley LG1. We named the rice gene OsLiguleLESS1 (OsLG1). Transient expression of an OsLG1:RFP (Red Fluorescent Protein) fusion protein indicated that the protein is localized to the nucleus. Transgenic plants harboring the OsLG1 promoter:GUS (β-glucuronidase) reporter gene construct display preferential expression in developing laminar joint regions and meristemic regions. The gene is also weakly expressed in the Ligule, auricles, and leaf sheaths at the basal region. These results indicate that OsLG1 is a transcriptional factor that plays an important role in building the laminar joint between leaf blade and leaf sheath boundary, thereby controlling Ligule and auricle development.