PubMed Health⌕ Search

Biomedical subjects

P W Becraft

Publications and source records attributed to P W Becraft.

14 recordsLinked to original sources
PubMed2001

Cell fate specification in the cereal endosperm.

While superficially simple, endosperm development is a complex, dynamic process. Cereal endosperms contain three major cell types: starchy endosperm, transfer cells and aleurone. The localized accumulation of the END1 transcript in the syncitial endosperm suggests that signals from the maternal placental tissue specify transfer cell type early. Aleurone fate is plastic and requires the continual input of positional cues to maintain cell identity. Starchy endosperm appears to be the default cell type. Mutant patterns suggest that a regulatory hierarchy integrates endosperm development. Requirements for gametic imprinting, maternal : paternal genome ratios and putative chromatin modeling factors indicate the importance of genomic control.

Cell Differentiation↗
PubMed2001

Plant steroids recognized at the cell surface.

Plants might use a markedly different mechanism for steroid signaling than animals. In animals, steroid hormone signals are generally mediated by receptors inside the cell. However, a recent report by He et al. indicates that, in plants, steroids appear to be perceived at the plasma membrane rather than by intracellular receptors.

Animals↗
PubMed2001

The maize CRINKLY4 receptor kinase controls a cell-autonomous differentiation response.

The maize (Zea mays) CRINKLY4 (cr4) gene encodes a receptor-like kinase that controls a variety of cell differentiation responses, particularly in the leaf epidermis and in the aleurone of the endosperm. In situ hybridization indicated that the cr4 transcript is present throughout the shoot apical meristem and young leaf primordia. A genetic mosaic analysis was conducted to test whether CR4 signal transduction directly regulated the cellular processes associated with differentiation or whether differentiation was controlled through the production of a secondary signal. Genetic mosaics were created using gamma-rays to induce chromosome breakage in a cr4/Cr4+ heterozygote. The mutant cr4 allele was marked with the albino mutation, Oy-700. Breakage and loss of the chromosome arm carrying the wild-type alleles created a sector of albino, cr4 mutant tissue in an otherwise normal leaf. Analysis of such sectors indicated that cr4 functions cell autonomously to regulate cell morphogenesis, implying that CR4 signal transduction regulates cell differentiation through strictly intracellular functions and not the production of secondary intercellular signals. However, several sectors altered cell patterning in wild-type tissue adjacent to the sectors, suggesting that cr4 mutant cells are defective in the production of other lateral signals.

Anthocyanins↗
PubMed2000

The maize CR4 receptor-like kinase mediates a growth factor-like differentiation response.

The maize crinkly4 (cr4) gene encodes a predicted receptor kinase that is required for the normal differentiation of leaf epidermis (Becraft et al., 1996). Here we confirm that the presumptive cytoplasmic domain is capable of autophosphorylation on serine and threonine residues. The cr4 transcript is most abundant in young developing tissues of the shoot but was not detected in the root. Phenotypic analysis of strong mutant alleles indicates that cr4 functions throughout shoot development to control the differentiation of internal as well as epidermal tissues. However, epidermal cells appear most sensitive to perturbations in CR4 signaling because epidermal defects are more pronounced than internal cell defects. Epidermal cells show irregularities in shape, cell wall thickness and structure, cuticle formation, and vesicle trafficking. Some plants show tumor-like proliferations of cells on the leaves. Thus CR4 regulates an array of developmental responses including cell proliferation, fate, pattern, and differentiation suggesting a function analogous to growth factor responses in animals.

Alleles↗
PubMed2000

Positional cues specify and maintain aleurone cell fate in maize endosperm development.

A genetic analysis of maize aleurone development was conducted. Cell lineage was examined by simultaneously marking cells with C1 for anthocyanin pigmentation in the aleurone and wx1 for amylose synthesis in the starchy endosperm. The aleurone and starchy endosperm share a common lineage throughout development indicating that positional cues specify aleurone fate. Mutants in dek1 block aleurone formation at an early stage and cause peripheral endosperm cells to develop as starchy endosperm. Revertant sectors of a transposon-induced dek1 allele showed that peripheral endosperm cells remain competent to differentiate as aleurone cells until late in development. Ds-induced chromosome breakage was used to generate Dek1 loss-of-function sectors. Events occurring until late development caused aleurone cells to switch fate to starchy endosperm indicating that cell fate is not fixed. Thus, positional cues are required to specify and maintain aleurone fate and Dek1 function is required to respond to these cues. An analysis of additional mutants that disrupt aleurone differentiation suggests a hierarchy of gene functions to specify aleurone cell fate and then control aleurone differentiation. These mutants disrupt aleurone differentiation in reproducible patterns suggesting a relationship to endosperm pattern formation.

Amylose↗
PubMed1999

ROUGH SHEATH2: a Myb protein that represses knox homeobox genes in maize lateral organ primordia.

The regulation of members of the knotted1-like homeobox (knox) gene family is required for the normal initiation and development of lateral organs. The maize rough sheath2 (rs2) gene, which encodes a Myb-domain protein, is expressed in lateral organ primordia and their initials. Mutations in the rs2 gene permit ectopic expression of knox genes in leaf and floral primordia, causing a variety of developmental defects. Ectopic KNOX protein accumulation in rs2 mutants occurs in a subset of the normal rs2-expressing cells. This variegated accumulation of KNOX proteins in rs2 mutants suggests that rs2 represses knox expression through epigenetic means.

Amino Acid Sequence↗
PubMed1999

Development of the leaf epidermis.

The leaf epidermis is essential to plant survival not only because of its protective role at the interface with the plant's environment but also because of crucial developmental functions. The protoderm is set aside early in embryogenesis, possibly in the zygote. Epidermal identity is determined by the interactions of a complex set of factors, including developmental phase of the plant, regional identity within the leaf, and axiality. For the most part, these characteristics appear to be specified by internal tissues. On the other hand, the epidermis has a key role in regulating organ growth and expansion; thus interactions between the epidermis and internal tissues regulate the overall leaf architecture. Overlying this is the specification of different cell types within the epidermis. Some aspects of this appear to involve interactions with internal tissues but the patterning of many epidermal cell types seems to occur within the two-dimensional field of the epidermis itself and to require both cell signaling and cell lineage dependent mechanisms. Genetic analyses have provided much of the insight into the underlying principles that regulate epidermal development and a number of molecules important for various aspects of the process have been identified. Yet, for the most part, our understanding of the molecular basis for each component of epidermal development is still rudimentary and we have not yet scratched the surface of understanding how these pieces are integrated. The emerging technologies of functional genomics will provide powerful tools for solving these problems and the near future is likely to produce rapid progress.

Cell Division↗
PubMed1996

CRINKLY4: A TNFR-like receptor kinase involved in maize epidermal differentiation.

The maize crinkly4 (cr4) mutation affects leaf epidermis differentiation such that cell size and morphology are altered, and surface functions are compromised, allowing graft-like fusions between organs. In the seed, loss of cr4 inhibits aleurone formation in a pattern that reflects the normal progression of differentiation over the developing endosperm surface. The cr4 gene was isolated by transposon tagging and found to encode a putative receptor kinase. The extracellular domain contains a cysteine-rich region similar to the ligand binding domain in mammalian tumor necrosis factor receptors (TNFRs) and seven copies of a previously unknown 39-amino acid repeat. The results suggest a role for cr4 in a differentiation signal.

Amino Acid Sequence↗
PubMed1995

Ectopic expression of the knox homeo box gene rough sheath1 alters cell fate in the maize leaf.

Rough sheath1 (Rs1) is a dominant mutation that alters cell fate and causes unregulated cell division and expansion in the maize leaf. A knox (Kn1 like-homeo box gene) sequence closely linked to the Rs1-O mutation was cloned and shown by transposon mutagenesis to encode the rs1 gene. The deduced amino acid sequence of the RS1 protein is highly similar to KN1 in the homeo domain but contains a unique amino-terminal region. rs1 is expressed in the shoot apical meristem in a circular pattern preceding leaf initiation, but is not detectable in leaf primordia or mature leaves in normal plants. Rings of rs1 expression subtend leaf insertion sites in the shoot, and lateral organ primordia in inflorescence and floral meristems. The timing and position of rs1 expression in meristems suggests a possible role for rs1 in patterning the placement of lateral organs along the axis of the shoot. In contrast to wild type, rs1 is expressed in early leaf primordia of Rs1 mutant plants, suggesting that ectopic expression causes the mutant phenotype. Ectopic expression in Rs1-O plants suggests the ligular [corrected] region is more competent to respond to rs1 than blade or sheath tissues.

Amino Acid Sequence↗
PubMed1994

Genetic analysis of Rough sheath1 developmental mutants of maize.

Maize Rough sheath1 (Rs1) mutants are dominant and cause a proliferation of sheath-like tissue at the base of the blade and throughout the ligular region. They also cause ligule displacement, a chaotic pattern of vasculature and abnormal cellular structure of vascular bundles. The affected region of Rs1-O leaves displays genetic and morphological attributes of both sheath and auricle, suggesting an overlap of these genetic programs. The rs1 locus maps approximately 26 map units distal to opaque2 (o2) on chromosome 7S, defining a new distal-most locus on the genetic map. Three mutant alleles, Rs1-O, Rs1-1025 and Rs1-Z, all display similar phenotypes. The mutations are completely dominant and the Rs1-O phenotype is not affected by dosage of the chromosome arm carrying the rs1+ allele, indicating that these alleles are neomorphic. Analysis of genetic mosaics showed that the Rs1-O phenotype is non-cell-autonomous, suggesting that intercellular signals convey the phenotype. Rs1 mutant phenotypes are affected by modifiers present in particular genetic backgrounds. An enhancer of Rs1-O was identified; segregation data imply a single recessive gene, ers1. Rs1 mutants were also found to enhance the expression of unlinked rs2 and Rs4 mutants, suggesting that these mutations affect similar developmental processes. We discuss the phenotypic and genetic similarities between Rs1 and Knotted 1 (Kn1) mutants that led to the identification of rs1 as a kn1-like homeobox gene (unpublished data).

Crosses, Genetic↗
PubMed1992

Cell interactions in plants.

Plant cells interact during development through diverse mechanisms that range from genetically encoded signals to physical stresses. Pollen self-incompatibility is the best understood cell interaction in plants. Analysis of genes that appear to be involved in specific developmental signals, such as liguleless1 from maize and GLABROUS1 from Arabidopsis, will provide clues as to the nature of cell interactions in plant development. Recent data suggest that intercellular connections may be more similar in plants and animals than previously thought.

Cell Communication↗
PubMed1991

Sectors of liguleless-1 tissue interrupt an inductive signal during maize leaf development.

The ligule and auricles separate the blade and sheath of normal maize leaves and are absent in liguleless-1 (lg1) mutant leaves. We induced chromosome breakage using X-rays to create plants genetically mosaic for lg1. In genetically mosaic leaves, when an lg1 mutant sector interrupts the normal ligule, the ligule is often displaced basipetally on the marginal side of the sector. Therefore, lg1 mutant sectors not only fail to induce ligule and auricle, but are also disrupting some form of intercellular communication that is necessary for the normally coordinated development of the ligular region. Our data are consistent with a model in which an inductive signal originates near the midvein, cannot traverse the lg1 mutant sector, and reinitiates in the wild-type tissue across the sector toward the leaf margin. The lg1 gene product, therefore, appears to be required for the transmission of this signal and could be involved with reception.

Cell Communication↗
PubMed1990

The liguleless-1 gene acts tissue specifically in maize leaf development.

The liguleless-1 (lg1) gene affects maize leaf development. In a normal maize leaf, a ligule and auricles separate the blade and sheath. The recessive lg1 mutation prevents formation of ligules and auricles during leaf development. To determine the timing and site of lg1 gene action, we compared development of wild-type and lg1 mutant leaves, and analyzed genetic mosaics composed of wild-type and lg1 mutant cells. In wild-type leaves the first sign of differentiation of the ligular region is a series of specialized anticlinal divisions in the adaxial epidermis. This establishes a distinct band of cells, from which the ligule arises via periclinal divisions. The anticlinal divisions preceding ligule formation are altered in the mutant; therefore, the gene acts early in development, before the periclinal divisions, and possibly during basipetal vascularization. Genetic mosaic analysis indicates that the lg1 gene has at least two functions with different tissue specificities: The Lg1+ wild-type allele acts autonomously in the adaxial epidermis for normal ligule development, and in internal tissues for auricle formation. Wild-type internal tissue in direct contact with lg1 epidermis appears able to induce the mutant epidermis to form a rudimentary ligule. The results indicate that the lg1 gene acts tissue specifically in an early step of ligule and auricle initiation.

In Vitro Techniques↗