Biomedical subjects

G N Drews

Publications and source records attributed to G N Drews.

8 recordsLinked to original sources

PubMed1992

Regional and cell-specific gene expression patterns during petal development.

We investigated gene expression patterns that occur during tobacco petal development. Two petal mRNA classes were identified that are present at elevated levels relative to other organs. One class is represented equally in the unpigmented tube and pigmented limb regions of the corolla. The other class accumulates preferentially within the limb region. Limb-specific mRNAs accumulate at different times during corolla development, peak in prevalence prior to flower opening, and are localized in either the epidermal cell layers or the mesophyll. The epidermal- and mesophyll-specific mRNAs change abruptly in concentration within a narrow zone of the limb/tube border. Preferential accumulation of at least one limb-specific mRNA occurs within the corolla upper region early in development prior to limb maturation and pigment accumulation. Limb-specific mRNAs also accumulate preferentially within the unpigmented corolla limb region of Nicotiana sylvestris, a diploid progenitor of tobacco. Runoff transcription studies and experiments with chimeric beta-glucuronidase genes showed that petal gene organ, cell, and region specificities are controlled primarily at the transcriptional level. We conclude that during corolla development transcriptional processes act coordinately on limb-specific genes to regulate their regional expression patterns, but act individually on these genes to define their cell specificities.

Color↗

PubMed1991

Negative regulation of the Arabidopsis homeotic gene AGAMOUS by the APETALA2 product.

We characterized the distribution of AGAMOUS (AG) RNA during early flower development in Arabidopsis. Mutations in this homeotic gene cause the transformation of stamens to petals in floral whorl 3 and of carpels to another ag flower in floral whorl 4. We found that AG RNA is present in the stamen and carpel primordia but is undetectable in sepal and petal primordia throughout early wild-type flower development, consistent with the mutant phenotype. We also analyzed the distribution of AG RNA in apetela2 (ap2) mutant flowers. AP2 is a floral homeotic gene that is necessary for the normal development of sepals and petals in floral whorls 1 and 2. In ap2 mutant flowers, AG RNA is present in the organ primordia of all floral whorls. These observations show that the expression patterns of the Arabidopsis floral homeotic genes are in part established by regulatory interactions between these genes.

DNA-Binding Proteins↗

PubMed1991

Floral patterning.

In recent years, flower development has emerged as a model system for studying pattern formation in plants. Homeotic mutants with an altered pattern of floral organs have been found in many species. Recently, several of the floral homeotic genes have been isolated; and the mechanisms underlying pattern formation during flower development are beginning to be elucidated.

Genes, Homeobox↗

PubMed1991

Expression of the Arabidopsis floral homeotic gene AGAMOUS is restricted to specific cell types late in flower development.

Mutations in the AGAMOUS (AG) gene cause transformations in two adjacent whorls of the Arabidopsis flower. Petals develop in the third floral whorl rather than the normal stamens, and the cells that would normally develop into the fourth whorl gynoecium behave as if they constituted an ag flower primordium. Early in flower development, AG RNA is evenly distributed throughout third and fourth whorl organ primordia but is not present in the organ primordia of whorls one and two. In contrast to the early expression pattern, later in flower development, AG RNA is restricted to specific cell types within the stamens and carpels as cellular differentiation occurs in those organs. Ectopic AG expression patterns in flowers mutant for the floral homeotic gene APETELA2 (AP2), which regulates early AG expression, suggest that the late AG expression is not directly dependent on AP2 activity.

Gene Expression↗

PubMed1991

A genetic and molecular model for flower development in Arabidopsis thaliana.

Cells in developing organisms do not only differentiate, they differentiate in defined patterns. A striking example is the differentiation of flowers, which in most plant families consist of four types of organs: sepals, petals, stamens and carpels, each composed of characteristic cell types. In the families of flowering plants in which these organs occur, they are patterned with the sepals in the outermost whorl or whorls of the flower, with the petals next closest to the center, the stamens even closer to the center, and the carpels central. In each species of flowering plant the disposition and number (or range of numbers) of these organs is also specified, and the floral 'formula' is repeated in each of the flowers on each individual plant of the species. We do not know how cells in developing plants determine their position, and in response to this determination differentiate to the cell types appropriate for that position. While there have been a number of speculative proposals for the mechanism of organ specification in flowers (Goethe, 1790; Goebel, 1900; Heslop-Harrison, 1964; Green, 1988), recent genetic evidence is inconsistent with all of them, at least in the forms in which they were originally presented (Bowman et al. 1989; Meyerowitz et al. 1989). We describe here a preliminary model, based on experiments with Arabidopsis thaliana. The model is by and large consistent with existing evidence, and has predicted the results of a number of genetic and molecular experiments that have been recently performed.

Models, Chemical↗

PubMed1990

The protein encoded by the Arabidopsis homeotic gene agamous resembles transcription factors.

Mutations in the homeotic gene agamous of the plant Arabidopsis cause the transformation of the floral sex organs. Cloning and sequence analysis of agamous suggest that it encodes a protein with a high degree of sequence similarity to the DNA-binding region of transcription factors from yeast and humans and to the product of a homeotic gene from Antirrhinum. The agamous gene therefore probably encodes a transcription factor that regulates genes determining stamen and carpel development in wild-type flowers.

Amino Acid Sequence↗

PubMed1989

Genetic control of flower development.

Flowering plants are the most highly evolved and complex organisms within the plant kingdom. The flower consists of several distinct organ systems that are responsible for higher plant reproduction. Cells within specific floral organs differentiate into spores and gametes required by the plant to complete its life cycle. Flower development represents an excellent model for understanding the molecular and physiological processes that control organ differentiation in higher plants. Rapidly emerging gene tagging procedures are facilitating the isolation of genes that control flower morphogenesis.

Cell Differentiation↗

PubMed1989

Characterization of the glycinin gene family in soybean.

We characterized the structure, organization, and expression of genes that encode the soybean glycinins, a family of storage proteins synthesized exclusively in seeds during embryogenesis. Five genes encode the predominant glycinin subunits found in soybeans, and they have each been cloned, sequenced, and compared. The five genes have diverged into two subfamilies that are designated as Group-I and Group-II glycinin genes. Each glycinin gene contains four exons and three introns like genes that encode related proteins in other legumes. Two other genes have been identified and designated as "glycinin-related" because they hybridize weakly with the five glycinin genes. Although not yet characterized, glycinin-related genes could encode other glycinin subunit families whose members accumulate in minor amounts in seeds. The three Group-I glycinin genes are organized into two chromosomal domains, each about 45 kilobase pairs in length. The two domains have a high degree of homology, and contain at least five genes each that are expressed either in embryos or in mature plant leaves. Gel blot studies with embryo mRNA, as well as transcription studies with 32P-RNA synthesized in vitro from purified embryo nuclei, indicate that glycinin and glycinin-related genes become transcriptionally activated in a coordinated fashion early in embryogenesis, and are repressed coordinately late in seed development. In addition to transcriptional control processes, posttranscriptional events also are involved in regulating glycinin and glycinin-related mRNA levels during embryogenesis.

Amino Acid Sequence↗