Showing papers by "Detlef Weigel published in 2002"

Arabidopsis : a laboratory manual

Abstract: Chapter 1: How to grow Arabidopsis Chapter 2: Obtaining mutants Chapter 3: Genetic analysis of mutants Chapter 4: How to analyze a mutant phenotypically Chapter 5: How to transform Arabidopsis Chapter 6: How to isolate a gene defined by a mutation Chapter 7: How to study gene expression Chapter 8: How to study gene function Appendix 1: Where to find information on Arabidopsis Appendix 2: Critical chi-squared values Appendix 3: Cautions Appendix 4: Suppliers

The extent of linkage disequilibrium in Arabidopsis thaliana

Abstract: Linkage disequilibrium (LD), the nonrandom occurrence of alleles in haplotypes, has long been of interest to population geneticists. Recently, the rapidly increasing availability of genomic polymorphism data has fueled interest in LD as a tool for fine-scale mapping, in particular for human disease loci(1). The chromosomal extent of LD is crucial in this context, because it determines how dense a map must be for associations to be detected and, conversely, limits how finely loci may be mapped(2). Arabidopsis thaliana is expected to harbor unusually extensive LD because of its high degree of selfing(3). Several polymorphism studies have found very strong LD within individual loci, but also evidence of some recombination(4-6). Here we investigate the pattern of LD on a genomic scale and show that in global samples, LD decays within approximately 1 cM, or 250 kb. We also show that LD in local populations may be much stronger than that of global populations, presumably as a result of founder events. The combination of a relatively high level of polymorphism and extensive haplotype structure bodes well for developing a genome-wide LD map in A. thaliana.

Stem cells that make stems

Abstract: Plant stem cells, contained in specialized structures called meristems, have amazing regenerative powers. They enable plants to grow and produce new organs throughout lifetimes that can span hundreds of years.

Interaction of LEAFY, AGAMOUS and TERMINAL FLOWER1 in maintaining floral meristem identity in Arabidopsis

Abstract: The Arabidopsis transcription factor LEAFY acts upstream of homeotic genes such as AGAMOUS to confer floral identity on meristems that arise after the transition to reproductive development. Compared to the genetic circuitry regulating the establishment of floral meristem identity, little is known about its maintenance. Previous experiments with leafy heterozygous plants and agamous mutants grown in conditions that reduce the floral inductive stimulus have shown that both genes are required to prevent reversion of floral to inflorescence meristems. Here, we present evidence that LEAFY maintains floral meristem identity independently of AGAMOUS, and that the primary role of LEAFY is either direct repression of shoot identity genes or repression of an intermediate factor that activates shoot identity genes. The latter conclusions were deduced from the phenotypes conferred by a gain-of-function transgene, LEAFY:VP16, that appears to act as a dominant negative, or antimorphic, allele during maintenance of floral meristem identity. These observations contrast with previous findings that LEAFY acts as a direct activator of floral homeotic genes, supporting the hypothesis that the transcriptional activity of LEAFY is dependent on specific co-regulators.

Quantitative Trait Loci Controlling Light and Hormone Response in Two Accessions of Arabidopsis thaliana

Abstract: We have mapped quantitative trait loci (QTL) responsible for natural variation in light and hormone response between the Cape Verde Islands (Cvi) and Landsberg erecta (Ler) accessions of Arabidopsis thaliana using recombinant inbred lines (RILs). Hypocotyl length was measured in four light environments: white, blue, red, and far-red light and in the dark. In addition, white light plus gibberellin (GA) and dark plus the brassinosteroid biosynthesis inhibitor brassinazole (BRZ) were used to detect hormone effects. Twelve QTL were identified that map to loci not previously known to affect light response, as well as loci where candidate genes have been identified from known mutations. Some QTL act in all environments while others show genotype-by-environment interaction. A global threshold was established to identify a significant epistatic interaction between two loci that have few main effects of their own. LIGHT1, a major QTL, has been confirmed in a near isogenic line (NIL) and maps to a new locus with effects in all light environments. The erecta mutation can explain the effect of the HYP2 QTL in the blue, BRZ, and dark environments, but not in far-red. LIGHT2, also confirmed in an NIL, has effects in white and red light and shows interaction with GA. The phenotype and map position of LIGHT2 suggest the photoreceptor PHYB as a candidate gene. Natural variation in light and hormone response thus defines both new genes and known genes that control light response in wild accessions.

Signaling in plants by intercellular RNA and protein movement

Abstract: Plants and animals have had about 1.6 billion years—the time that has passed since they diverged from their last unicellular ancestor—to evolve different mechanisms for solving unique problems of development and intercellular signaling. As an example, plant cells are separated from each other by a substantial extracellular matrix, the cell wall. Although the cell wall is not impervious, it is likely to hinder cell-to-cell communication. Moreover, because plant cells cannot migrate during development, location, instead of lineage, is the primary determinant of cell fate in plants, making communication over both long and short distances essential for the coordination of plant growth. It appears that plants have significantly overcome the downside of having a cell wall by forming channels between cells to allow the transit of signaling and other important molecules. Plants may even be considered as supracellular organisms, in that whole tissues are symplastically connected. The channels that connect plant cells are called plasmodesmata (PD), and their investigation offers tantalizing clues as to how plant cells may use them to communicate with each other and to coordinate development. Although once seen as constricted channels through which only molecules <1 kD in size could pass (Terry and Robards 1987; Burnell 1988), PD have recently been shown to be far more dynamic and allow passage of both proteins and nucleic acids. Other findings, such as the observation that transcription factors can move between cells, and that RNA movement may be behind a range of long-distance signals in plants, raise further questions regarding a regulatory role of PD in development. Because of the importance of PD, we first summarize what we know about them, and then go on to discuss intercellular movement of proteins and RNA in general.

Independent Control of Gibberellin Biosynthesis and Flowering Time by the Circadian Clock in Arabidopsis

Abstract: Flowering of the facultative long-day plant Arabidopsis is controlled by several endogenous and environmental factors, among them gibberellins (GAs) and day length. The promotion of flowering by long days involves an endogenous clock that interacts with light cues provided by the environment. Light, and specifically photoperiod, is also known to regulate the biosynthesis of GAs, but the effects of GAs and photoperiod on flowering are at least partially separable. Here, we have used a short-period mutant, toc1, to investigate the role of the circadian clock in the control of flowering time by GAs and photoperiod. We show that toc1 affects expression of several floral regulators and a GA biosynthetic gene, but that these effects are independent.

Ectopic expression of SUPERMAN suppresses development of petals and stamens

Abstract: The floral regulatory gene SUPERMAN (SUP) encodes a C2H2 type zinc finger protein that is required for maintaining boundaries between floral organs in Arabidopsis. It has been proposed that the main function of SUP is to balance cell proliferation in the third and fourth whorl of developing flowers, thereby maintaining the boundaries between the two whorls. To gain further insight into the function of SUP, we have ectopically expressed SUP using the promoter of APETALA1 (AP1), a gene that is initially expressed throughout floral meristems and later becomes restricted to the first and second whorls. Flowers of AP1::SUP plants have fewer floral organs, consistent with an effect of SUP on cell proliferation. In addition, the AP1::SUP transgene caused the conversion of petals to sepals and suppressed the development of stamens. The expression of the B function homeotic gene APETALA3 (AP3) and its regulator UNUSUAL FLORAL ORGANS (UFO) were delayed and reduced in AP1::SUP flowers. However, SUP does not act merely through UFO, as constitutive expression of UFO did not rescue the defects in petal and stamen development in AP1::SUP flowers. Together, these results suggest that SUP has both indirect and direct effects on the expression of B function homeotic genes.