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Daphne Preuss

Publications and source records attributed to Daphne Preuss.

9 recordsLinked to original sources
PubMed2003

Strand-biased DNA methylation associated with centromeric regions in Arabidopsis.

The Arabidopsis genome project assembled 15 megabases of heterochromatic sequence, facilitating investigations of heterochromatin assembly, maintenance, and structure. In many species, large quantities of methylcytosine decorate heterochromatin; these modifications are typically maintained by methyltransferases that recognize newly replicated hemimethylated DNA. We assessed the extent and patterns of Arabidopsis heterochromatin methylation by amplifying and sequencing genomic DNA treated with bisulfite, which converts cytosine, but not methylcytosine, to uracil. This survey revealed unexpected asymmetries in methylation patterns, with one helix strand often exhibiting higher levels of methylation. We confirmed these observations both by immunoprecipitating methylated DNA strands and by restriction enzyme digestion of amplified, bisulfite-treated DNA. We also developed a primer-extension assay that can monitor the methylation status of an entire chromosome, demonstrating that strand-specific methylation occurs predominantly in the centromeric regions. Conventional models for methylation maintenance do not explain these unusual patterns; instead, new models that allow for strand specificity are required. The abundance of Arabidopsis strand-specific modifications points to their importance, perhaps as epigenetic signals that mark the heterochromatic regions that confer centromere activity.

Arabidopsis↗
PubMed2003

Pollen tube growth and guidance is regulated by POP2, an Arabidopsis gene that controls GABA levels.

During angiosperm reproduction, pollen grains form a tube that navigates through female tissues to the micropyle, delivering sperm to the egg; the signals that mediate this process are poorly understood. Here, we describe a role for gamma-amino butyric acid (GABA) in pollen tube growth and guidance. In vitro, GABA stimulates pollen tube growth, although vast excesses are inhibitory. The Arabidopsis POP2 gene encodes a transaminase that degrades GABA and contributes to the formation of a gradient leading up to the micropyle. pop2 flowers accumulate GABA, and the growth of many pop2 pollen tubes is arrested, consistent with their in vitro GABA hypersensitivity. Some pop2 tubes continue to grow toward ovules, yet they are misguided, presumably because they target ectopic GABA on the ovule surface. Interestingly, wild-type tubes exhibit normal growth and guidance in pop2 pistils, perhaps by degrading excess GABA and sharpening the gradient leading to the micropyle.

Arabidopsis↗
PubMed2003

On your mark, get set, GROW! LePRK2-LAT52 interactions regulate pollen tube growth.

Recent discoveries show that LAT52 and LePRK2, two pollen-specific proteins, interact in what might be an autocrine signaling system. This exciting finding indicates that successful fertilization requires ligand-receptor kinase signals that regulate pollen-tube growth. The stage is now set to identify other components of this pathway and to explore their connections with the many signals exchanged between pollen and pistil.

Fertility↗
PubMed2003

Centromere satellites from Arabidopsis populations: maintenance of conserved and variable domains.

The rapid evolution of centromere sequences between species has led to a debate over whether centromere activity is sequence-dependent. The Arabidopsis thaliana centromere regions contain approximately 20,000 copies of a 178-bp satellite repeat. Here, we analyzed satellites from 41 Arabidopsis ecotypes, providing the first broad population survey of satellite variation within a species. We found highly conserved segments and consistent sequence lengths in the Arabidopsis satellites and in the published collection of human alpha-satellites, supporting models for a functional role. Despite this conservation, polymorphisms are significantly enriched at some sites, yielding variation that could restrict binding proteins to a subset of repeat monomers. Some satellite regions vary considerably; at certain bases, consensus sequences derived from each ecotype diverge significantly from the Arabidopsis consensus, indicating substitutions sweep through a genome in less than 5 million years. Such rapid changes generate more variation within the set of Arabidopsis satellites than in genes from the chromosome arms or from the recombinationally suppressed centromere regions. These studies highlight a balance between the mechanisms that maintain particular satellite domains and the forces that disperse sequence changes throughout the satellite repeats in the genome.

Arabidopsis↗
PubMed2002

Plotting a course: multiple signals guide pollen tubes to their targets.

Pollen plays a critical role in the life cycle of all flowering plants, generating a polarized pollen tube that delivers sperm to the eggs in the interior of the flower. Pollen tubes perceive multiple extracellular signals during their extended growth through different floral environments; these environments discriminate among pollen grains, allowing only those that are appropriately recognized to invade. The phases of pollen tube growth include interactions that establish pollen polarity, entry of pollen tubes into female cell walls, and adhesion-based pollen tube motility through a carbohydrate-rich matrix. Recent studies have identified cells within the female germ unit as important sources of pollen guidance cues. Other signals undoubtedly exist, and their discovery will require genetic screens that target diploid tissues as well as haploid male and female cells.

Gene Expression Regulation, Plant↗
PubMed2002

Characterization of T-DNA insertion sites in Arabidopsis thaliana and the implications for saturation mutagenesis.

A key component of a sound functional genomics infrastructure is the availability of a knockout mutant for every gene in the genome. A fruitful approach to systematically knockingout genes in the plant Arabidopsis thaliana has been the use of transferred-DNA (T-DNA) from Agrobacterium tumefaciens as an insertional mutagen. One of the assumptions underlying the use of T-DNA as a mutagen is that the insertion of these DNA elements into the Arabidopsis genome occurs at randomly selected locations. We have directly investigated the distribution of T-DNA insertions sites in populations of transformed Arabidopsis using two different approaches. To begin with, we utilized a polymerase chain reaction (PCR) procedure to systematically catalog the precise locations of all the T-DNA elements inserted within a 65 kb segment of chromosome IV. Of the 47 T-DNA insertions identified, 30% were found within the coding regions of genes. We also documented the insertion of T-DNA elements within the centromeric region of chromosome IV. In addition to these targeted T-DNA screens, we also mapped the genomic locations of 583 randomly chosen T-DNA elements by sequencing the genomic DNA flanking the insertion sites from individual T-DNA-transformed lines. 35% of these randomly chosen T-DNA insertions were located within the coding regions of genes. For comparison, coding sequences account for 44% of the Arabidopsis genome. Our results demonstrate that there is a small bias towards recovering T-DNA insertions within intergenic regions. However, this bias does not limit the utility of T-DNA as an effective insertional mutagen for use in reverse-genetic strategies.

Arabidopsis↗