Iowa State University

About: Iowa State University is a education organization based out in Ames, Iowa, United States. It is known for research contribution in the topics: Population & Gene. The organization has 50151 authors who have published 107716 publications receiving 3355909 citations. The organization is also known as: Iowa State University of Science and Technology & Iowa State College.

High‐frequency homologous recombination in plants mediated by zinc‐finger nucleases

Abstract: Homologous recombination offers great promise for plant genome engineering. This promise has not been realized, however, because when DNA enters plant cells homologous recombination occurs infrequently and random integration predominates. Using a tobacco test system, we demonstrate that chromosome breaks created by zinc-finger nucleases greatly enhance the frequency of localized recombination. Homologous recombination was measured by restoring function to a defective GUS:NPTII reporter gene integrated at various chromosomal sites in 10 different transgenic tobacco lines. The reporter gene carried a recognition site for a zinc-finger nuclease, and protoplasts from each tobacco line were electroporated with both DNA encoding the nuclease and donor DNA to effect repair of the reporter. Homologous recombination occurred in more than 10% of the transformed protoplasts regardless of the reporter's chromosomal position. Approximately 20% of the GUS:NPTII reporter genes were repaired solely by homologous recombination, whereas the remainder had associated DNA insertions or deletions consistent with repair by both homologous recombination and non-homologous end joining. The DNA-binding domain encoded by zinc-finger nucleases can be engineered to recognize a variety of chromosomal target sequences. This flexibility, coupled with the enhancement in homologous recombination conferred by double-strand breaks, suggests that plant genome engineering through homologous recombination can now be reliably accomplished using zinc-finger nucleases.

Applying Cluster Analysis in Counseling Psychology Research.

Abstract: As a research technique that has grown rapidly in applications in many scientific disciplines, cluster analysis has potential for wider use in counseling psychology research. We begin with a simple example illustrating the clustering approach. Topics covered include the variety of approaches in clustering, the times when cluster analysis may be a choice for analysis, the steps in cluster analysis, the data features, such as level, shape, and scatter, that affect cluster results, alternate clustering methods and evidence indicating which are most effective, and examples of clustering applications in counseling research. Although we make an attempt to provide a comprehensive overview of major issues, the reader is encouraged to consult several good recent publications on the topic that are especially relevant for psychologists. Cluster analysis is a classification technique for forming homogeneous groups within complex data sets. Both the clustering methods and the ways of applying them are extremely diverse. Our purpose in writing this article is to provide an introduction and a road map for applying these techniques productively to research in counseling psychology. The cluster analysis literature is huge, is scattered among many diverse disciplines, and is often arcane. We have made an attempt to cull those aspects most relevant and useful to psychologists from this literature. Most of the discussion in the psychological community about how best to apply cluster analysis to obtain robust, valid, and useful results has taken place within the past 5 years. We seem to be on the verge of a consensus, which has long been needed in an often bewildering field. In the past 30 years, a number of clustering methods, often with their own vocabulary and approaches, have sprouted within a wide variety of scientific disciplines. The earliest sustained applications were in problems of biological classification, within the field called numerical taxonomy (Sokal & Sneath, 1963). Today, clustering is applied to problems as different as the grouping of chemical structures (Massart & Kaufman, 1983) and the classification of helpful and nonhelpful events in counseling (Elliott, 1985). Computerized methods for generating clusters have been developed and made increasingly available over the last decade. Applications of clustering have mushroomed in many disciplines, including the social sciences. In an annual bibliographic search performed by the Classification Society (Day, 1986) 1,166 entries are shown for the 1985 scientific literature alone.

Salt stress responses in Arabidopsis utilize a signal transduction pathway related to endoplasmic reticulum stress signaling.

Abstract: We describe a signaling pathway that mediates salt stress responses in Arabidopsis. The response is mechanistically related to endoplasmic reticulum (ER) stress responses described in mammalian systems. Such responses involve processing and relocation to the nucleus of ER membrane-associated transcription factors to activate stress response genes. The salt stress response in Arabidopsis requires a subtilisin-like serine protease (AtS1P), related to mammalian S1P and a membrane-localized b-ZIP transcription factor, AtbZIP17, a predicted type-II membrane protein with a canonical S1P cleavage site on its lumen-facing side and a b-ZIP domain on its cytoplasmic side. In response to salt stress, it was found that myc-tagged AtbZIP17 was cleaved in an AtS1P-dependent process. To show that AtS1P directly targets AtbZIP17, cleavage was also demonstrated in an in vitro pull-down assay with agarose bead-immobilized AtS1P. Under salt stress conditions, the N-terminal fragment of AtbZIP17 tagged with GFP was translocated to the nucleus. The N-terminal fragment bearing the bZIP DNA binding domain was also found to possess transcriptional activity that functions in yeast. In Arabidopsis, AtbZIP17 activation directly or indirectly upregulated the expression of several salt stress response genes, including the homeodomain transcription factor ATHB-7. Upregulation of these genes by salt stress was blocked by T-DNA insertion mutations in AtS1P and AtbZIP17. Thus, salt stress induces a signaling cascade involving the processing of AtbZIP17, its translocation to the nucleus and the upregulation of salt stress genes.

Widespread horizontal transfer of mitochondrial genes in flowering plants

Abstract: Horizontal gene transfer--the exchange of genes across mating barriers--is recognized as a major force in bacterial evolution. However, in eukaryotes it is prevalent only in certain phagotrophic protists and limited largely to the ancient acquisition of bacterial genes. Although the human genome was initially reported to contain over 100 genes acquired during vertebrate evolution from bacteria, this claim was immediately and repeatedly rebutted. Moreover, horizontal transfer is unknown within the evolution of animals, plants and fungi except in the special context of mobile genetic elements. Here we show, however, that standard mitochondrial genes, encoding ribosomal and respiratory proteins, are subject to evolutionarily frequent horizontal transfer between distantly related flowering plants. These transfers have created a variety of genomic outcomes, including gene duplication, recapture of genes lost through transfer to the nucleus, and chimaeric, half-monocot, half-dicot genes. These results imply the existence of mechanisms for the delivery of DNA between unrelated plants, indicate that horizontal transfer is also a force in plant nuclear genomes, and are discussed in the contexts of plant molecular phylogeny and genetically modified plants.

Laser-Capture Microdissection, a Tool for the Global Analysis of Gene Expression in Specific Plant Cell Types: Identification of Genes Expressed Differentially in Epidermal Cells or Vascular Tissues of Maize

Abstract: Laser-capture microdissection (LCM) allows for the one-step procurement of large homogeneous populations of cells from tissue sections. In mammals, LCM has been used to conduct cDNA microarray and proteomics studies on specific cell types. However, LCM has not been applied to plant cells, most likely because plant cell walls make it difficult to separate target cells from surrounding cells and because ice crystals can form in the air spaces between cells when preparing frozen sections. By fixing tissues, using a cryoprotectant before freezing, and using an adhesive-coated slide system, it was possible to capture large numbers (>10,000) of epidermal cells and vascular tissues (vascular bundles and bundle sheath cells) from ethanol:acetic acid–fixed coleoptiles of maize. RNA extracted from these cells was amplified with T7 RNA polymerase and used to hybridize a microarray containing ∼8800 maize cDNAs. Approximately 250 of these were expressed preferentially in epidermal cells or vascular tissues. These results demonstrate that the combination of LCM and microarrays makes it feasible to conduct high-resolution global gene expression analyses of plants. This approach has the potential to enhance our understanding of diverse plant cell type–specific biological processes.