Mutant

About: Mutant is a research topic. Over the lifetime, 74520 publications have been published within this topic receiving 3477079 citations.

Gene-for-gene disease resistance without the hypersensitive response in Arabidopsis dnd1 mutant

Abstract: The cell death response known as the hypersensitive response (HR) is a central feature of gene-for-gene plant disease resistance. A mutant line of Arabidopsis thaliana was identified in which effective gene-for-gene resistance occurs despite the virtual absence of HR cell death. Plants mutated at the DND1 locus are defective in HR cell death but retain characteristic responses to avirulent Pseudomonas syringae such as induction of pathogenesis-related gene expression and strong restriction of pathogen growth. Mutant dnd1 plants also exhibit enhanced resistance against a broad spectrum of virulent fungal, bacterial, and viral pathogens. The resistance against virulent pathogens in dnd1 plants is quantitatively less strong and is differentiable from the gene-for-gene resistance mediated by resistance genes RPS2 and RPM1. Levels of salicylic acid compounds and mRNAs for pathogenesis-related genes are elevated constitutively in dnd1 plants. This constitutive induction of systemic acquired resistance may substitute for HR cell death in potentiating the stronger gene-for-gene defense response. Although cell death may contribute to defense signal transduction in wild-type plants, the dnd1 mutant demonstrates that strong restriction of pathogen growth can occur in the absence of extensive HR cell death in the gene-for-gene resistance response of Arabidopsis against P. syringae.

The beige mutation in the mouse selectively impairs natural killer cell function.

Abstract: GERM LINE mutations affecting defined cell populations are often valuable tools in elucidating the function of these cells in complex biological systems such as tumour rejection. We report here that a mutant gene in the mouse called beige (bgJ), leads to a complete and selective impairment of naturally occurring killer lymphocytes, whereas all other forms of cell-mediated lysis are apparently normal. The defective gene product may lie within the lytic pathway subsequent to tumour cell contact. Because many cell types, including natural killer (NK) cells, T cells and macrophages, may be involved in tumour resistance in vivo1, these mice will provide a critical test of the hypothesis that it is NK cells which provide a first line of defence against neoplasia2. It is likely that this mutant will be invaluable for further investigations in tumour immunology just as the nude mouse has been indispensable in evaluating the role of thethymus in the development of the T-lymphoid system and the role of T cells in the rejection of tumours.

On Some Principles Governing Molecular Evolution

Abstract: The following five principles were deduced from the accumulated evidence on molecular evolution and theoretical considerations of the population dynamics of mutant substitutions: (i) for each protein, the rate of evolution in terms of amino acid substitutions is approximately constant/site per year for various lines, as long as the function and tertiary structure of the molecule remain essentially unaltered (ii) Functionally less important molecules or parts of a molecule evolve (in terms of mutant substitutions) faster than more important ones (iii) Those mutant substitutions that disrupt less the existing structure and function of a molecule (conservative substitutions) occur more frequently in evolution than more disruptive ones (iv) Gene duplication must always precede the emergence of a gene having a new function (v) Selective elimination of definitely deleterious mutants and random fixation of selectively neutral or very slightly deleterious mutants occur far more frequently in evolution than positive Darwinian selection of definitely advantageous mutants