Tomato resistance to Alternaria stem canker: localization in host genotypes and functional expression compared to non-host resistance

Summary The Alternaria stem canker resistance locus (Asc-locus), involved in resistance to the fungal pathogen Alternaria alternata f. sp. lycopersici and in insensitivity to host-specific toxins (AAL-toxins) produced by the pathogen, was genetically mapped on the tomato genome. Susceptibility and resistance were assayed by testing a segregating F₂ population for sensitivity to AAL-toxins in leaf bioassays. Linkage was observed to phenotypic markers solanifolium and sunny, both on chromosome 3. For the Asc-locus, a distance of 18 centiMorgan to solanifolium was calculated, corresponding to position 93 on chromosome 3. This map position of the resistance locus turned out to be the same in three different resistant tomato accessions, one Dutch and two American, that are at least 40 years apart. AAL-toxin sensitivity in susceptible and resistant tomato genotypes was compared with AAL-toxin sensitivity in a non-host Nicotiana tabacum during different levels of plant cell development. In susceptible and resistant tomato genotypes, inhibitory effects were demonstrated at all levels, except for leaves of resistant genotypes. However, during pollen and root development, inhibitory effects on susceptible genotypes were larger than on resistant genotypes. In the non-host Nicotiana tabacum, hardly any effects of AAL-toxins were demonstrated. Apparently, a cellular target site is present in tomato, but not in Nicotiana tabacum. It was concluded that three levels of AAL-toxin sensitivity exist: (1) a susceptible host sensitivity, (2) a resistant host sensitivity, (3) a non-host sensitivity, and that the resistance mechanism operating in tomato is different from that operating in Nicotiana tabacum.     

Method to estimate genotype probabilities at individual loci in farm livestock

Summary A Bayesian method to estimate genotype probabilities at a single locus using information on the individual and all its relatives and their mates has been developed. The method uses data over several generations, can deal with large numbers of individuals in large livestock families and allows for missing information. It can be extended to multiple alleles and can be used for autosomal or sex-linked loci. The allele frequencies and the form of expression (dominance, penetrance) must be specified. An algorithm using the method and involving an iterative procedure has been developed to calculate the genotype probabilities for practical use in livestock breeding. The method and algorithm were used to determine the accuracy of estimating genotype probabilities of sires for a female sex-limited trait, such as genetic variants of milk proteins. Data were similated and genotype probabilities estimated for 100 sires (20 replicates) with 3, 6 and 12 female offspring per sire, for different population frequencies, for additive and dominance gene action and for variable genotypic expression. Such simulation is useful in the design of testing systems for the use of information on specific genetic loci in selection.Prepared during a leave at Centre for Genetic Improvement of Livestock, Guelph, Canada     

A major histocompatibility locus in fish: serological identification and segregation of transplantation antigens in the common carp (Cyprinus carpio L.)

In this study, experiments are described that were designed to investigate whether fish have an immune regulatory systems similar to the major histocompatibility complex (MHC) in higher vertebrate species. From combinations of gynogenetic carp showing either slow of fast rejection of skin transplants, the latter were chosen for alloantiserum production by hyperimmunization with peripheral blood leucocytes. The resulting alloantisera were analyzed for hemagglutinating reactivity with gynogenetic siblings and proved to be operationally monoscpecific in absorption experiments. The serologically determined carp erythrocyte specificites were shown to correspond to two codominantly expressed allelic products of a single locus and were designated K1 and K2, respectively. Flow cytometer analysis revealed that the same products are also present on leucocytes from peripheral blood, thymus, spleen, and pronephros.K1-andK2-homozygous second-generation gynogenetic siblings were used to study the histocompatibiligy nature of the K locus products. Skin transplants between K-allogeneic gynogenetic siblings were rejected significantly faster than within K-syngeneic combinations. Taken together, these data suggest that theK locus incorporates MHC class I-like characteristics.     

Analysis of the HLA-A10-crossreacting group of antigens by one-dimensional isoelectric focusing

The antigens belonging to the HLA-A10 group, HLA-A25, -A26, -Aw34, and -Aw66, have been characterized serologically during the International Histocompatibility Workshops. However, it remains difficult to discriminate between the HLA-A26 antigen on the one hand and the HLA-Aw34 and -Aw66 antigens on the other on the basis of serology. In this paper, we compare the serologically defined antigens with the data obtained by one-dimensional isoelectric focusing. The results indicate that the serologically well-defined HLA-A25 antigen cannot be discriminated from the HLA-A26 antigen by one-dimensional isoelectric focusing. In contrast, this technique can indeed be used to discriminate between HLA-A26, -Aw34 and -Aw66 antigens. In addition, the biochemical analysis suggests further heterogeneity of the HLA-Aw34 antigen. This antigen can be subdivided into three variants.     

Transient expression of the proto-oncogene int-1 during differentiation of P19 embryonal carcinoma cells.

In mouse embryos, the int-1 proto-oncogene is transiently expressed in areas of the developing neural system. Retinoic acid-treated P19 embryonal carcinoma cells have often been used as an in vitro model for the molecular basis of neural development. We shown here that int-1 is transiently expressed in differentiated P19 cells. The time course and retinoic acid dose dependence of int-1 expression suggest that the gene is specifically expressed during early neural differentiation. P19 cells may be a useful model to assist in the study, at the cellular level, of the role of int-1 in neural development.     

Accumulation of viruslike particles in a yeast mutant lacking a mitochondrial pore protein.

The lack of mitochondrial porin is not lethal in Saccharomyces cerevisiae, but it impairs some respiratory functions and, therefore, growth on nonfermentable carbon sources such as glycerol. However, after a lag phase porinless mutant cells adapt to growth on glycerol, accumulating large amounts of an 86-kilodalton (kDa) protein (M. Dihanich, K. Suda, and G. Schatz, EMBO J. 6:723-728, 1987) and of a 5-kilobase RNA. Immunogold labeling localized the 86 kDa-protein exclusively to the cytosol fraction, although most of it cosedimented with the microsome fraction in earlier cell fractionations. This discrepancy was resolved when the 86-kDa protein was identified as the major coat protein in viruslike particles (VLPs) which is encoded by a double-stranded RNA (L-A RNA). Elimination of VLPs in the original porinless strain by introduction of the mak10 or the mak3 mutation increased the respiratory defect and prolonged its lag phase on nonfermentable carbon sources. The fact that the simultaneous loss of VLPs and respiratory functions are the introduction of mak10 or mak3 occurred even in some porin-containing wild-type strains suggests that there is a link between VLP and mitochondrial functions.     

Opinion

The Editors of Letters in Applied Microbiology will, at their discretion, publish invited and submitted 'Opinions' on subjects in the general area of Applied Microbiology. They will not be subjected to the normal refereeing procedures and reprints will not be provided. The 'Opinions' will not necessarily represent the views of the Society for Applied Bacteriology or of the Editors. The Editors may invite or readers may submit 'Responses' to published 'Opinions' , provided that they are not merely polemics, and these will also be published at the discretion of the Editors. 'Responses' will be treated precisely like 'Opinions'. They should clearly indicate, in their first sentence, the 'Opinion' to which they are a response.     

DNA-binding domain of human c-Myc produced in Escherichia coli.

We have identified the domain of the human c-myc protein (c-Myc) produced in Escherichia coli that is responsible for the ability of the protein to bind sequence-nonspecific DNA. Using analysis of binding of DNA by proteins transferred to nitrocellulose, DNA-cellulose chromatography, and a nitrocellulose filter binding assay, we examined the binding properties of c-Myc peptides generated by cyanogen bromide cleavage, of mutant c-Myc, and of proteins that fuse portions of c-Myc to staphylococcal protein A. The results of these analyses indicated that c-Myc amino acids 265 to 318 were responsible for DNA binding and that other regions of the protein (including a highly conserved basic region and a region containing the leucine zipper motif) were not required. Some mutant c-Mycs that did not bind DNA maintained rat embryo cell-cotransforming activity, which indicated that the c-Myc property of in vitro DNA binding was not essential for this activity. These mutants, however, were unable to transform established rat fibroblasts (Rat-1a cells) that were susceptible to transformation by wild-type c-Myc, although this lack of activity may not have been due to their inability to bind DNA.