Albert H. Ellingboe

Genetical Aspects of Active Defence

I find myself in a rather uncomfortable position in presenting this paper. The reason for this is that what I have to say does not support much of the speculation and dogma that has been presented in preceding papers. I feel like a non-believer in a congregation of believers. The belief seems to be that specificity of the interactions between host and parasite, and the restriction of development of the pathogen, are controlled by compounds not produced by transcription and translation. This I find difficult to reconcile with the known genetics of interactions. What I will try to do, therefore, is to present the kinds of results obtained from studies of the inheritance of genetic variability in host-parasite interactions, then proceed to describe some models and give examples of what the genetics tells me about those models of interactions, and conclude with some examples of uses of genetic arguments in studies of host-parasite interactions.

Reduction of transpiration from wheat caused by germinating conidia of Erysiphe graminis f. sp. tritici

Abstract Detached wheat leaves, 1 to 6 h after inoculation with viable conidia of Erysiphe graminis f. sp. trici , took up 25 and 20% less 32 P and 35 S, respectively, than did non-inoculated leaves. The transpiration rate of inoculated leaves was 25% less than non-inoculated leaves. Reduced transpiration occurred with both compatible and incompatible parasite/host genotypes. Relative diffusion resistances were higher for inoculated plants than for non-inoculated plants. U.V.-killed spores, chalk dust, carborundum, Puccinia recondita uredospores, and Helminthosporium victoriae conidia heavily dusted onto leaves did not reduce 32 P uptake. Under conditions of these experiments, the uredospores of P. recondita and the conidia of H. victoriae did not germinate.

Genetic control of 32P transfer from wheat to Erysiphe graminis f. sp. tritici during primary infection

Abstract Environmental conditions necessary for synchronous development of Erysiphe graminis D.C. f. sp. tritici Em. Marchal during primary infection of wheat were shown to affect the amount of 32P taken up and translocated to the epidermis of excised leaves placed in a 32P solution. Light increased transpiration, the amount of 32P taken up by the leaves and the amount of 32P transferred to the parasite. Rates of 32P transfer from host to parasite were determined for compatible and incompatible parasite-host interactions during primary infection. Transfer rate reflected the relative compatibility of the host-parasite interaction studied. Interactions with little fungal development had lower total rates ou transfer than did compatible interactions. However, when transfer was expressed as UP transferred per successful primary infection, the successful parasite units involved in incompatible interactions obtained 32P at a greater rate than did parasite units in compatible interactions.

Isolation of functional ribosomes and polysomes from lyophilized fungi

Abstract Functional monosomes and polysomes were readily isolated from lyophilized mycelia and spores of the tetrapolar basidiomycetes Schizophyllum commune and Coprinus lagopus. 1. 1. Monosomes having sedimentation properties similar to rabbit reticulocyte monosomes predominate in these ribosomal preparations. 2. 2. Polysomes of dimer, trimer, and tetramer size are consistently present. The polysomes are stable at low Mg2+ concentrations and are sensitive to ribonuclease treatment. 3. 3. The ribosomes are functional in a cell-free protein synthesizing system containing no exogenous mRNA. The isolation of intact polysomes from the material lyophilized prior to grinding is considered significant because of the advantages of this technique to molecular studies on organisms with resistant cell walls and because of the indication that lyophilization has little effect on the functional integrity of the polysome-mRNA complex.

High resolution two-dimensional electrophoresis of protein from congenic wheat lines differing by single resistance genes

Two methods were developed for the extraction of proteins from green wheat leaves. The methods result in distinct, highly reproducible patterns of polypeptides when separated by two-dimensional electrophoresis. Interference due to phenolic compounds and proteinases was minimized by these methods, and over 300 polypeptides were observed when visualized with Coomassie blue stain. Comparisons of 12 different congenic host lines, each differing by a single gene for resistance to Erysiphe graminis f. sp. tritici (Pm isolines), failed to reveal any differences in polypeptide mobility which could be attributed to, or associated with, a gene for resistance. Some seedlings of “Chancellor” wheat, the common background parent cultivar from which all of the Pm lines were derived, exhibited a unique polypeptide variant. The variant polypeptide was not found in all seedlings of “Chancellor”, nor was it found in any of the Pm lines tested. The variant polypeptide appears to reflect a change in molecular weight from about 63 000 to about 68 000, with a very slight change in charge (pI of about 4). The variant polypeptide is among the 300 most visible polypeptides in seedling extracts that were subjected to electrophoresis and stained with silver. Thus, the variant polypeptide appears to be made in a large number of copies. Chancellor appears to be a mixture of the original type and a variant type which appeared subsequent to the breeding of the Pm lines.

Cell wall composition of near isogenic wheat lines carrying genes for resistance to Erysiphe graminis f. sp. Tritici

Abstract Cell wall composition of near isogenic wheat ( Triticum aestivum L. em Thell) lines were compared during the initial growth period of 5–9 days. The lines could not be distinguished in terms of hydroxyproline arabinoside (Hyp-ara) profiles, amino acids and neutral sugars composition and levels. This tends to support the idea that the hosts resistance genes are not expressed as major constituents of the cell wall.

Effect of environmental conditions on 35S uptake by Triticum aestivum and transfer to Erysiphe graminis f sp. tritici during primary infection

Abstract Light is necessary at specific times during primary infection for synchronous development of Erysiphe graminis f. sp. tritici on wheat. The effects of the environmental conditions on the uptake and translocation to the epidermis of 35 S and subsequent transfer to the parasite in the inoculated host were examined. Inoculated wheat plants were cut and fed 35 S for various 5-h periods beginning 1 to 21 h after inoculation. Radioactivity was determined in 1-cm leaf sections, epidermal strips, and the fungus on the leaf surface. Leaf sections and epidermal strips incubated in light yielded 20 and 4·5 × 10 4 ct/min, respectively, which is more than twice the ct/min obtained for plants incubated in darkness. Radioactivity in the fungus on the leaf surface ranged from background to 2100 ct/min/10 000 spores applied to the leaf. The rates of 35 S transfer from host to parasite were affected by the amount of tracer absorbed by the plant, the stage of development of the parasite during primary infection, and by parasite/host genes for compatibility. There were differences in rates of 35 S transfer between four different parasite/host genotypes for incompatibility ( P1/Pm1, P2/Pm2, P3a/Pm3a and P4/Pm4 ) after considering the amount of label in the host epidermis. Rates of 35 S transfer from host to parasite during primary infection are greater at 18 and 20 h after inoculation than at later times. Haustoria are not fully developed at these hours.

The induction and characterization of recessive suppressors of arg-2 in Schizophyllum commune

SummaryGenetic analyses have been made to detect recessive suppressor mutations in eight prototrophic strains derived by treating an arginine dependent strain with hydroxylamine. The results indicate that one strain possesses a recessive suppressor, su-1, which maps outside the arg-2 locus and is capable of suppressing auxotrophy conferred by the arg-2 mutation. This suppressor is incapable of suppressing auxotrophy conferred by eight other loci. Prototrophy in the remaining seven strains resulted from either intragenic suppression, reversion, or from a suppressor mutation that is closely linked to the arg-2 locus. The results of heterokaryotic allelic tests with the seven strains indicate that the mutation to prototrophy is recessive.

Isolation and characterization of compatible diploids of Schizophyllum commune

SummaryCommon-AB diploids with several heterozygous biochemical markers were mated with appropriately marked haploid strains of S. commune in an effort to obtain compatible, common-A, and common-B diploid progeny with biochemical markers identical to those of the common-AB parent. The spores from these crosses were germinated on minimal medium. Five compatible diploids, but no common-A or common-B diploids, marked as desired, were isolated by this method. Two possessed some dikaryotic cells and two had many dikaryotic cells. One of the latter was shown to have peculiar behaviour associated with one of its B mating-type factors.

Somatic recombination in the common-AB diploid of Schizophyllum commune.

SummaryA recessive suppressor, su-1, of arg-2 was used to detect somatic recombination in common-AB diploids of S. commune. Recombinants were recovered from dense, fastgrowing sectors on arginine-deficient medium. The majority of spontaneous recombinants (129/154) recovered in this study were apparently haploid. Strains which scored as aneuploid and diploid were also recovered and analyzed. Genetic analysis of spontaneous recombinants indicated that crossing over is rare and that haploidization very likely proceeds via stages of aneuploidy. No increase in the frequency of crossing over was detected in recombinants derived following treatment with UV light. The preliminary results favor a parasexual mechanism of recombination in common-AB diploids.