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L M Geletka

Publications and source records attributed to L M Geletka.

6 recordsLinked to original sources
PubMed2000

Using chimeric hypoviruses to fine-tune the interaction between a pathogenic fungus and its plant host.

Infectious cDNA clones of mild (CHV1-Euro7) and severe (CHV1-EP713) hypovirus strains responsible for virulence attenuation (hypovirulence) of the chestnut blight fungus Cryphonectria parasitica were used to construct viable chimeric viruses. Differences in virus-mediated alterations of fungal colony morphology, growth rate, and canker morphology were mapped to a region of open reading frame B extending from nucleotides 2,363 to 9, 904. By swapping domains within this region, it was possible to generate chimeric hypovirus-infected C. parasitica isolates that exhibited a spectrum of defined colony and canker morphologies. Several severe strain traits were observed to be dominant. It was also possible to uncouple the severe strain traits of small canker size and suppression of asexual sporulation. For example, fungal isolates infected with a chimera containing nucleotides 2363 through 5310 from CHV1-Euro7 in a CHV1-713 background formed small cankers that were similar in size to that caused by CHV1-EP713-infected isolates but with the capacity for producing asexual spores at levels approaching that observed for fungal isolates infected with the mild strain. These results demonstrate that hypoviruses can be engineered to fine-tune the interaction between a pathogenic fungus and its plant host. The identification of specific hypovirus domains that differentially contribute to canker morphology and sporulation levels also provides considerable utility for continuing efforts to enhance biological control potential by balancing hypovirulence and ecological fitness.

Ascomycota↗
PubMed2000

Essential and dispensable virus-encoded replication elements revealed by efforts To develop hypoviruses as gene expression vectors.

We have investigated whether hypoviruses, viral agents responsible for virulence attenuation (hypovirulence) of the chestnut blight fungus Cryphonectria parasitica, could serve as gene expression vectors. The infectious cDNA clone of the prototypic hypovirus CHV1-EP713 was modified to generate 20 different vector candidates. Although transient expression was achieved for a subset of vectors that contained the green fluorescent protein gene from Aequorea victoria, long-term expression (past day 8) was not observed for any vector construct. Analysis of viral RNAs recovered from transfected fungal colonies revealed that the foreign genes were readily deleted from the replicating virus, although small portions of foreign sequences were retained by some vectors after months of replication. However, the results of vector viability and progeny characterization provided unexpected new insights into essential and dispensable elements of hypovirus replication. The N-terminal portion (codons 1 to 24) of the 5'-proximal open reading frame (ORF), ORF A, was found to be required for virus replication, while the remaining 598 codons of this ORF were completely dispensable. Substantial alterations were tolerated in the pentanucleotide UAAUG that contains the ORF A termination codon and the overlapping putative initiation codon of the second of the two hypovirus ORFs, ORF B. Replication competence was maintained following either a frameshift mutation that caused a two-codon extension of ORF A or a modification that produced a single-ORF genomic organization. These results are discussed in terms of determinants of hypovirus replication, the potential utility of hypoviruses as gene expression vectors, and possible mechanisms by which hypoviruses recognize and delete foreign sequences.

Amino Acid Sequence↗
PubMed1995

The replication of a necrogenic cucumber mosaic virus satellite is temperature-sensitive in tomato.

Lethal necrosis development in tomato plants infected with cucumber mosaic virus (CMV) strain D containing the necrogenic satellite D-CARNA 5 and held at 32 degrees C is shown to be impaired. CARNA 5 accumulation in tomato at 32 degrees C is reduced about 100-fold compared to accumulation in plants held at 24 degrees C, while viral RNA accumulation is reduced about 5-fold. CMV-infected tomato held for 3 days at 24 degrees C prior to shift to 32 degrees C do not develop lethal necrosis. Longer incubations at 24 degrees C prior to shift to 32 degrees C allow necrosis to develop. CMV-infected plants held for up to 4 weeks at 32 degrees C required an additional 8-10 days at 24 degrees C to develop necrosis. Necrogenic CMV-infected plants held at 24 degrees C and analyzed 3 days p.i. contained detectable amounts of ss- and ds-CARNA 5; upon shift to 32 degrees C, such CARNA 5 declined to undetectable levels and lethal necrosis did not occur. There appear to be temperature-sensitive factors that are required for efficient satellite replication which are not required for efficient viral RNA replication. Whether these factor(s) are of host or satellite origin is uncertain.

Cucumovirus↗
PubMed1995

Effect of temperature on cucumber mosaic virus satellite-induced lethal tomato necrosis is helper virus strain dependent.

The effect of temperature on the response of tomato (Lycopersicon esculentum Mill. cv. Rutgers) to infections with the necrogenic cucumber mosaic virus (CMV) satellite D-CARNA 5 was investigated with each of four CMV strains D, 1, Y and S functioning as helper virus. At 24 degrees C lethal necrosis was observed in all infections. However, at 32 degrees C the response varied from total absence or reduction of necrosis with some strains to accelerated lethal necrosis with others. The total lack of necrotic response with CMV-S and the aggravated necrosis with CMV-Y at the higher temperature both turned out to be independent of the coinfecting satellite, and rather to correlate with the changing rate of viral RNA accumulation in tomato, which probably was responsible for the changes in pathogenic response. However, when CMV-D was helper virus, satellite accumulation decreased, while with CMV-1 it increased, respectively, while viral RNA accumulations were not seriously affected. Although these profound effects of temperature seem to link the necrotic response of tomato to the competitive replication dynamics of the infecting virus/satellite combination in the case of CMV-D/D-CARNA 5, temperature effects at other levels of disease induction probably play an important role as well.

Cucumovirus↗
PubMedDate not supplied

Cucumber-mosaic-virus-associated RNA-5. XII. Symptom-modulating effect is codetermined by the helper virus satellite replication support function.

In tomato, the disease-modulating effects of a cucumber mosaic virus (CMV) satellite isolate from Belgium, here designated T-CARNA-5 (CARNA-5 = CMV-associated RNA-5), were found to be different depending on the supporting helper virus strain. With two CMV strains, T-CARNA-5 induced lethal necrosis, but with a third strain from Ixora spp. (CMV-Ix), aggravated stunting was observed. However, the primary structure of the T-CARNA-5 contained within virus isolated from tobacco or tomato infected with each of these three CMV strains, conformed to the conserved sequence profile of CARNA-5 isolates which are necrogenic in tomato. Dilution endpoint bioassay of T-CARNA-5 established a direct cause-effect relationship between it and tomato necrosis or stunting, depending on the helper virus. Total nucleic acid extracts taken at different times from tomato plants infected with the above CMV strains and T- or S-CARNA-5 (used as non-necrogenic control) showed viral RNA, ssCARNA-5 and dsCARNA-5 to be present in significant amounts, but in sometimes dissimilar proportions depending on the combination; except in CMV-Ix/S-CARNA-5 infection where neither ss-nor dsCARNA-5 was found. The experiments established that CARNA-5 biological expression studies in CMV-infected tomato have to take into account the helper virus satellite replication support function, which may be a primary codeterminant of quantitative or qualitative differences in the symptom modulation observed.

Base Sequence↗