University a
~~" College of Agriculture

of Kentucky

 

Oo PLANT PATHOLOGY
8-305 Agricultural Science Building — North

Lexington, Kentucky 40546-0091

(606) 257-2682

Fax: (606) 323-1961

March 25, 1996
Dear Professor Lederberg:

4
Thank you for your letter of March, 1996. I sent you an e-mail
message this morning. I enclose a set of reprints and a copy of the e-
mail message:

The project on fungal viruses has been my “pet” project for
sometime now. We have recently made considerable progress in the
molecular characterization of the viruses and we are applying
molecular approaches to address the interesting biological features of
this fungal-virus system

I'll respond to the points you raised in your letter in the following:

Transmission experiments using virus-free fungal protoplasts and
purified virions proved to be very inefficient, as I discuss in the
enclosed reprints of our work on transmission of the mycoviruses
infecting the plant pathogenic fungus “Helminthosporium victoriae”.
The transmission work was published in book chapters that are
based on “Symposia Proceedings”. I didn’t publish these studies as
Journal articles because I wanted first to optimize the conditions of
the infectivity assays. This proved to be time-consuming.

We have recently completed the molecular characterization of the
viruses involved and the virus system is very similar to the yeast
killer system (A helper virus that belongs to the family Totiviridae
and associated satellite dsRNAs). We have constructed full length
cDNA clones of the viral and satellite dsRNAs associated with
diseased isolates of the fungus. With the availability in our
laboratory of full length cDNA clones and of efficient DNA-mediated
transformation system for H. victoriae, we have resorted to
molecular biology techniques in order to study the etiology of the
disease phenotype. Using such a molecular approach, it has been

 

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unequivocally established that viral dsRNA is the causal agent of
hypovirulence in the chestnut blight fungus

My thoughts pertaining mechanisms involved in “segregation”
during protoplast formation and generation are as _ follows:
protoplasts originating from apical cells in young hyphae may be
virus-free or in case of double infections may contain only one of the
viruses. The practice of hyphal-tip subculture has been used in
curing virus-infected fungal cultures.

Examples of “cure” as a result of chemical treatment:
Cycloheximide has the most commonly used chemical for curing
virus-infected fungal cultures. Cycloheximide is known to inhibit
virus dsRNA synthesis selectively in fungal hosts.

References:

Fink, G. R. and Styles, C. A. 1972. PNAS 69, 2846-2849
Sweeney et al. 1976. Genetics 84, 27-42.

Lemke et al. 1973. J. Gen. Microbiol. 76, 285

Fulbright, D. W. 1984. Phytopathology 74, 722-724.

We are preparing a paper on the molecular characterization of the
190S virus of Helminthosporium victoriae and I will be glad to send
you a pre-print if you so desire.

I have recently wrote a rather lengthy review article on recent
developments in fungal virology (unfortunately I am out of reprints):

Ghabrial, S. A. 1994. New developments in fungal virology. Adv. Virus Res.
43:303-388.

With best regards.

Sincerely yours,

sl Prt d

Said A. Ghabrial