Answers to Aspergillus sectoring

Roxanne A Yamashita roxanney at bcm.tmc.edu
Fri Dec 13 11:10:52 EST 1996


Date: Wed, 4 Dec 1996 14:32:22 -0800 (PST)
From: Judy Roger <judyr at hevanet.com>
To: Roxanne A Yamashita <roxanney at bcm.tmc.edu>
Subject: Re: Aspergillus sectoring on plates. Help!

Try Toby Feibelman:  her e-mail is: Toby at nola.SRRC.USDA.Gov
good luck!

Date: Wed, 4 Dec 1996 20:57:54 -0800
From: David Geiser <dgeiser at mendel.berkeley.edu>
To: Roxanne A Yamashita <roxanney at bcm.tmc.edu>
Subject: Re: Aspergillus sectoring on plates REPOST

In article <585hip$knu at gazette.bcm.tmc.edu>, you write:
>Hi! I have been looking at a few aspergillus mutants via their growth
>from a single inoculation point on plates.  I noticed that the mutants
>have a great deal of sectoring (5-10X the amount of the wt GR5).  I
>believe that some of this is due to the Aspergillus kicking out the
>integrated insert, but I would like some other ideas.

Sounds like a good guess to me.

  What is known
>about this phenomena on species in the wild?

Generally,  wild isolates of A. nidulans don't do much sectoring. 
But to understand what's going on,  there are a lot of things to
consider.  What other mutations does the mutant have?  Is it diploid?
What do the sectors look like (happy or unhappy compared to the
mutant parent)?  What is the mutation you're looking at?  What medium
are you using?  I assume that the transformation involved some sort
of selection - what was it?

Perhaps you can find one transformant that's stable and just deal
with that one.

Good luck, Dave Geiser


Date: Fri, 06 Dec 1996 10:26:29 +0000
From: "J. J. Steffens" <steffejj at a1.esvax.umc.dupont.com>
To: Roxanne A Yamashita <roxanney at bcm.tmc.edu>
Subject: Re: Aspergillus sectoring on plates REPOST

It is possible that stable integration has not occurred in your
isolates, or that your are dealing with heterocaryons.  If your
transforming plasmid contained the AMA locus, the transforming DNA is
maintained as a self-replicating plasmid which can be isolated  from
fungal DNA preps.  Using such plasmids, one can pick transformants
which do not contain integrated plasmid by their unstable phenotype.

Did you single spore your transformants following regeneration on
selective media?

Date: Tue, 10 Dec 1996 10:18:58 -0800
From: upshalla at zgi.com
To: roxanney at bcm.tmc.edu
Subject: Re: Aspergillus in the wild


Roxanne, your e mail made it to my screen, and I think I can partly 
answer your
questions.  However, while I believe the R153 strain is wA3, pyroA4 
(originally
from Clive Roberts in Leicester England)I do not know the genotype of the GR5
strain.  Perhaps you could enlighten me on that and its origins.  THe 
R153 is a
standard control strain not a wild type. Wild types have no induced 
mutations.
However, R153 has been tested in meiotic and mitotic analyses and shown 
to be
chromosomally normal (Upshall and Kafer 1974).  I do not know if there is any
deviation in chromosomal gel analysis.  This strain should not show any
abnormal
sectoring under normal growth conditions, so what media are you growing 
it on?
Are you seeing sectoring in the mutated strains only, or in both mutated and
parent.  Are the sectors the same phenotype or different between parent and
mutant?  Are the sectors more normal or more abnormal in phenotype?  
Sectoring 
can be the consequence of abnormal chromosome segregation to,yield 
aneuploids,
or after mutagenesis, chromosomal rearrangements which are resolving to
stability, or duplications to provide gene dosage compensation for a 
deficient
function.
I'm sorry this might be vague but if you can provide me with more information
and description I will try to help.
Say hello to Greg May for me please, he'll appreciate this voice from the 
past.
regards
alan upshall


Date: Thu, 12 Dec 1996 18:56:59 -0800
From: martat at pw.usda.gov
To: roxanney at bcm.tmc.edu
Subject: Aspergillus

Hi, Roxanne,
Certainly sounds like sectoring is some kind of gene expression phenomenon.
My guess would be that in a wild type strain (lacking an introduced
insert), while there could be rearrangements, you are more likely looking
at changes in gene expression. The altered expression could be of almost
any gene affecting growth or morphology. Here I'm thinking of a paper on
Neurospora by Mishra (Adv. Genet. 19:341), which reports different colony
morphologies depending on mutation present; but some of these patterns are
shown by wild type depending on growth medium.
Also the phenomenon you describe is reminiscent of some plant phenomena.
The most obvious one is in maize (patches of different colors in kernels)
and is due to the presence of inherent or introduced transposable elements.
Another phenomenon is a change in morphology during tissue culture of some
portions of the tissue; in part this is due to spontaneous mutation and
genetic rearrangements, apparently triggered by the culturing process.
Another phenomenon which may be related is observed in flax plants, where
depending on the growth conditions (nitrogen levels, for example), some
varieties change morphology, and the change is heritable. The change in
morphology correlates with differences in rRNA levels. Unfortunately I
don't have ready access to these papers, but the author's name is (Chris?)
Cullis, and they were published in the 1980's. (If you think they'd be of
help, and can't locate them, let me know and I can try to dig them out.)
As to what's causing the sectoring, ??? Could be something inherent to
culturing, or could be local differences in nutrient levels that trigger
such events. Maybe you've even got transposons. Sounds like a very
interesting biological question. If you can get enough material, it should
be possible to test for transposons, or for transcripts whose abundance
changes. Best of luck!
--Marta






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