Mitochondria, plastids and DNA inheritance - replies

Jim Cummins cummins at possum.murdoch.edu.au
Mon Feb 14 23:47:55 EST 1994


In article <2jnajtINNq07 at newsman.csu.murdoch.edu.au>
cummins at possum.murdoch.edu.au (Jim Cummins) writes:

> Two questions
> (1) Is there any other evidence that plastids contain unique DNA?
> (2) Is there any other evidence of biparental inheritance of
> non-nuclear DNA?  I thought maternal inheritance was obligatory. 
> 
> PS (I'm sure not to be alone in this :^)) What is a plastid?
I've receives such a wonderful variety of responses that I thought it
best to post a compilation.  It's quite clear that there is a wide
variety of cytoplasmic inheritance patterns available.  The interesting
questions is why in so many systems biparental inheritance is
suppressed.  Matt Ridley, in his excellent book :The Red Queen. Sex and
the Evolution of Human Nature" (Viking Press) speculates that it may be
to avoid potentially destructive genome competition.  Thus in the
mammalian system ()the one I'm most familiar with) one can conceive of
it as part of a game plan in which the sperm "sacrifices" its mtDNA for
the greater benefit of having its nuclear DNA survive.  Interesting to
see if this sparks a new thread.   Anyway, here goes withthe
compilations:
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Jim;
    I published some time ago what I think is to date the only data
demonstrating biparental inheritance of mitochondria with specific
genotypes in rapeseed (Brassica napus): Mol Gen Genet (1990):222:135.
    The incidence of biparental inheritance of chloroplasts (plastids
give rise to chloroplasts, amyloplasts, chromoplasts ..) seems to be
more widespread, but perhaps that's because there are more
chloroplast markers available than mitochondrial markers in plants. I
was able to use cytoplasmic male sterility as a mt marker and
triazine resistance (herbicide) as a cp marker in my study.
    My question is: Why do we not see more incidence of biparental
inheritance? I believe that EM studies show that paternal mt are
transmitted to the egg cell but they do not replicate and the DNA
does not seem to replicate either. Could it be that there is some
form of genome imprinting on the paternal mt genome such that it
cannot replicate following meiosis or shortly thereafter?
    Someday I may go back to that area of research, but am currently
doing other things. If you have any ideas on this, I'd be happy to
hear them.




Larry R. Erickson,
Department of Crop Science,
University of Guelph,
Guelph, Ontario,
Canada  N1G 2W1
Internet: LERICKSO at CROP.UOGUELPH.CA
Fax: 519-763-8933  Phone: 519-824-4120 Ext. 3398
         ********************** REPLY: ***********************
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  A plastid is a subcellular organelle in plants which is bounded by a 
double membrane (like mitochondria), contains its own unique DNA, RNA, 
and ribosomes (like mitochondria), and is dependent on the nuclear 
genome for function (like mitochondria).  The best known example of a 
plastid is the chloroplast, which contains the machinery for 
photosynthesis (both light energy transduction and the so-called "dark 
reactions" photosynthesis which synthesize sugar from CO2 and H2O).  

The evidence that chloroplasts, like mitochondria, contain unique DNA 
is extensive and has been accumulating for decades.  Molecular 
evolutionists have even identified candidate blue-green (prokaryotic) 
algal species which may be descendants of primordial endosymbiotic 
precursors of chloroplasts, on the basis of similarity of plastid 
genomes with the blue-green algal genomes.

(name not given - from ebarak at nsf.gov)
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       A plastid is a term that encompasses chloroplasts, chromoplasts,
etioplasts, proplastids, and some others. These are organelles found in
plants and algae. For most intents and purposes one may think of these
different types of plastids as being different developmental states of
a
chloroplast. That is, if a seed germinates in darkness, the organelle
is an
etioplast, and only in the presence of light, with the etioplast
develop
into a chloroplast. Likewise, in a maturing fruit, a tomato say, while
the
fruit is green, it contains chloroplasts, but the transition to the red
color involves the chloroplasts developing into chromoplasts, ie, there
are
numerous specializations that occur in these organelles which change
their
function along with their color. 

        I assume that you know that chloroplasts contain their own
genomes. 

        As far as the inheritance of organellar genomes goes, it can be
anyway you like. There are plenty of examples of biparental ineritance.
I
think that it is more realistic to think in terms of a continuum, with
there being some percentage of organelles contributed by each type of
gamete. In many model genetic systems (mice, maize, drosophila, etc) it
happens that the percentage contributed by the male is essentially
zero.
But in many other systems, as the one cited above, the contribution may
reach 50%. 

        Hope this helps.
                        Tobias Baskin (a gasp PLANT cell biologist)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Tobias I. Baskin                           
Baskin at biosci.mbp.missouri.edu
University of Missouri * Division of Biological Sciences * 109 Tucker
Hall
Columbia, MO 65211 USA      voice: 314-882-0173          fax:
314-882-0123
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Jim:

This is the first i have heard of biparental inheritance of non nuclear
DNA.   I think its a good idea :=)   evolutionarily speaking even if it
only happens once in a while.

Chloroplasts are an example of plastids.  All plastids want to be
chloroplasts but if they are in the endosperm of a seed thay are
usually
"forced" to be amyloplasts.  They certainly do have their own DNA.

BTW no chloroplast or mitochondria is an island, they need the nucleus.
Allen

Thanks for sharing

(from adwright at iastate.edu)
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Plastid = chloroplast.  There are other kinds of plastids, e.g.
chromoplasts, which give color to things like tomatoes, but basically
they
are all chloroplast derivatives.

> (1) Is there any other evidence that plastids contain unique DNA?
This is quite well established.  The entire chloroplast DNA molecule
has
been sequenced for several plants - tobacco, rice, the colorless plant
Epifagus, a liverwort, Euglena.

Maternal inheritance of chloroplast DNA is the rule for most land
plants,
although there are exceptions (e.g. the Pelargonium mentioned in the
reference above), as is maternal inheritance of mitochondrial DNA in
mammals.  Once you get down among the algae, fungi, and other "lower"
critters, there are no hard and fast rules.

Elizabeth Harris
chlamy at acpub.duke.edu

Redwoods inherit mitochondria paternally, I am told, 
and why not?

    --bks
-- 
Bradley K. Sherman               P.O. Box 245                    
Computer Scientist               Berkeley, CA, 94701
Dendrome Project                 510-559-6437 FAX: 510-559-6440  
Institute of Forest Genetics     Internet: bks at s27w007.pswfs.gov
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Thanks to all who contributed! 

Jim Cummins                   
School of Veterinary Studies
Murdoch University
Western Australia 6150  Tel +61-9-360 2668 Fax +61-9-310 4144
"An inordinate fondness for Beetles"



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