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The mitochondria of all living systems contain their own genome, which codes
for proteins and RNA molecules necessary for cellular respiration. Some of
these proteins and RNA molecules, however, are functional only if they are
part of protein complexes. Other components of such complexes are encoded by
the nuclear genome. Therefore, coordination between the nucleus and
mitochondrion is important in protein expression and cellular respiration ?
the extent of that coordination, however, has been relatively unknown,Mai
2005.

Philippe Giegé, of the Institut de Biologie Moléculaire des Plantes in
France, and colleagues explore the ?Coordination of Nuclear and
Mitochondrial Genome Expression during Mitochondrial Biogenesis in
Arabidopsis.? Their findings appear in the latest issue of the Plant Cell
Online.

Using Arabidopsis plants as their model, researchers grew their cells in a
low sucrose cell culture system in order to modulate mitochondrial
biogenesis in response to sugar starvation. This system would also allow
them to see the extent of coordination of gene expression between
mitochondrial and nuclear genes during times of plant stress.

Using dyes to track mitochondria, as well as SDS-PAGE, DNA micro-arrays, and
protein blot systems to monitor protein expression, researchers found that
there was no coordination of expression of the two genomes at the transcript
level, and instead found that coordination could occur at the level of
protein-complex assembly. They also found that even with plant cells under
stress, mitochondria still continued to churn out their protein subunits,
while the nucleus had already stopped doing so in order to respond to stress
signals. This suggests that the mitochondrial genome, at least in this case,
could not perceive stress, and could still continue expressing it proteins
as though the cell were living normally ? thus leading to an excess of
unassembled mitochondrially-encoded (but eventually, non-functional)
proteins.

Download the complete article at
[www.plantcell.org].

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