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I'm Professor Christopher Howe
from the Department
of Biochemistry
at the University of Cambridge
in the United Kingdom
I'm going to talk about
the chloroplast genome
and chloroplast gene expression.
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We'll look, first, at the
experiments that led to
the recognition that
the chloroplast has
its own genome and
genetic system.
We'll then look at
the organisation
and content of the
chloroplast genome.
We'll look at the expression
of the chloroplast genome.
Finally, we'll consider
why there should be
a separate genome in
the chloroplast at all.
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The first experimental
observations that ultimately
were interpreted as indicating
the presence of a
chloroplast genome,
were reported early in
the 20th Century in
two classic papers by Carl
Correns and Erwin Baur.
Those papers looked
at the inheritance of
variegation in plants
that included Mirabilis,
which is also known as
the 4:00 o'clock plant,
and Pelargonium, the geranium.
Although some instances
of variegation in plants
were found to be
inherited according
to classic Mendelian principles,
this wasn't always the case.
In these exceptions,
the results of a cross
were found to depend
on the maternal,
that's to say the female parent,
the parent that produced the
egg, and not the pollen.
This phenomenon was termed
a reciprocal cross effect.
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Correns showed with
variegated Mirabilis,
that when green shoots,
as the female parent,
were pollinated with pollen
from a white plant,
as the male parent,
the progeny were always green.
When the reciprocal
cross was performed,
then the results were different.
With the reciprocal cross,
when white shoots were
pollinated with pollen
from a green plant,
the resulting
progeny were white.
Now, with conventional
Mendelian inheritance,
the results of the cross
should be independent of
which parent is male
and which is female.
The pattern observed
with the maternal parent
alone determining the
outcome of the cross
was referred to as maternal,
or sometimes uniparental-maternal,
inheritance.
With Pelargonium, the results
were a bit more complicated,
with both parents in principle
able to contribute to
the results of a cross,
but again not according to
a recognised standard
Mendelian pattern.
In that case, it is referred
to as bi-parental inheritance.
These results have been
extended to a wide range
of other plant species and
we now recognise maternal,
bi-parental, and paternal
inheritance patterns.
We understand these
patterns as being
