I'm Professor Hillel Fromm, Head of
the department of molecular biology and
ecology of plants at Tel Aviv University.
Today I will talk about calcium
regulation of transcription in plants.
First, I will give
an overview of the origin and
status of calcium in plant cells.
And I will specifically address
the relationship between the calcium in
the cytosol and in the nucleus.
I will then describe mechanisms by which
calcium regulates gene expression.
And I will further on give examples of
how calcium regulated transcription
is involved in plant defenses,
in biotic and abiotic stresses.
And how calcium regulation of
transcription is involved in hormonal
function and plant growth.
One of the intriguing properties of
calcium in plant cells is that calcium is
involved with any interaction
of plants with the environment.
This includes the biotic and
It includes responses to physical
stimuli like light, heat, cold,
mechanical stress and to chemical stimuli
like salinity, drought and hypoxia.
The important role of calcium in cellular
life and in plants cells specifically,
that we probably traced back
to early evolution of cell.
Due to the properties of calcium,
it's fast binding to proteins and
It's strong binding, high availability,
and limited solubility.
Early cellular life required ejection
of calcium from the cells to create
a situation where the concentrations
of calcium in the cell is very low.
And thus creating a gradient of four
orders of magnitude of calcium from
outside to inside.
This was probably the initial step to the
evolution of calcium as a signaling system
When we look at the typical plant cells,
we see that the concentration of calcium
in the cytosol it is between
100 to 200 nanomolar.
The outside concentration of calcium in
Apoplast is between one to ten millimolar.
Calcium has the machinery to pump
out calcium from within the cell or
release calcium on the outside of from
an intracellular storage compartments.
And this compartment include chloroplasts,
mitochondria, the And
most importantly in plants the vacuole
which contains concentrations of calcium
to the ten millimolar range.
Upon perception of signals
from the environment,
calcium will be released into
the cytosol either from the outside or
from intracellular compartments, and
will create a calcium signature.
So for each stimulus from the outside will
be a different pattern of calcium that is
called a calcium signature.
The question now is how genes
are regulated by calcium.
Since the genes are in the nucleus,
we have to ask the questions of what
happens with calcium in the nucleus.
The nucleus is not a sealed envelope but
actually contains pores that can even
let proteins go into the nucleus.
So for many years it was assumed that
calcium simply moves freely through these
pores into the nucleus.
However, now it's believed that calcium
cannot move freely through these pores.
It may go through these pores
under certain circumstances.
However the most interesting thing is
that the nucleus has calcium storage and
release machinery in the nuclear envelope.