Our final speaker for today is Professor John Bowman.
He joins us from the School of Biological Sciences
After obtaining a Bachelor of Science in biochemistry from the University
Illinois Professor John Bowman trained as a geneticist
during his PhD at Caltech where he started working on the Arabidopsis
as a model plant to address fundamental questions in plant development.
During his PhD and subsequent post-doc at Monash
he contributed substantially to our understanding of the development
of genetics of flowers. In 1995 he established his own laboratory at the
University of California in Davis
where his group discovered several gene families whose actions determined the polar growth
of leaves. During his time at Davis, John was named the Chancellor's Fellow
and received Beckham Young Investigator award.
In 2006, John moved as a Federation Fellow to Monash, where his laboratory continues to
investigate fundamental questions
in land-plant developments with an evolutionary perspective.
This year John was elected a Fellow at the Australian Academy of Sciences.
In his spare time John is a guide at the Fairy Penguin Colony at the St Kilder break water
and he also studies the colony with Earth Care St Kilda to work out how these
birds coexist
within a city of 4 million people. Today John is going to talk
on Evolution in the Cycles of Life. Thanks John.
Thanks Kaye, and thanks for the
opportunity to continue a sort of theme of evolution, maybe slowly getting closer to us.
I'll tell you a little story that actually all the work was done here at Monash
well under the auspices of the fellowship that I got which
and I'll say that I probably could have been done under a single grant cycle
So that's an argument for long-term funding for science.
So we look at life on Earth,
multicellularity, like our bodies,
evolved multiple times independently so we're over here
multicellularity evolved independently
and fungi which were quite closely related to in the big scheme of life
in brown algae which is completely different more often times people think
about brown algae as plants but they're not really plants they're actually more
closely related to the
malarial parasite than they are to plants and then
these groups are traditionally what we think of as plants where we have some
red algae
and a couple different lineages have green algae and these are land plants
and multicellularity evolve multiple times independently in all of these lineages
and my lab primarily works on these land plants
but if we think about where we all came from
was probably a single cell and the life cycle
of our common ancestor between us and brown algae in
plants had a life cycle to
was most likely similar to that found in a lot of single-celled organism still
alive today.
So this is a Chlamydomonas, a green algae.
They exist as single cells. This is a marine algae. And when nutrients are
getting low they decide, "maybe we should mate"
and they differentiate into different types of gametes called minus and plus
you can think about that in terms of us as being sperm and eggs
and then these two gametes fuse and then
they have a diploid phase. So there's single set of chromosomes in here called haploid
and in here there is diploid. After fertilisation, or fusion,
this diploid cell will undergo a process called meiosis which produces
four haploid organisms again.
So this is the simplest life cycle maybe you to go back to your first year
biology
now this life cycle can be modified to be multicellular in several
different ways
So in us what's happened is that in this diploid phase here
undergoes something that's called mitosis which is just cell divisions
producing
more identical cells, and each of them
have two copies of the chromosomes. In us
in the males, and the females, only a small subset of our
cells in our body undergo this process called meiosis
and a course that produces eggs in the female, and sperm
in the male, and these are single cells. They get together
to fertilization-same thing here-to produce
another diploid organism and then that grows up.
now but this isn't the only way multicellularity is evolved.
In some green algae fresh water green algae
instead of the diploid phase becoming multicellular,
the haploid phase evolved to become multicellular to begin with.
So then you have a multicellular complex haploid phase
of only which a certain small number of cells will differentiate
either is multi-sperm or as
actually in this case an enclosed egg. The sperm fertilizes the egg
forming this diploid cell which basically just undergoes meiosis to
produce more
haploid a organisms a swim around
Actually, in the early days in the 1800s, when they first started seeing
plants producing multicells, they called them
"animal-cules" or plant animals, because
plants weren't supposed to swim around but they're there quite common and
in most lineages of plants.
some organisms have evolved multicellularity in both generations
and the way this has happened at least in the case of land plants is it probably
evolved from an ancestor like this
that have this complex multicellular haploid phase
and then this diploid phase also has
evolved to become multicellular. So this complex multicellular produces
large body
of which are a subset of cells undergo meiosis to produce more haploid
organisms which grow into multicellular things which then produce
sperm and eggs to cope with the life cycle so
if Moss is a typical plant that
is like this and so if you're walking in the bush you can think about this when
you see the moss
these little green leafy things those are the haploid phase of the life cycle
in other words that's like our
eggs or sperm. Whereas the brown
sporocarp, called the "Fruiting Body",
is actually the diploid - so that's like the major part of our body.
So another way of thinking about complex life cycles like this
if we had this life cycle it would mean that we would produce sperm and eggs
but the sperm would develop into some multicellular being
and the eggs would develop into some multivellular being
and they'd go out to the pub and meet and mate
and our diploid bodies may not even know about it - so they're completely separate
So we're interested in understanding how these life cycles are regulated
and some of the insight came from Ursula Goodenough from Washington U
who's working on this organism Chlamydomonas, and they found
that the minus gametes produces a protein
cold Knox and the plus gamete produces a protein called Bell.
and these proteins are transcription factors
in other words there proteins that regulate the expert gene expression of other genes.
But the Knox protein in the Bell protein can't work on their own
rather they need to heterodimerise in order to bind to the DNA to activate
gene expression.
and so you can think about these gametes has been preloaded
with proteins that only after the fusion with the gametes are those proteins
a able to heterodimerise and then activate gene expression
to try to preload your gametes so good as soon as it meets a partner
it can start developing diploid phase of the life cycle.
so it turns out that in Chlamydomonas the Knox and the Bell basically
activate
genes that are expressed only in this diploid phase which eventually lead to
meiosis
In land plants it becomes a little more complicated but they also have Knox and
Bell
genes and one of the major events
leading to land plants was a duplication so now they have two differnet types
of Knox protein - we'll just call it Knox1 and Knox2.
and we believe that these are actually preloaded into the egg cell
to can think about the egg cell being the same as the minus can meet here
at the bill proteins are preloaded into
sperm she can't think about that being the same as the plus can meet here
and then when the sperm fertilizes the egg the
these different heterodimer dime Eric partners can
form Knox one with a bow or not to with the bow and they can activate
or repress gene expression in the deployed face
Sol I'll tell you a little bit oem data
that we had a on the Knox two genes in Los
and it turns out that as well
with me when I produced present in the last line is based on this data that
the Knox who is actually expressed in the Excel consistent with it being
preloaded into the game eat
but it's not expressed anywhere else in the haploid phase of the life cycle
however it is expressed this blue staining as gene expression is is
expressed throughout
indifferent a cells and tissues are the deployed phase of the life cycle
now in this particular Moss we can go in and we can
eliminate jeans by homologous recombination which means we just delete
the judge
new piece of DNA encoding a gene and so
when okay Kosaka could borrow who was a postdoc in the lab did this
she women aidid 22 Knox to jeans here and it turned out that rather than
getting these nice little brown
deployed fruiting bodies to the
to mutant didn't have never made them however when she extracted the mutant
she saw that they died when their about this stage in the
often produced these little funny outgrowths here and
so she took those mutant and wild-type embryos at that stage
and if you take a wild-type embryo and just place it on a are
a petri dish with some nutrient it'll just sit there
however if you took the mutant one and did the same thing
after about a week you should have got some filamentous
growth here and after a couple weeks this
looks pretty much like a wild type up wat phase
however this came from diploid cells here
so this is it when when you look at the number above
love chromosomes in here it's definitely a deployed organism
and so one hypothesis about what this gene dawes
is that win
fertilization occurs in new forms I go to new one and for the deployed phase
in organisms that have complex development and the haploid phase
you wanna make sure that this program never gets activated
in this phase so one you have to action activate the deployed genetic program
but you also need to repress the haploid genetic program
and so one roll of the Notch two genes Indian
Moss at least as to repress the haploid program during the deployed phase of the
life cycle
been you can use a human analogy and in this case it would be as if our bodies
all the sudden
d differentiated into a massive eggs and sperm
rights shifting from the deployed phase to the haps white face
so in because I who
quite limited time the
do function to the mock Swan we think is actually
to activity cell division and promotes the
building up the deployed body and the Knox to was to repress
the haploid body in there and 10 the one of our ideas right now was that
one of these evolved from the other one and we think that the
then the one we think the axe to repress gene expression evolved from the
activator
and we think that this is probably a very common theme in evolution of
transcription factors
do you have a transcription factor that does something the easiest thing to do
was appalled one
to rip it does the opposite thing right can still bind the same
a DNA sequence but interacts with different partners
and we think that this gene duplication producing these two
was really instrumental in the invasion or
above land by plants in general and and the reason why we think that is that
we need to build a complex multi so you were deployed bloody
in order to be efficient to reproduce on land
because if you if you don't think about flowering plants with Paul one
all the first land plants required aquatic fertilization they had more tile
sperm that would swim around
and now they're on land you can only be rely on having a caught a cab
environment to create new progeny a few times during the year through heavy do
are flooding or whatever
and if each fertilization event only gave rise to four progeny
my cat did back and knees than each
fertilization would only be a little bit of progeny and
whereas if you made a complex
multi-site were deployed you can get a thousand cells are 10,000 cells old
undergo meiosis and all the sudden
one fertilization or that would give you up you not not tens to hundreds of
thousands of progeny
and that would enable the the plants to colonize the land
even when they couldn't undergo their sexual cycle all the time
soul stop there because it's a nader's might be russ was out there
in