One of my main research questions is to understand
how photosynthesis evolved in land plants and green algae. And this study provides really interesting clues as to how that process happened.
Photosynthesis in land plants and green algae arose more than
one billion years ago.
Plants and green algae
can perform photosynthesis
because they contain these specialized structures called chloroplasts
where light energy is converted to
chemical energy. Even though this is a
permanent fixture within plants and algae it once used to be free-living cyanobacteria.
A bacteria that can perform
photosynthesis.
Presumably these cyanobacteria were engulfed as food
but somehow they
figured out a way to
escape the digestion and
eventually evolved into the specialized
structure called the chloroplast. Without this event,
land plants and green algae wouldn't exist.
Without the evolution of all of those organisms,
there may have not been enough oxygen required for the origin and
diversification of animals.
This idea of bacteria-eating behavior
has been suspected. However because much of the land plants and green algae
do not have this feeding
capacity anymore, we had little idea as to how they acquired the predecessor
of chloroplasts in the first place. Cymbomonas is an early branching green algae
which means that it
may not have changed that much since it evolved. Previous studies
suggested that these
algae
may still retain the capacity for eating
bacteria. However
finding the definitive microscopic evidence
for this behavior
has been difficult because their
bacteria eating behavior
may be used only under particular growth conditions. So, this algae
can acquire food either by photosynthesis or by chasing after
bacterial cells. In our study we show that when there's enough light
they seem to prefer acquiring food only through photosynthesis.
When light was limited and photosynthesis became difficult
we saw
bacteria-feeding behavior. Even before this study people knew that some green algae have these
prominent vacuole, as well as narrow channel. However, it
was not really clear what they were used for.
In this study we showed clear microscopic evidence for it and then
further characterized what structures are involved in
bacteria feeding.
Prey bacterial cells
are drawn into these
mouth-like openings and they are transported through the narrow channel and
accumulate
in the large vacuole where the digest happens.
This research provides clues as to how the
ancestor to land plants and green algae acquired
the predecessor of the chloroplast. Now we want to investigate this feeding behavior
at the genetic and molecular sequence level. What genes are involved in this
bacteria-feeding behavior?
We also want to explore whether
other green algal species also
retained this capacity to feed on bacteria, using microscopic techniques.