Dit is een uitgebreide hoorcollege aantekening over oxygen sensing in plant development met figuren van de powerpoint, gegeven door Daan Weits. Alles wat aan bod is gekomen, staat in deze samenvatting. Er worden kopjes gebruikt zodat je weet waar het precies over gaat. Het is in het Engels geschrev...
Oxygen sensing in plant development
Learning goals:
- Understand important differences between plant and animal development
- Explain how plants and animals sense oxygen
- Outline the role of oxygen in plant physiology and development
- See examples of how molecular cell research is carried out in plants.
The study of plants is very important because most of our food comes from plant sources or
plant sources are used to feed animals that we eat.
The differences in growth and development in plants vs. animals
One major difference is that plants keep developing
throughout their lifetime. So they make new organs
throughout their life cycle (see figure).
Plants’ development is very variable, but also flexible.
Plants can change their development. For example, they
can make specialized leaves that trap insects for food but
they can also get somatic embryogenesis on leaves so they
make clones.
Another difference is that cell fate control. In animals, cell
fate is controlled by lineage but the cell fate in plants is
primarily controlled by the position of the cells.
If this is true, this means that we can re-program cell faith in plants using auxin or other
hormones. And this is true. So somatic
explants (leaves, roots, petals, etc.) can all
dedifferentiate into callus (undifferentiated
state). Plants have no germline and all their
cells are totipotent. And reprogramming can
be induced using just two hormones.
Plants are sessile, so they can’t move. So when they face adverse factors in their
environment, they should adjust their development and growth to the environment to deal
with this. So the plant development is highly responsive to the environment. When nitrogen is
removed in the soil, they develop a highly expanded rootsystem. Plants grow to the side
where the light is coming because they want to capture the light. They also respond to abiotic
stress (flooding), like they can change their leave shape.
The fifth difference is that you can
easily create transgenic plants. So
stable plant transformation is
convenient. Plants can be
transformed using agrobacterium
transfer DNA (T-DNA), giving many
transgenic collections (knockouts,
overexpressors, etc.).
Due to these different constraints/ advantages, it is best to study cellular responses in tissue
and organismal contexts instead of cells.
, Role of oxygen sensing in plant development and abiotic stress
One of the most common conditions in which plants face low oxygen (hypoxia) is flooding.
This is a problem because gas diffusion is very slow in water compared to air. This causes a
severe reduction in oxygen and CO2 levels, which leads to an energy crisis. This could be
reduced when the water is very clear, but the water is usually very cloudy so the water
turbidity is high, and this results in reduced photosynthetic activity.
Water excess is a relatively common stress condition that plants face, however, several wild
species and few crops rather thrive in such an environment. So how do plants sense low
oxygen and what can we learn from hypoxia-adapted species?
Plants cope with oxygen scarcity by employing
adaptive strategies (morphological strategies) or
anaerobic metabolism. Both of these strategies
are regulated by a transcription factor (ERFVII).
These control fermentation and some
morphological changes.
These ERFs are composed of multiple
members, such as constitutive and hypoxia-
inducible members. The constitutive members (RAPs) are always present and do not really
respond to hypoxia. The hypoxia-inducible members (HRE) expression increases during
hypoxia.
When making an overexpression of RAP2.12, the plants
confer submergence tolerance so they do better after being
flooded compared to the control group. But by adding a
TAG (to isolate the protein), they do worse after flooding.
This TAG was on the N-terminus, so they expected the N-
terminus to be important. By removing the first 13 amino
acids, they got the same effect. So the N-terminus is very
important.
But why? By looking at the conservation of amino acids at
the N-terminus, they found a very conserved sequence that
appears in every factor of ERFVII. So this conserved N-
terminus sequence has a very important degradation factor
of this transcription factor.
This was a big discovery, which revealed some
oxygen sensing on a molecular level. When there is
hypoxia, the ERFVII dissociates from the membrane
and is translocated to the nucleus. Here it will activate
genes important to the hypoxia response. However,
after re-oxygenation, these proteins are degraded. But
is this ERFVII degradation enzymatic?
ERFVII has a very conserved N-terminus, consisting of Met-Cys. Cysteine is very reactive
and when there is oxygen, the cysteine is oxidized. This is where the sensing takes place.
After oxidization, other factors and amino
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