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Plantdevelopment and environment colleges DT2
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A complete summary of the lectures of the second part in English (with pictures for pathways etc)
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Plant development and EnvironmentLectures Part 2
Shade avoidance, PIFs & Interactors
● Understand how PIFs and their activity are regulated
● Explain what types of PIF interactors exist
● Describe how PIF interactores co-regulate PIF activit
● Explain the BAP/D module
PIF (phytochrome interacting factors)
proteins control for shade avoidance.
Prf are active, they move to the nucleus,
interact with PIF and thats why PIFs can’t do
their work: activate shade induced genes. Now
they bind to Pfr and than the 26S proteasome
breaks them off.
PIFs have an APB domain: a domain where Pfr
can bind (phyBPfr).
PIF1 and PIF3 have an APA domain: a domain
where phytochrome A can bind (phyAPfr).
Phytochrome a is an antagonist of b.
PIF5 accumulates in low R:FR. PIFs accumulate in
dark -> and are degraded in light.
PIFs are phosphoproteins, and thus can be
phosphorylated and dephosphorylated.
PIF7 is more stable than PIF5 (gets slower
degraded in light), and it gets de-phosphorylated in
low R:FR.
PIFs bind E and G boxes on promoters.
The Gboxes are defined more specifically than the Eboxes.
PIFs interact with DELLA. This interaction controls the PIF
activity. GA binds to the GA-receptors, they inactivate DELLAs.
So by adding GA you can degrade the DELLA proteins and
therefore get rid of the inhibitory role that DELLA has on the PIFs.
DELLAs inhibit PIFs binding to the DNAs. There are multiple other
interactions with PIFs, not only DELLAs. For example: HY5
inhibits PIFs as well.
HFR1 is a PIF-induced inhibitor of the shade avoidance. It’s a
negative regulator of farred- responses. It binds to PIF via a helix-loop-helix-domain. It
,inhibits its binding to Gboxes.
Not all PIF-interactors inhibit their function. The
ARF and BZR interact and positively regulate their
function. It stimulates the hypocotyl elongation.
BZR promotes the brassinosteroids. ARF
promotes the auxin. All three of them stimulate
each other as well.
The whole set is called the BAP/D module.
Tweaking Shade
Avoidance
● Explain how plants distinguish future from
actual shade
● Understand hor R:FR signaling route is
modulated by cryptochromes
● Comprehend how shade avoidance magnitude can be modulated
● Understand how BAP/D module is targeted by environmental factors
● Explain how shade avoidance can be prevented
Leaf angles respond very early.
In a canopy: not only the R/FR ratio is changing but also the blue light. They can combine
these changes to know in what kind of environment they exist.
The R/FR ratio changes already when there are neighboring plants -> Early warning
signal. The blue light changes when the plant already is in the shade > late warning signal.
PIF4 and PIF5 regulate low light responses. The cryptochromes detect the light, and they
use it as well to tune their circadian clock.
PAR ( -> Total light intensity) is sensed through blue light.
PIF7 is needed for the low R/FR signal. The PIF7 does something in blue light, but not that
important as PIF4 and 5.
The cryptochrome phenotype is dependent on the PIFs.
, PIF5 accumulates in low blue (LB). It takes longer to accumulate PIF5 in LB than PIF7 does
in low R/FR. It is a slower response.
Low Blue and Low R/FR enhance petiole elongation to the maximum effect through the
auxin pathway.
It's not just auin, it’s also brassinosteroids. Together they bring up a really strong elongation
(alone as well, but not as high).
BAP/D: Far red is mostly the auxin pathway.
When there is low blue the brassinosteroids
pathway comes in as well.
ATHB2 and IAA19 are the most common marker
genes for shade avoidance. The’ll be upregulated
in low R/FR, and even more so in the combi
(LB+LR/FR).
HFR1 is also a shade avoidance gene. But this
one is less upregulated in the combi then in only
low R/FR. -> It’s slightly repressed. It’s normally a suppressor of shade avoidance. -> This
enhances the response!
It’s not only true for HFR1. It's true for multiple negative
SAS regulators.
Low Blue suppresses the suppressor.
- HY5
- HYH
PIF4, 5 & 7 & HFR1 control the canopy response.
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