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NPR1 as Salicylic Acid Receptor
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NPR1: A Salicylic Acid Receptor
The NPR1 Protein
Salicylic acid is a plant defense hormone
which induces hypersensitive response and both local and systemic acquired resistance
C-terminal transactivation domain and nuclear localization signal
N-terminal BTB/POZ domain
The Arabidopsis NPR1 Protein Is a Receptor For the Plant Defense Hormone Salicylic Acid
Derk te Winkel
The immune system of plants 2012
Transcriptional coregulator NPR1 is central to the activation of SA-dependent defense genes
Discussion
Interaction between NPR1
and SA
Proposed model
Equilibrium dialyis
One binding site
Why NPR1 fits in the model as a receptor for SA
-NPR1 is saturable by SA, has a low Kd and is chemically specific.
-NPR1 is clearly accepted as the key regulator of SAR deployment and PR-1 activation.
-NPR1 mutations abolish SA-signalling leading to SAR and PR1 activation.
-active structural analogs directly bind NPR1, inactive analogs do not.
-Cys 521/529 are required for in vitro binding of SA, while in vivo mutation of these cysteines abolishes PR-1 activation by SA.
-SA disrupts the interaction between the BTB/POZ domain and the transactivation domain NPR1, in vivo and in vitro
Active and inactive structural analogs
How does NPR1 bind SA?
BTB/POZ represses the transactivation activity of Δ513 in the abcense of SA, but not as an autonomously acting repressor
Is NPR1 binding metal? Immobilized metal-affinity column
Is this metal binding important for binding SA?
In vivo coexpression of Δ513:DB with BTB/POZ
BTB/POZ doesn't repress already activated reportergenes
Question?
So far
Δ513 can activate transcription in
the absence of SA, full length cannot. Interaction between BTB/POZ and Δ513?
The results so far support a model in which SA binds to NPR1 via Cys 521/529 through the coordination of SA by a transition metal
Plant two hybrid assay
Plant transcription assay
BTB/POZ binds Δ513
Δ513 doesn't bind the column
An unrelated protein doesn't
bind BTB/POZ
What happens after NPR1 binds SA?
Gel filtration