Edinburgh, Scotland, United Kingdom - TAIR

Post-translational modifications of the transcription
co-activator NPR1 regulate plant
immunity
Systemic acquired resistance (SAR) is a plant immune response effective
against a broad-spectrum of pathogens. Activation of SAR is associated with
dramatic transcription reprogramming of over 2,200 genes to prioritize defense
responses over normal cellular functions. The transcription co-activator NPR1
directly or indirectly controls the expression of most of these genes. In the
cytoplasm of resting cells, NPR1 forms an oligomer through redox-sensitive
intermolecular disulfide bonds. Upon induction of SAR, changes in cellular redox
result in the release of NPR1 monomers, which translocate to the nucleus and
modulate gene transcription. To gain a better understanding of transcriptional
regulation in SAR, we investigated pathogen-induced changes in the equilibrium
between NPR1 oligomer/monomer conformations and studied the behavior of
NPR1 in the nucleus. We found that distinct post-translational modifications of
NPR1 control its activity. In the cytoplasm, S-nitrosylation of NPR1, a process in
which nitric oxide is covalently attached to a cysteine thiol, promotes oligomer
formation, while thioredoxins (TRX) facilitate the opposite oligomer-to-monomer
reaction. Moreover, in the nucleus NPR1 activity is regulated by cycles of sitespecific
phosphorylation coupled to ubiquitin-mediated degradation by the
proteasome. Degradation not only restricted the activity of NPR1 in the absence
of pathogen threat, it surprisingly also played a critical role in promoting coactivator
activity upon induction of SAR. The intimate interplay between different
post-translational modifications and their dynamic effects on NPR1 activity will
be fundamental to our discussion of regulatory mechanisms that govern plant
immune responses.
78
C27
Thursday 15:15 - 15:30
Plant Defence
Steven Spoel1
Yasuomi Tada2
Zhonglin Mou3
Natalie Spivey4
Xinnian Dong4
1Biology Department
Duke University
USA
(Present address: Institute
for Molecular Plant Science
University of Edinburgh
UK)
2Biology Department
Duke University
USA
(Present address:
Life Science Research
Center
Kagawa University
Japan)
3Department of
Microbiology and Cell
Science
University of Florida
USA
4Biology Department
Duke University
USA