Ubiquitin-Proteasome System-Mediated Protein Degradation in Defense Signaling - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 406

Chapter 10
Ubiquitin-Proteasome System-Mediated
Protein Degradation in Defense Signaling

Abstract Ubiquitin-proteasome system plays important role in the complex PAMP
signal transduction systems involved in plant innate immunity. JAZ proteins, which
are activated by jasmonate (JA) signals, act as repressors of JA-dependent transcription
factors. COI1 protein, a receptor of JA signal, forms a functional E3 ubiquitin ligase
and is required for removal of repressors of the JA signaling pathway. Ubiquitin
proteins-cullin-RING ligases negatively regulate biosynthesis of ethylene. Ethylene
signal transduction terminates in a transcription cascade involving the EIN3/EIL
and ERF families of transcription factors and ubiquitin ligases regulate the stability
and expression of these transcription factors. Ubiquitin proteasome may positively
or negatively regulate SA biosynthesis. A 26S proteosome is involved in triggering
SA accumulation, probably by removing/degrading an inhibitor of SA biosynthesis.
Ubiquitin ligases are also involved in regulation of R proteins-mediated defense
responses. Major function of ubiquitin ligases may be in conferring stability to
R proteins, probably by degrading the proteins involved in reducing the stability
of R proteins. Small ubiquitin-like modifi er (SUMO) plays a signifi cant role in
SA-mediated systemic acquired resistance. Ubiquitin-proteasome is involved in
triggering defense responses and virulent pathogens may subvert ubiquitin-proteasome
system to cause disease.

Keywords JAZ proteins • COI1 protein • Ubiquitin ligases • 26S proteasome • SUMO

10.1 Ubiquitin-Proteasome System in Plants

Ubiquitin- and proteasome-mediated degradation of proteins plays an important
role in plant defense signaling system (Dreher and Callis 2007 ; van den Burg et al.
2008 ; Trujillo et al. 2008 ; Sahana et al. 2012 ; Yao and Ndoja 2012 ; Yao et al. 2012 ;
Zhang et al. 2012 ). More than 1,300 genes identifi ed in the Arabidopsis thaliana
genome have been shown to be involved in the ubiquitin-proteasome pathway,