Ubiquitin-Proteasome System-Mediated Protein Degradation in Defense Signaling - PAMP Signals in Plant Innate Immunity: Signal Perception and Transduction - page 420

then translocated into rice cells. AvrPiz-t suppressed the ubiquitin ligase activity of
the rice RING E3 ubiquitin ligase. Silencing of the ubiquitin ligase in transgenic
rice enhanced susceptibility of rice plants to M . oryzae , suggesting the role of the
ubiquitin ligase in disease resistance (Park et al. 2012 ). The results suggest that the
fungal pathogen causes the disease by suppressing the ubiquitin-proteasome.
DNA viruses selectively interfere with CUL1-based SCF ubiquitin E3 ligases to
cause infection in plants (Lozano-Durán and Bejarano 2011 ; Lozano-Durán et al.
2011 ). The DNA viruses redirect ubiquitination by interfering with the activity of
the COP9 signalosome (CSN) complex. The geminiviral C2 protein interacts with
CSN5 (COP9 signalosome5), and its expression in transgenic plants compromises
CSN activity on CUL1. Several responses regulated by the CUL1-based SCF ubiq-
uitin E3 ligases (including responses to jasmonates, auxins, gibberellins, ethylene,
and abscisic acid) are altered in these plants (Lozano-Durán et al. 2011 ).
Transcriptomic analysis of the transgenic plants showed that the response to jasmo-
nates is the main SCF-dependent process affected by geminiviral C2 protein.
Exogenous JA treatment of Arabidopsis plants disrupts geminivirus infection sug-
gesting that the suppression of the JA response might be crucial for infection. SCFs
are key regulators of JA signaling. The capability of viruses to selectively interfere
with or hijack the activity of these complexes may be a powerful strategy in viral
infection (Lozano-Durán et al. 2011 ).
Sahana et al. ( 2012 ) showed that a cell permeable proteasomal inhibitor facilitated
an increase in Papaya ringspot virus (PRSV) accumulation in the host papaya
plants. The PRSV viral protein HcPro was found to interact with the 1 subunit of the

20S proteasome, inhibiting the action of the 20S proteasome. The results suggest
that inhibition of the host proteasome facilitates the virus accumulation in the host
plant and the proteosomal catalytic activity is modulated by the viral protein.
Collectively, these studies suggest that proteasome is involved in virus disease resistance
and the potential viral pathogens inhibit the proteasome activity and induce the
disease incidence infection.

α

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