Cryptochrome 2 and phototropin 2 regulate resistance protein-mediated viral defense by negatively regulating an E3 ubiquitin ligase

Abstract

Light harvested by plants is essential for the survival of most life forms. This light perception ability requires the activities of proteins termed photoreceptors. We report a function for photoreceptors in mediating resistance (R) protein-derived plant defense. The bluelight photoreceptors, cryptochrome (CRY) 2 and phototropin (PHOT) 2, are required for the stability of the R protein HRT, and thereby resistance to Turnip Crinkle virus (TCV). Exposure to darkness or blue-light induces degradation of CRY2, and in turn HRT, resulting in susceptibility. Overexpression of HRT can compensate for the absence of PHOT2 but not CRY2. HRT does not directly associate with either CRY2 or PHOT2 but does bind the CRY2-/PHOT2-interacting E3 ubiquitin ligase, COP1. Application of the proteasome inhibitor, MG132, prevents blue-light-dependent degradation of HRT, consequently these plants show resistance to TCV under blue-light. We propose that CRY2/PHOT2 negatively regulate the proteasomemediated degradation of HRT, likely via COP1, and blue-light relieves this repression resulting in HRT degradation.light | photoreceptors | plant defense | virus | resistance protein P lants are dependent on light for their survival. The light-absorbing ability of plants is derived from the activities of three known classes of photoreceptors. These include phytochromes (PHY) that detect light in the red/far-red (600-700 nm) range, and cryptochromes (CRY) and phototropins (PHOT) that detect light in the blue and UVA (320-500 nm) range (reviewed in refs. 1-6). Photon-absorption activates the PHY proteins from their physiologically inactive to active far-red absorbing forms. Light also modulates the phosphorylation and nucleocytoplasmic translocation of PHY proteins, which is essential for their function in mediating light-responsive physiological changes in plants. CRY photoreceptors are flavoproteins that share sequence similarity to DNA-repair enzymes called photolyases. However, CRY proteins have no DNA-repair activity (5, 7). CRY proteins were first characterized in Arabidopsis, but are also widely distributed in bacteria and eukaryotes. These proteins usually contain an amino terminal photolyase-related region and a carboxy domain of variable size. Both isoforms of CRY (CRY1 and CRY2) in Arabidopsis undergo blue-light-dependent phosphorylation (8, 9), and CRY2, but not CRY1, is degraded in response to blue light (10, 11). Both CRY1 and CRY2 interact with constitutively photomorphogenic 1 (COP1), an E3 ubiquitin ligase (12,13). It is thought that blue-light perception by CRY photoreceptors triggers the rapid inactivation of COP1 through their direct protein-protein interactions (12, 13), resulting in the abrogation of COP1-mediated degradation of the bZIP transcription factor HY5 and other COP1 substrates (14). Although CRY1 protein shuttles between the cytoplasm and nucleus, the CRY2 protein is mostly present in the nucleus (15). Because CRY2 also contributes to anion channel-mediated currents across the plasma membrane (16), it is possible ...

Antiviral Resistance Protein Tm-22 Functions on the Plasma Membrane

“…3), we conclude that Tm-2 2 is a peripheral PM-associated protein. These findings are consistent with previous reports that several PM-localized R proteins, such as Arabidopsis RPM1 and HRT, are shown to be peripherally associated with the PM (Boyes et al, 1998;Jeong et al, 2010), and RPS2 is an integral membrane protein (Axtell and Staskawicz, 2003).…”

The Extent to Which Methyl Salicylate Is Required for Signaling Systemic Acquired Resistance Is Dependent on Exposure to Light after Infection

“…Light and disease resistance also may be linked via cross-talk between photoreceptor signaling and components of the resistance pathway. Light-dependent resistance to Turnip crinkle virus was shown to require cryptochrome 2 and phototropin 2 (Jeong et al, 2010). By contrast, HR development and local resistance to infection by Pst avrRpt2 were found to be dependent on phytochromes A and B (Genoud et al, 2002).…”

Canopy Light and Plant Health

“…There is also evidence that cryptochrome1 (cry1) is a positive modulator of Arabidopsis defense against P. syringae pv tomato DC3000 when plants are exposed to continuous light after pathogen infection (Wu and Yang, 2010). However, other studies, carried out under day/night light cycles, failed to detect any effects of mutations in B photoreceptors on Arabidopsis resistance to this bacterial pathogen (Griebel and Zeier, 2008;Jeong et al, 2010). Moreover, cry1 mutants did not show any obvious susceptibility phenotype in bioassays with the necrotrophic fungus B. cinerea (Cerrudo et al, 2012).…”

“…Similarly, the role of blue light (B) and B photoreceptors in the regulation of defense responses is not well established. Jeong et al (2010) reported that cryptochrome 2 and phototropin 2 are specifically required for resistance protein-mediated Arabidopsis defense against Turnip crinkle virus. There is also evidence that cryptochrome1 (cry1) is a positive modulator of Arabidopsis defense against P. syringae pv tomato DC3000 when plants are exposed to continuous light after pathogen infection (Wu and Yang, 2010).…”