The E3 ubiquitin ligase COP1 (Constitutive Photomorphogenesis 1) is a well known component of the light-mediated plant development that acts as a repressor of photomorphogenesis. Here we show that COP1 positively regulates defense against turnip crinkle virus (TCV) and avrRPM1 bacteria by contributing to stability of resistance (R) protein HRT and RPM1, respectively. HRT and RPM1 levels and thereby pathogen resistance is significantly reduced in the cop1 mutant background. Notably, the levels of at least two double-stranded RNA binding (DRB) proteins DRB1 and DRB4 are reduced in the cop1 mutant background suggesting that COP1 affects HRT stability via its effect on the DRB proteins. Indeed, a mutation in either drb1 or drb4 resulted in degradation of HRT. In contrast to COP1, a multi-subunit E3 ligase encoded by anaphase-promoting complex (APC) 10 negatively regulates DRB4 and TCV resistance but had no effect on DRB1 levels. We propose that COP1-mediated positive regulation of HRT is dependent on a balance between COP1 and negative regulators that target DRB1 and DRB4.

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Published in PLOS Pathogens, v. 14, no, 3, e1006894, p. 1-23.

This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.

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This work was supported by grants 0641576 and 0749731 from the National Science Foundation to PK. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Related Content

All relevant data are within the paper and its Supporting Information files.

journal.ppat.1006894.s001.tif (539 kB)
S1 Fig.

journal.ppat.1006894.s002.tif (3121 kB)
S2 Fig. DRB proteins are required for HRT-mediated resistance.

journal.ppat.1006894.s003.tif (2765 kB)
S3 Fig. HRT interacts with DRB1, DRB3 and DRB5 but not DRB2.

journal.ppat.1006894.s004.tif (439 kB)
S4 Fig. The drb mutants show wild-type-like photomorphogenesis.

journal.ppat.1006894.s005.tif (1847 kB)
S5 Fig. DRB proteins interact with CP and DRB1 relocalizes to cytosol when coexpressed with CP.

journal.ppat.1006894.s006.tif (1796 kB)
S6 Fig. The APC overexpressing plants show normal photomorphogenesis.

journal.ppat.1006894.s007.tif (1652 kB)
S7 Fig. DRB2 and DRB4 form high molecular weight complexes.

journal.ppat.1006894.s008.docx (13 kB)
S1 Table. Mutant backgrounds used to express tagged DRB genes under their respective promoters.

journal.ppat.1006894.s009.docx (14 kB)
S2 Table. Epistatic analysis of F2 population derived from crosses between Di-17 and various wild-type or mutant lines.