Rice RING E3 ligase may negatively regulate gamma-ray response to mediate the degradation of photosynthesis-related proteins
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In this study, our findings regarding the regulation of GA irradiation-induced OsGIRP1 in relation to the levels of photosynthesis-related proteins such as OsrbcL1 and OsrbcS1 and hypersensitive responses of overexpressing plants to GR irradiation provide insight into the molecular functions of OsGIRP1 as a negative regulator in response to the stress of radiation.
The RING (Really Interesting New Gene) finger proteins are known to play crucial roles in various abiotic stresses in plants. Here, we report on RING finger E3 ligase, Oryza sativa gamma rays-induced RING finger protein1 gene (OsGIRP1), which is highly induced by gamma rays (GR) irradiation. In vitro ubiquitination assay demonstrated that a single amino acid substitution (OsGIRP1C196A) of the RING domain showed no E3 ligase activity, supporting the notion that the activity of most E3s is specified by a RING domain. We isolated at least 6 substrate proteins of OsGIRP1, including 2 Rubisco subunits, OsrbcL1 and OsrbcSl, via yeast two-hybridization and bimolecular fluorescence complementation assays. OsGIRP1 and its partner proteins were targeted to the cytosol and the cytosol or chloroplasts, respectively; however, florescence signals of the complexes with OsGIPR1 were observed in the cytosol. Protein degradation in cell extracts showed that OsGIRP1 mediates proteolysis of 2 substrates, OsrbcS1 and OsrbcL1, via the 26S proteasome degradation pathway. The Arabidopsis plants overexpressing OsGIRP1 clearly exhibited increased sensitivity to GR irradiation. These results might suggest that OsGIRP1 acts as a negative regulator of GR response to mediate the degradation of photosynthesis-related proteins.
Keywords26S proteasome Gamma rays RING E3 ligase Rubisco subunits Ubiquitination
Really interesting new gene
Bimolecular fluorescence complementation
Ribulose biphosphate carboxylase/oxygenase
Synthetic defined medium lacking Leu and Trp supplemented with 40 μg ml−1 X-α-Gal and 70 ng ml−1 aureobasidin A (AbA)
Synthetic defined medium lacking Ade, His, Leu, and Trp with 40 μg ml−1 X-α-Gal and 70 ng ml−1 AbA
This work was supported by the National Research Foundation of Korea Funded by the Ministry of Education, Science, and Technology (NRF-2013R1A1A4A01011064) and by grants from the Nuclear R&D Program of the Ministry of Science, ICT, and Future Planting (MSIP), Republic of Korea.
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