Recently, Professor Hong-Quan Yang’s research team published a research article entitled “The COP1-ADA2b module mediates light regulation of DNA double-strand break repair in Arabidopsis” in Nature Communications. The study revealed the function of the light signaling master regulator COP1 as a negative regulator of DSB repair and uncovered its underlying molecular regulatory mechanism.
During the experiments, Arabidopsis thaliana seedlings were cultured on half-strength Murashige and Skoog (1/2 MS) medium supplemented with 1% sucrose and 0.8% agar. The seedlings were cultivated in a Jiupo plant growth chamber at 22°C under light conditions specified for each experiment.
Previous studies by Professor Yang’s team demonstrated that cryptochromes (CRYs) mediate blue light-induced DNA double-strand break (DSB) repair through ADA2b, and that ADA2b protein stability is regulated by blue light. Subsequent studies further confirmed that white light, red light, and far-red light all promote ADA2b accumulation, with these effects being mediated by CRYs (blue light signaling pathway) and phytochrome A/phytochrome B (phyA/phyB) (red/far-red light signaling pathways), respectively. The accumulation of ADA2b was significantly suppressed in corresponding double mutants.
To elucidate the mechanism underlying light-regulated ADA2b stability, the team performed biochemical experiments and demonstrated that COP1, a central negative regulator of light signaling and an E3 ubiquitin ligase, interacts with ADA2b, mediates its ubiquitination, and promotes its degradation through the 26S proteasome pathway.
Based on the role of ADA2b in DNA repair, the team further investigated the regulatory function of COP1 in DNA repair:
① The cop1-4 etiolated seedlings accumulated less endogenous DNA damage, suggesting that COP1 negatively regulates DNA damage repair.
② Following treatment with UV-C irradiation or DNA-damaging agents, cop1-4 mutants exhibited higher fresh weight under different light conditions and lower cotyledon bleaching rates after UV-C treatment. Their DNA damage resistance and survival rates were significantly higher than those of wild-type plants.
③ Under weak light conditions after MMS treatment, cop1-4 mutant nuclei exhibited fewer γ-H2AX foci, a marker of DSBs, and lower DNA damage levels in comet assays.
Collectively, these results demonstrate that COP1 acts as a negative regulator of DNA repair in plants.
The cop1-4 mutant exhibits enhanced resistance to DNA damage
Because ADA2b functions in DNA repair by recruiting SMC5 to DNA double-strand break sites, Professor Yang’s team further examined SMC5 recruitment in the cop1-4 and cop1-4 ada2b mutant backgrounds.
Consistent with previous findings that SMC5 recruitment depends on blue light and CRYs, under dark conditions, SMC5-YFP failed to form foci after MMS treatment in wild-type plants and remained diffusely distributed. However, under the same conditions, SMC5-YFP formed foci in the cop1-4 background, indicating partial restoration of SMC5 recruitment.
In contrast, in the cop1-4 ada2b double mutant, SMC5-YFP failed to form foci again, demonstrating that the constitutive recruitment of SMC5-YFP in cop1-4 plants under dark conditions depends on ADA2b.
Meanwhile, under white, blue, and red light conditions, MMS-treated cop1-4 mutants exhibited significantly higher relative fresh weight compared with wild-type plants, whereas the cop1-4 ada2b double mutants showed a phenotype similar to ada2b mutants, with significantly reduced relative fresh weight.
Comet assays further demonstrated that after MMS treatment in darkness, DNA damage accumulation in cop1-4 nuclei was lower than that in wild-type plants, while cop1-4 ada2b double mutants exhibited increased DNA damage accumulation similar to ada2b mutants.
Together, these results indicate that COP1 functions upstream of ADA2b to regulate DNA repair.
CRY and phyB mediate blue and red light signaling, respectively, to regulate DNA repair through the COP1-ADA2b module
Further genetic and biochemical analyses demonstrated that COP1 acts downstream of the photoreceptors CRY and phyB to mediate light-dependent regulation of DNA repair.
Blue light-activated CRYs and red light-activated phyB significantly weakened the interaction between COP1 and ADA2b. Similar to CRYs, phyB was also shown to interact with ADA2b and SMC5.
Under dark conditions, COP1 promotes ADA2b degradation and suppresses DNA repair. Under light conditions, activated photoreceptors such as CRYs and phyB inhibit COP1-mediated ADA2b degradation, thereby increasing ADA2b protein stability.
Meanwhile, through interactions with ADA2b and SMC5, CRYs and phyB further promote the recruitment of the SMC5/6 complex to DSB sites, enhancing ADA2b-mediated DNA repair.
Therefore, photoreceptors such as CRYs and phyB function as the “accelerator” to promote DSB repair, whereas COP1 acts as the “brake” by negatively regulating repair activity and ensuring that DNA repair is completed at an appropriate level and timing.
This dynamic regulatory mechanism enables plants to maintain genome stability under changing environmental conditions, thereby improving plant survival and environmental adaptability.
Author Information
Shanghai Normal University Ph.D. students Li Chen and Liman Diao are co-first authors of this paper. Associate Professor Tongtong Guo is the corresponding author, and Professor Hong-Quan Yang supervised the research.
Undergraduate student Jiaqi Ruan, graduate students Yanli Deng, Kai Zhang, and Yan Guan, as well as Associate Professor Ling Li from Shanghai Jiao Tong University, also contributed to this study.
This research was supported by funding from the National Natural Science Foundation of China (NSFC) General Program and the National Key Research and Development Program of China, among other projects.
Associate Professor Tongtong Guo guiding students during research