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bioRxiv · 10.1101/2025.07.16.665153

Conservation and divergence of UVR8-COP1/SPA-HY5 signaling in UV-B responses of Marchantia polymorpha

Liang, Y.·Podolec, R.·Chappuis, R.·Defossez, E.·Glauser, G.·Rötzer, J.·Stolze, S. C.·Dolan, L.·Nakagami, H.·Demarsy, E.·Ulm, R.
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Abstract

Ultraviolet-B radiation (UV-B) poses a major challenge to all forms of plant life. The liverwort Marchantia polymorpha (Marchantia) serves as a key model organism to study signaling pathways and to infer their evolution throughout the green lineage. Marchantia expresses key components of UV-B signaling, including the photoreceptor UV RESISTANCE LOCUS 8 (MpUVR8), the WD40-repeat protein REPRESSOR OF UV-B PHOTOMORPHOGENESIS (MpRUP), the E3 ubiquitin ligase complex CONSTITUTIVELY PHOTOMORPHOGENIC 1 / SUPPRESSOR OF phyA-105 (MpCOP1/MpSPA), and the transcriptional regulator ELONGATED HYPOCOTYL 5 (MpHY5). Here, we show that MpUVR8 exists as a homodimer in its ground-state in vivo, then monomerizes and accumulates in the nucleus upon UV-B activation. Activated MpUVR8 interacts with MpCOP1, triggering growth inhibition, genome-wide gene expression changes, biosynthesis of UV-absorbing metabolites, and photoprotection, which overall contributes to UV-B stress tolerance. MpRUP facilitates redimerization of MpUVR8 and Mprup null mutants show enhanced UV-B photomorphogenesis, demonstrating that MpRUP efficiently represses MpUVR8 signaling. Unlike the case in Arabidopsis and in contrast to the strong Mpcop1 mutant phenotype, Mpspa mutants develop only a very weak constitutive photomorphogenesis phenotype, indicating that COP1 function is much more independent of SPA in Marchantia than in Arabidopsis. Moreover, in contrast to Arabidopsis SPAs, Mpspa is linked with a hyper-responsive UV-B phenotype, suggesting that MpSPA is a negative regulator of MpUVR8 signaling. Similar to Arabidopsis HY5/HYH, MpHY5 functions antagonistically to MpCOP1, but its role in UV-B-mediated gene expression changes is more limited. Our findings demonstrate that although core components of UV-B signaling existed in the last common ancestor of extant land plants, regulatory interactions have diversified in different lineages since their divergence more than 400 million years ago.

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Liang, Y., Podolec, R., Chappuis, R., Defossez, E., Glauser, G., Rötzer, J., Stolze, S. C., Dolan, L., Nakagami, H., Demarsy, E., Ulm, R.. 2025-07-17. Conservation and divergence of UVR8-COP1/SPA-HY5 signaling in UV-B responses of Marchantia polymorpha. https://doi.org/10.1101/2025.07.16.665153

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