Conservation and divergence of UVR8 photoreceptor-mediated UV-B signaling in Marchantia polymorpha

The liverwort Marchantia (Marchantia polymorpha) serves as a key model organism for studying signaling pathways and inferring 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 whereas the core UVR8 photocycle is well conserved, regulatory roles of SPA and HY5 diverged during plant evolution. Unlike the case in Arabidopsis (Arabidopsis thaliana) and in contrast to the strong Mpcop1 mutant phenotype, Mpspa mutants developed only a very weak constitutive photomorphogenesis phenotype, indicating that COP1 function is much more independent of SPA in Marchantia than in Arabidopsis.