A Comprehensive Phylogeny Reveals Functional Conservation of the UV-B Photoreceptor UVR8 from Green Algae to Higher Plants

Abstract

Ultraviolet-B (UV-B) is present in sunlight (280–315 nm) and has diverse effects on living organisms. Low fluence rate of exposure induces a specific photomorphogenic response regulated by the UV-B response locus 8 (UVR8) receptor. UVR8 was first described in Arabidopsis thaliana. In the absence of stimuli it is located in the cytoplasm as a homodimer. However, upon UV-B irradiation, it switches to a monomer and interacts with the ubiquitin ligase E3 COP1 via the UVR8 β-propeller domain and the VP core. This induces the expression of the transcription factor HY5 leading to changes in the expression of genes associated with UV-B acclimation and stress tolerance. UVR8 senses UV-B through tryptophan residues being Trp233 and 285 the most important. Based on the comparison and analysis of UVR8 functionally important motifs, we report a comprehensive phylogeny of UVR8, trying to identify UVR8 homologs and the ancestral organism where this gene could be originated. Results obtained showed that Chlorophytes are the first organisms from the Viridiplantae group where UVR8 appears. UVR8 is present in green algae, bryophytes, lycophytes, and angiosperms. All the sequences identified contain tryptophans 233 and 285, arginines involved in homodimerization and the VP domain suggesting they are true UVR8 photoreceptors. We also determined that some species from bryophytes and angiosperms contain more than one UVR8 gene copy posing the question if UVR8 could constitute a gene family in these species. In conclusion, we described the functional conservation among UVR8 proteins from green algae to higher plants.

Photomorphogenic responses to ultraviolet‐B light

“…One question concerns the role of the UVR8 tryptophans. The 14 tryptophans in UVR8 are highly conserved in number and position in sequences from diverse species (Rizzini et al ; Wu et al ; Fernández et al ), but their functions are not entirely clear. There is evidence both from the crystal structure and mutant characterization that the ring of six tryptophans in the core of the protein helps to maintain the β‐propeller structure (O'Hara & Jenkins ).…”

“…Physcomitrella patens), lycophytes (e.g. the spike moss Selaginella moellendorffii) and both monocot and dicot Angiosperms (Rizzini et al 2011;Wu et al 2011;Fernández et al 2016). A study of the genome of the marine Angiosperm Zostera marina claims that UVR8 is not present (Olsen et al 2016), and this merits investigation at the protein level.…”

UVR8‐mediated induction of flavonoid biosynthesis for UVB tolerance is conserved between the liverwort Marchantia polymorpha and flowering plants

“…The UVR8 protein sequence is strongly conserved in the plant lineage (Rizzini et al ., ; Fernández et al ., ; Soriano et al ., ), and UVR8 of the Chlorophyceae green alga Chlamydomonas reinhardtii shows conservation of action with Arabidopsis UVR8 (Allorent et al ., ; Tilbrook et al ., ). Recently, Soriano et al .…”

Association between blooming time and climatic adaptation in Prunus mume

“…Most genes in this region are structural genes, and they might be involved in the blooming time or other processes related to blooming time. There is a receptor gene in the selective sweep regions, ultraviolet‐B receptor UVR8, that may receive environmental signals (Fernandez, Tossi, Lamattina, & Cassia, ). The UV‐B‐specific signaling component acts as a UV‐B photoreceptor and plays a key role in establishing UV‐protective responses in plants.…”