A constitutively monomeric UVR8 photoreceptor allele confers enhanced UV-B photomorphogenesis (bioRxiv)

In response to UV-B light, the plant UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) monomerizes and activates, inducing UV-B acclimation and survival. Re-dimerization by REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2 inactivates UVR8. In order to further clarify UVR8 pathway regulation, Podolec et al. analyzed Arabidopsis mutants with an aberrant hypocotyl phenotype when grown for 4 days under weak white light supplemented with UV-B. They discovered a novel hypersensitive uvr8 mutant allele, uvr8-17D, that harbors the UVR8^G101S protein variant which has a single glycine-101 to serine amino acid change. Seedlings of uvr8-17D showed enhanced UV-B acclimation and stress tolerance, which were associated with UVR8’s monomeric conformation in vivo, suggesting that re-dimerization by RUP1 and RUP2 is impaired and that UVR8^G101S remains active much longer than wild-type UVR8. This novel allele represents an exciting possibility to generate UV-B-hypersensitive phenotypes, including enhanced acclimation and UV-B tolerance, in other species by a single nucleotide substitution. (Summary by Elisandra Pradella @Elisandra_MP) bioRxiv 10.1101/2020.08.02.233007