The UV-B photoreceptor UVR8 promotes photosynthetic efficiency in Arabidopsis thaliana exposed to elevated levels of UV-B

Abstract

The UV-B photoreceptor UVR8 regulates expression of genes in response to UV-B, some encoding chloroplast proteins, but the importance of UVR8 in maintaining photosynthetic competence is unknown. The maximum quantum yield of PSII (F (v)/F(m)) and the operating efficiency of PSII (Φ(PSII)) were measured in wild-type and uvr8 mutant Arabidopsis thaliana. The importance of specific UVR8-regulated genes in maintaining photosynthetic competence was examined using mutants. Both F (v)/F(m) and Φ(PSII) decreased when plants were exposed to elevated UV-B, in general more so in uvr8 mutant plants than wild-type. UV-B increased the level of psbD-BLRP (blue light responsive promoter) transcripts, encoding the PSII D2 protein. This increase was mediated by the UVR8-regulated chloroplast RNA polymerase sigma factor SIG5, but SIG5 was not required to maintain photosynthetic efficiency at elevated UV-B. Levels of the D1 protein of PSII decreased markedly when plants were exposed to elevated UV-B, but there was no significant difference between wild-type and uvr8 under conditions where the mutant showed increased photoinhibition. The results show that UVR8 promotes photosynthetic efficiency at elevated levels of UV-B. Loss of the DI polypeptide is probably important in causing photoinhibition, but does not entirely explain the reduced photosynthetic efficiency of the uvr8 mutant compared to wild-type.

UV-B photoreceptor-mediated protection of the photosynthetic machinery in Chlamydomonas reinhardtii

“…Our findings, together with the recent description of a complementary role for PHOT in high-light activation of LHCSR3 expression (14), add a tier of regulation through anterograde signaling to the better-known feedback mechanisms operating within the chloroplast. In Arabidopsis, photoperception of UV-B by UVR8 is also important for the maintenance of photosynthetic competence, but the underlying mechanism in higher plants is not clear (35). It will be crucial for agricultural productivity and the biotechnological exploitation of photosynthetic processes to better understand the molecular mechanisms leading to photoprotection and reduced photoinhibition under sunlight and its intrinsic UV-B fraction.…”

“…In both Arabidopsis and Chlamydomonas, some of the UV-B-induced genes encode chloroplast proteins, and UV-B acclimation allows maintenance of photosynthetic efficiency under elevated levels of 35). However, a direct mechanistic link between UVR8 photoreceptor signaling and photoprotection of the photosynthetic machinery has remained unknown.…”

UV-B Perception and Acclimation in Chlamydomonas reinhardtii

“…The potential role of UVR8 UV-B signaling in photosynthesis is a current and interesting question. Recent work has begun to address this and has shown in Arabidopsis that UVR8 plays a role in maintaining photosynthetic efficiency under elevated UV-B (Davey et al, 2012). D1 protein levels were also investigated; however, the authors did not observe any difference in the magnitude of D1 protein decrease under UV-B between wild-type and uvr8 plants.…”

The UV-B Photoreceptor UVR8: From Structure to Physiology

“…UVR8 regulates additional genes, including those involved with other aspects of metabolism, signaling, and transcriptional regulation. Furthermore, several UVR8-regulated genes encode chloroplast proteins, which likely explains why uvr8 exhibits impaired capacity for photosynthesis compared with wild-type plants under elevated UV-B (Davey et al, 2012). A subsequent microarray analysis (Favory et al, 2009) indicated that several hundred genes are regulated by UVR8 in Arabidopsis seedlings, many in common with those regulated by UVR8 in leaf tissue (Brown et al, 2005).…”