Functional analysis of the UVR8 photoreceptor from the monocot Zea mays

Abstract

Low UV-B fluence is a signaling stimulus that regulates various physiological processes and induces photomorphogenic responses. The specific UV-B receptor UVR8, is a key component in these processes. Although UVR8 sequence is conserved, few homologs from plants have been cloned and reported to be functional. Here we show the cloning and functional analysis of Zea mays UVR8 (ZmUVR8) a monocotyledon species. ZmUVR8 has 73% of identity to AtUVR8. Key tryptophan responsible of UV-B perception are conserved, as well as the VP domain, involved in the interaction with the proteins COP1 and RUP1. Whereas UVR8 is expressed in non-irradiated of both Arabidopsis and maize leaves, after 2h of UV-B irradiation its expression was reduced. The expression of chalcone synthase (CHS) involved in flavonoid biosynthesis and regulated by UVR8, was increased in irradiated Arabidopsis and maize leaves. Arabidopsis uvr8-1 null mutant was complemented with ZmUVR8 driven by the CaMV-35S promoter and fused to eGFP. ZmUVR8-eGFP fusion was mainly localized in nuclei of transgenic lines, irrespective of UV-B treatments.Also, UV-B suppressed hypocotyl growth in WT Arabidopsis plants whereas uvr8-1 was impaired in this response. However, hypocotyl elongation was reduced in UV-B irradiated transgenic lines complemented with ZmUVR8. Moreover, CHS and transcription factor HY5 (ELONGATED HYPOCOTYL 5) expression were also restored in these plants. These results confirmed that ZmUVR8 is similar enough to AtUVR8 to restore UV-B perception and signaling in Arabidopsis mutant uvr8-1 being a functional UV-B photoreceptor.