Summary
Low UV-B fluence is a signalling stimulus that regulates various metabolic and developmental processes, and induces a photomorphogenic response. The specific UV-B receptor UV-B response locus 8 (UVR8) is a key component of this response.
UVR8 and several proteins participating in the UVR8 signalling were first cloned in Arabidopsis. Although UVR8 sequence is conserved, a few UVR8 homologs has been cloned and reported to be functional from green algae, moss and dicots.
Here we show the cloning and functional analysis of Zea mays UVR8 (ZmUVR8). ZmUVR8 has 443 amino acid length, a calculated molecular mass of 47.15 kDa, and 73% of identity to AtUVR8. Key trypthophan residues responsible of UV-B perception (W233, 285 and 337) are conserved in ZmUVR8, as well as the VP domain in the C27 region, involved in the interaction with the proteins COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1) and RUP1 (Repressor of UV-B photomorphogenesis 1). Blastp analysis shows that all the components of Arabidopsis UVR8 pathway were present in maize.
UVR8 was expressed in non-irradiated Arabidopsis and maize plants. However, after 2h of UV-B irradiation, AtUVR8 expression was reduced 3-fold, and ZmUVR8 expression was reduced 6-fold. That indicate a similar regulation of UVR8 expression under UV-B treatment in Arabidopsis and maize.
Arabidopsis uvr8 mutant was complemented with ZmUVR8 driven by the CaMV-35S promoter and fused to eGFP (35S::ZmUVR8-eGFP). Whereas UV-B stimulates GFP-UVR8 nuclear accumulation in Arabidopsis, ZmUVR8-GFP fusion was mainly localized in nuclei of transgenic lines, irrespective of UV-B treatments.The hypocotyl length inhibition, is the most commonly phenotype analyzed to investigate the functions of photoreceptors in Arabidopsis. UV-B suppressed hypocotyl growth in wild-type Arabidopsis plants whereas uvr8-1 was impaired in this response. Hypocotyl elongation was reduced in 35S::ZmUVR8-eGFP lines. These results confirmed that ZmUVR8 is similar enough to AtUVR8 to restore UV-B perception and signalling in Arabidopsis and thus is a functional UV-B photoreceptor