Preliminary Study In The Stability Regulation Of Arabidopsis UV-B Photoreceptor

Light is a pivotal environmental factor which has a great influence on the growth and development of plants.Light is not only an energy source for plants,but also an informational signal that mediates various developmental processes ranging from seed germination to flowering.UV-B light(280-315 nm)induces plant photomorphogenesis and stress acclimation.UV RESISTANCE LOCUS 8(UVR8)has been identified as an UV-B photoreceptor that perceives UV-B light and initiates signal transduction.UV-B light induces UVR8 monomerization and nuclear accumulation.Monomeric UVR8 directly interacts with CONSTITUTIVELY PHOTOMORPHOGENIC 1(COP 1)to initiate signal transduction.However,it is not clear how UV-B light regulates the protein abundance of UVR8.Firstly,we treated YFP-UVR8/uvr8-6 with UV-B light for 0,6 and 24 h and examined UVR8 protein levels in the cotyledon,hypocotyl and root by confocal microscopy.We observed that UVR8 protein levels in the hypocotyl and root significantly reduced after UV-B light irradiation for 6 and 24 h.Then we treated plants with MG 132,and found that UV-B light induced UVR8 degradation in the hypocotyl and root.Among putative UVR8-interecting proteins we identified in Arabidopsis,ARABIDOPSIS SKP1 HOMOLOGUE 1(SKP1/ASK1)which is a subunit of E3 ubiquitin ligase was found to interacts with monomeric UVR8.Moreover,the overexpression of CULLIN 1(CUL1)and ASK1 resulted in reduced accumulation of UVR8.In cull-6 mutant,UVR8 protein remained relatively stable.These results suggest that extended exposure of UV-B light affects the stability of UVR8 in a tissue-specific manner,and that CUL1 and ASK1 are involved in this process.Secondly,to study the biological significance of the degradation of UVR8,we treated-UV-B-grown plants with UV-B light for 24 h,and found that CUL1 and ASK1 overexpressors displayed reduced inhibition of hypocotyl elongation.Moreover,the expression of UV-B responsive genes was up-regulated in cul1-6,but down-regulated in ASK1 and CUl1 overexpression lines.Taken together,this study reveals that UV-B light regulates UVR8 activity at a protein level,which helps us understand how plants respond to UV-B light.