Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, Bower Building, University of Glasgow, Glasgow G12 8QQ, UK.
Photochem Photobiol Sci. 2018 Aug 8;17(8):1108-1117. doi: 10.1039/c8pp00138c.
The photoreceptor UV RESISTANCE LOCUS 8 (UVR8) activates photomorphogenic responses when plants are exposed to ultraviolet-B (UV-B) light. However, whereas the absorption spectrum of UVR8 peaks at 280 nm, action spectra for several photomorphogenic UV-B responses show maximal photon effectiveness at 290-300 nm. To investigate this apparent discrepancy we measured the effectiveness of UV wavelengths in initiating two responses in Arabidopsis: photoconversion of homodimeric UVR8 into the monomeric form, which is active in signaling, and accumulation of transcripts of the ELONGATED HYPOCOTYL 5 (HY5) transcription factor, which has a key role in UVR8-mediated responses. When purified UVR8 or Arabidopsis leaf extracts were exposed to UV light monomerisation was maximal at approximately 280 nm, which correlates with the UVR8 absorption spectrum. When intact plants were exposed to UV, monomerisation was most strongly initiated at approximately 290 nm, and this shift in maximal effectiveness could be explained by strong absorption or reflectance at 280 nm by leaf tissue. Notably, the action spectrum for accumulation of HY5 transcripts in the same leaf tissue samples used to assay UVR8 dimer/monomer status peaked at approximately 300 nm. Possible reasons for the difference in maximal photon effectiveness of UVR8 monomerisation and HY5 transcript accumulation in leaf tissue are discussed.
光受体 UV 抗性基因 8（UVR8）在植物暴露于紫外线-B（UV-B）光下时会激活光形态建成反应。然而，尽管 UVR8 的吸收光谱在 280nm 处达到峰值，但几种光形态建成 UV-B 反应的作用光谱在 290-300nm 处显示出最大的光子效率。为了研究这一明显的差异，我们测量了 UV 波长在引发拟南芥中两种反应中的有效性：同二聚体 UVR8 转化为单体形式的光转化，这在信号转导中是活跃的，以及 ELONGATED HYPOCOTYL 5（HY5）转录因子转录本的积累，该转录因子在 UVR8 介导的反应中具有关键作用。当纯化的 UVR8 或拟南芥叶片提取物暴露于紫外光下时，单体化在约 280nm 处达到最大值，这与 UVR8 的吸收光谱相关。当完整的植物暴露于 UV 下时，单体化在约 290nm 处最强地启动，这种最大有效性的偏移可以通过叶片组织在 280nm 处的强吸收或反射来解释。值得注意的是，同一叶片组织样本中用于检测 UVR8 二聚体/单体状态的 HY5 转录本积累的作用光谱在约 300nm 处达到峰值。讨论了叶片组织中 UVR8 单体化和 HY5 转录本积累的最大光子效率差异的可能原因。
