Shade-induced ROS/NO reinforce COP1-mediated diffuse cell growth

Since the photosynthetic apparatus produces reactive oxygen species (ROS), shade was predicted to reduce ROS. In contrast, in the hypocotyl of Arabidopsis seedlings, shade enhanced the generation of ROS and nitric oxide (NO). Sensory perception of shade enhances auxin synthesis and auxin was the trigger of ROS and NO accumulation. The resulting nitroxidative environment favored the S-nitrosylation (posttranslational modification) of proteins such as CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1), which is fundamental for the hypocotyl growth response to shade. Impairing COP1 S-nitrosylation either genetically or pharmacologically not only reduced the diffuse growth of hypocotyl cells exposed to shade, but it also distorted their coordination causing hypocotyl bending. This study reveals an unexpected ROS/NO regulation of shade avoidance.