Regulating Red and Blue Light Responses

Abstract

Plants detect and respond to changes in light quantity and quality. Phytochromes detect red light and crytochromes detect blue light. Ward et al. report the identification of a mutation sob1-D ( suppressor of phyB-4 dominant ), which corresponds to the previously named gene OBP3 , that is involved in both red light and blue light responses. OBP3 was identified in an activation-tagging screen, which identifies gain-of-function mutants, by its ability to inhibit the long hypocotyl phenotype of a phytochrome mutant phyB-4 . OBP3 was overexpressed in the sob1-D , phyB-4 mutant plants. OBP3 encodes a putative transcription factor of the Dof (DNA binding with one finger) family. RNAi was used to decrease OBP3 levels, and OBP3-RNAi plants were larger than the OBP3-overexpressing plants, which are dwarfs. OBP3-RNAi plants also exhibited a slight, but significant, increase in hypocotyl length when grown in white light compared with wild-type plants, and this response required wild-type or partially functional phyB but was lost in phyB-null plants. OBP3-RNAi plants also exhibited larger cotyledons than wild-type plants when grown in white light due to an increase in the size of the epidermal cells. The increase in cotyledon size observed in the OBP3-RNAi plants was greatest for plants grown in blue light, and this response was only observed when wild-type or partially functional cry1 (a blue light-sensing cryptochrome) was present. Thus, OBP3 appears to participate as a negative regulator of cry1-mediated cotyledon expansion and as a positive regulator of phyB-mediated inhibition of hypocotyl elongation. J. M. Ward, C. A. Cufr, M. A. Denzel, M. M. Neff, The Dof transcription factor OBP3 modulates phytochrome and cryptochrome signaling in Arabidopsis. Plant Cell 17 , 475-485 (2005). [Abstract] [Full Text]