Plant and Cell Physiology Advance Access originally published online on January 23, 2007
Plant and Cell Physiology 2007 48(3):424-433; doi:10.1093/pcp/pcm012
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Roles for the N- and C-Terminal Domains of Phytochrome B in Interactions Between Phytochrome B and Cryptochrome Signaling Cascades
1Department of Botany, Graduate School of Science, Kyoto University, Sakyo-Ku, Kyoto, 606-8502 Japan
*Corresponding author: E-mail, nagatani{at}physiol.bot.kyoto-u.ac.jp; Fax, +81-75-753-4126.
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Abstract |
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Plants fine-tune light responses through interactions between photoreceptors. We have previously reported that the greening of Arabidopsis thaliana roots is regulated synergistically by phytochromes and cryptochromes. In the present study, we investigated the functions of the N- and C-terminal domains of phytochrome B (phyB) in the interactions between phyB and cryptochrome signaling cascades. Transgenic Arabidopsis expressing the phyB N-terminal domain fused to green fluorescent protein (GFP), ß-glucuronidase (GUS) and the nuclear localization signal (NLS) showed intense root greening under blue light, indicating that the C-terminal domain was dispensable for the synergistic interaction in the induction of root greening. However, root greening under red light was substantially reduced in the absence of the C-terminal domain. This effect was opposite to the previous observation that removal of the C-terminal domain enhanced the signaling activity of phyB in the inhibition of hypocotyl elongation. In addition, we found that overexpression of the isolated C-terminal domain of phyB enhanced the blue light response not only for root greening but also for the inhibition of hypocotyl elongation. Analysis of this activity on various photoreceptor mutant backgrounds demonstrated that the isolated C-terminal domain enhanced cryptochrome signaling. In summary, these results demonstrate that different domains of phyB can play various roles which are dependent on light conditions as well as on the specific physiological response.
Keywords: Cryptochrome - Hypocotyl elongation - Photomorphogenesis - Photoreceptor interaction - Phytochrome - Root greening
Abbreviations: CG, phyB C-terminal domain fused to green fluorescent protein; CG–NES, phyB C-terminal domain fused to green fluorescent protein and a nuclear export signal; cry1, cryptochrome 1; cry2, cryptochrome2; GFP, green fluorescent protein; GUS, ß-glucuronidase; Ler, Landsberg erecta accession; MS, Murashige and Skoog; NES, nuclear export signal; NG–GUS–NLS, phyB N-terminal domain fused to green fluorescent protein, ß-glucuronidase and a nuclear localization signal; NLS, nuclear localization signal; PBG, full-length phyB fused to green fluorescent protein; phyA, phytochrome A; phyB, phytochrome B; PI, propidium iodide.
2Present address: Department of Plant Developmental Genetics, National Institute for Basic Biology, Okazaki, Aichi, 444-8585 Japan.
3Present address: Department of Plant Physiology, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602 Japan.
(Received October 20, 2006; Accepted January 17, 2007)
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