Phytochrome regulates translation of mRNA in the cytosol.
An array of photoreceptors including cryptochromes, phototropin, and phytochromes regulates various light responses in plants. Among these photoreceptors, phytochromes perceive red and far-red light by switching between two interconvertible spectral forms (Pr and Pfr). The Pfr form promotes light responses partly by destabilizing negatively acting, phytochrome-interacting basic helix-loop-helix transcription factors (PIFs), thus modulating transcription in the nucleus. The Pfr form is also present in the cytosol. However, the role of phytochromes in the cytosol is not well understood. Here we show that the Pfr form interacts with the cytosolic protein PENTA1 (PNT1) and inhibits the translation of protochlorophyllide reductase (PORA) mRNA. PNT1 possesses five C3H-type zinc finger domains and displays similarity to various RNA binding proteins including Tristetraprolin, which regulates stabilities of mRNAs such as TNF-α mRNA in humans. Consistent with its function as an RNA binding protein, PNT1 directly binds to mRNA of a key chlorophyll biosynthetic gene, protochlorophyllide reductase in vivo and inhibits the translation of PORA mRNA in the presence of phytochromes. The present results demonstrate that phytochromes transmit light signals to regulate not only transcription in the nucleus through PIFs, but also translation in the cytosol through PNT1.
Department of Biological Sciences,  Korea Advanced Institute of Science and Technology, Daejeon 305-701,  Korea.
Inyup
I
Paik
Seungchan
S
Yang
Giltsu
G
Choi
D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D016000:Cluster Analysis; D003600:Cytosol / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology*; D008156:Luciferases; D008364:Mannosyltransferases / Q000235:genetics / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000235:genetics / Q000378:metabolism*; D038761:Photobleaching; D010802:Phylogeny; D010834:Phytochrome / Q000378:metabolism* / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020798:Two-Hybrid System Techniques
D029681:Arabidopsis Proteins; D017931:DNA Primers; D012333:RNA, Messenger; D010834:Phytochrome; D008156:Luciferases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; D008364:Mannosyltransferases; C507149:PNT1 protein, Arabidopsis