title: Coordination of plastid protein import and nuclear gene expression by plastid-to-nucleus retrograde signaling.
abstract: Expression of nuclear-encoded plastid proteins and import of those proteins into plastids are indispensable for plastid biogenesis. One possible cellular mechanism that coordinates these two essential processes is retrograde signaling from plastids to the nucleus. However, the molecular details of how this signaling occurs remain elusive. Using the plastid protein import2 mutant of Arabidopsis (Arabidopsis thaliana), which lacks the atToc159 protein import receptor, we demonstrate that the expression of photosynthesis-related nuclear genes is tightly coordinated with their import into plastids. Down-regulation of photosynthesis-related nuclear genes is also observed in mutants lacking other components of the plastid protein import apparatus. Genetic studies indicate that the coordination of plastid protein import and nuclear gene expression is independent of proposed plastid signaling pathways such as the accumulation of Mg-protoporphyrin IX and the activity of ABA INSENSITIVE4 (ABI4). Instead, it may involve GUN1 and the transcription factor AtGLK. The expression level of AtGLK1 is tightly correlated with the expression of photosynthesis-related nuclear genes in mutants defective in plastid protein import. Furthermore, the activity of GUN1 appears to down-regulate the expression of AtGLK1 when plastids are dysfunctional. Based on these data, we suggest that defects in plastid protein import generate a signal that represses photosynthesis-related nuclear genes through repression of AtGLK1 expression but not through activation of ABI4.
authors.affiliation: The 21st Century Centers of Excellence Program, Cryobiofrontier Research Center, Iwate University, Morioka, Iwate 020-8550, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Kakizaki
authors.forename: Hideo
authors.initials: H
authors.lastname: Matsumura
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Nakayama
authors.forename: Fang-Sik
authors.initials: FS
authors.lastname: Che
authors.forename: Ryohei
authors.initials: R
authors.lastname: Terauchi
authors.forename: Takehito
authors.initials: T
authors.lastname: Inaba
mesh_terms: D021581:Active Transport, Cell Nucleus; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D010788:Photosynthesis; D018087:Plastids / Q000235:genetics / Q000378:metabolism*; D011524:Protoporphyrins / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: C470421:ABI4 protein, Arabidopsis; D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; C468867:GLK1 protein, Arabidopsis; C519677:GUN1 protein, Arabidopsis; D011524:Protoporphyrins; D018749:RNA, Plant; D014157:Transcription Factors; C039629:magnesium protoporphyrin