title: Sigma factor-mediated plastid retrograde signals control nuclear gene expression.
abstract: Retrograde signalling from plastids to the nucleus is necessary to regulate the organelle's proteome during the establishment of photoautotrophy and fluctuating environmental conditions. Studies that used inhibitors of chloroplast biogenesis have revealed that hundreds of nuclear genes are regulated by retrograde signals emitted from plastids. Plastid gene expression is the source of at least one of these signals, but the number of signals and their mechanisms used to regulate nuclear gene expression are unknown. To further examine the effects of plastid gene expression on nuclear gene expression, we analyzed Arabidopsis mutants that were defective in each of the six sigma factor (SIG) genes that encode proteins utilized by plastid-encoded RNA polymerase to transcribe specific sets of plastid genes. We showed that SIG2 and SIG6 have partially redundant roles in plastid transcription and retrograde signalling to control nuclear gene expression. The loss of GUN1 (a plastid-localized pentatricopeptide repeat protein) is able to restore nuclear (but not plastid) gene expression in both sig2 and sig6, whereas an increase in heme synthesis is able to restore nuclear gene expression in sig2 mutants only. These results demonstrate that sigma factor function is the source of at least two retrograde signals to the nucleus; one likely to involve the transcription of tRNA(Glu) . A microarray analysis showed that these two signals accounted for at least one subset of the nuclear genes that are regulated by the plastid biogenesis inhibitors norflurazon and lincomycin. Together these data suggest that such inhibitors can induce retrograde signalling by affecting transcription in the plastid.
authors.affiliation: Plant Biology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.
authors.forename: Jesse D
authors.initials: JD
authors.lastname: Woodson
authors.affiliation: Plant Biology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.|Howard Hughes Medical Institute, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Perez-Ruiz
authors.affiliation: Plant Biology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.|Howard Hughes Medical Institute, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.|Genomic Analysis Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schmitz
authors.affiliation: Plant Biology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.|Howard Hughes Medical Institute, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.|Genomic Analysis Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Ecker
authors.affiliation: Plant Biology Laboratory, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.|Howard Hughes Medical Institute, The Salk Institute, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.
authors.forename: Joanne
authors.initials: J
authors.lastname: Chory
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology; D002467:Cell Nucleus / Q000235:genetics / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D018087:Plastids / Q000502:physiology*; D036226:Seedlings / Q000235:genetics / Q000502:physiology; D012808:Sigma Factor / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; C519677:GUN1 protein, Arabidopsis; C000590916:SIG2 protein, Arabidopsis; C502611:SIG6 protein, Arabidopsis; D012808:Sigma Factor