title: Dual temporal role of plastid sigma factor 6 in Arabidopsis development.
abstract: Plants contain nuclear-coded sigma factors for initiation of chloroplast transcription. The in vivo function of individual members of the sigma gene family has become increasingly accessible by knockout and complementation strategies. Here we have investigated plastid gene expression in an Arabidopsis (Arabidopsis thaliana) mutant with a defective gene for sigma factor 6. RNA gel-blot hybridization and real-time reverse transcription polymerase chain reaction together indicate that this factor has a dual developmental role, with both early and persistent (long-term) activities. The early role is evident from the sharp decrease of certain plastid transcripts only in young mutant seedlings. The second (persistent) role is reflected by the up- and down-regulation of other transcripts at the time of primary leaf formation and subsequent vegetative development. We conclude that sigma 6 does not represent a general factor, but seems to have specialized roles in developmental stage- and gene-specific plastid transcription. The possibility that plastid DNA copy number might be responsible for the altered transcript patterns in mutant versus wild type was excluded by the results of DNA gel-blot hybridization. Retransformation of the knockout line with the full-length sigma 6 cDNA further established a causal relationship between the functional sigma gene and the resulting phenotype.
authors.affiliation: Plant Cell Physiology, University of Bochum, D-44780 Bochum, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Loschelder
authors.forename: Jennifer
authors.initials: J
authors.lastname: Schweer
authors.forename: Brigitte
authors.initials: B
authors.lastname: Link
authors.forename: Gerhard
authors.initials: G
authors.lastname: Link
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018744:DNA, Plant / Q000378:metabolism; D017353:Gene Deletion; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D005816:Genetic Complementation Test; D009154:Mutation; D018087:Plastids / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; C502611:SIG6 protein, Arabidopsis; D012808:Sigma Factor