Organ-specific transcription of the rrn operon in spinach plastids.
The spinach rrn operon is used as a model system to study transcriptional regulation in higher plant photosynthetic and non-photosynthetic plastids. We performed capping experiments to determine whether P1, PC, or P2 promoters are employed for rrn transcription start sites in cotyledon and root tissues. By using a new method of analysis of capped RNA we demonstrate for the first time that 1) in both organs the rrn operon is expressed in a constitutive manner by cotranscription with the preceding tRNA(GAC)Val gene, and 2) the PC transcription start site is used only in cotyledons and leaves, i.e. we demonstrate the organ-specific usage of a plastid promoter. Both start sites, PC and that of the tRNA(GAC)Val cotranscript, lack Escherichia coli-like consensus sequences. The cotranscript is initiated 457 base pairs upstream of the tRNA(GAC)Val gene. The PC-specific DNA-binding factor, CDF2, is not detectable in root tissues confirming its regulatory role in PC-initiated rrn expression and the organ specificity of PC expression. Furthermore, our results show that rrn operon expression patterns differ in spinach and tobacco indicating species-specific transcriptional regulation of plant plastid gene expression.
Iratni
R
R
Laboratoire de Génétique Moléculaire des Plantes, Université Joseph Fourier and CNRS, B. P. 53, F-38041 Grenoble, France.
Diederich
L
L
Harrak
H
H
Bligny
M
M
Lerbs-Mache
S
S
D001483:Base Sequence; D001665:Binding Sites; D018744:DNA, Plant / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010947:Plants, Toxic; D018087:Plastids / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012366:RNA, Transfer, Val / Q000235:genetics; D016914:Ribonuclease H / Q000378:metabolism; D013045:Species Specificity; D018724:Spinacia oleracea / Q000235:genetics* / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics; D014158:Transcription, Genetic; D012407:rRNA Operon / Q000235:genetics*
D018744:DNA, Plant; D004268:DNA-Binding Proteins; D012336:RNA, Ribosomal, 16S; D012366:RNA, Transfer, Val; D016914:Ribonuclease H