Expression of photosynthetic genes is distinctly different between chloroplasts and amyloplasts in the liquid-cultured cells of sycamore (Acer pseudoplatanus L.).

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A nonphotosynthetic, white-wild cell line of sycamore (Acer pseudoplatanus L.) contains amyloplasts as the only kind of plastic!, whereas a photosynthetically competent green variant cell line contains only chloroplasts. Transcripts of both nuclear and plastid genes for photosynthetic components in the white cells were not detectable in contrast to those in the green cells. To investigate the limiting step (s) behind these diminished levels of transcripts, we have performed in vivo pulse-chase labeling of RNAin both cell types. These studies indicated that the rates of incorporation of [3H]uridine and nucleotide pool sizes were indistinguishable between the two cell lines. Transcripts of certain nuclear (rbcS, cab, psbO) and plastid (rbcL) genes in the white cell were not detectable. Weinfer from these data that transcriptional regulation entails an important role in controlling photosynthetic RNAlevels. Related analyses exploiting plastid run-on transcription have provided supporting evidence that the transcription of the amyloplast genomein the white cell is greatly suppressed in contrast to that of the chloroplast genomein the green cell. The results support a model of selective suppression of photosynthesis genes in nonphotosynthetic higher plant cells, and indicate that gene expression in such a system is primarily controlled at the transcriptional level.
日本細胞生物学会の論文