Organ-specific nuclear RNAs in tobacco.

We investigated the developmental regulation of nuclear RNA sequences in tobacco vegetative (leaf, root, stem) and floral (petal, ovary, anther) organ systems using RNA-excess X single-copy DNA hybridization reactions. We found that 18% of the single-copy DNA, equivalent to 1.1 X 10(5) kilobases (kb) of diverse transcripts, is represented in the nuclear RNA of each organ. Each nuclear RNA population has both shared and organ-specific sequences. Depending upon the nuclear RNA, 10-40% of the complexity, or 1.1-4.4 X 10(4) kb of diverse sequence, is organ-specific. Collectively, at least 45% of the single-copy DNA, or 3 X 10(5) kb, is represented in the nuclear RNA of the entire plant. Hybridization experiments with polysomal RNA showed that organ-specific mRNAs are present in both the unique and shared nuclear RNA subsets. Together, our results show that tobacco nuclear RNA sequences are under striking developmental control and that both transcriptional and post-transcriptional processes play a role in regulating plant gene expression.