Poster: Late and Moved Abstracts

Abs # 1414: Identification of RNA Editing Sites in Chloroplast Transcripts from Nicotiana species

Presenter:	Sasaki, Tadamasa , t.sasaki@nsc.nagoya-cu.ac.jp
Authors	Sasaki, Tadamasa  (A)   Yasushi, Yukawa  (A)   Tetsuya, Miyamoto  (B)   Junichi, Obokata  (B)   Masahiro, Sugiura  (A)
Affiliations:	(A): Graduate School of Natural Sciences, Nagoya City University (B): Center for Gene Research, Nagoya University

RNA editing alters genomic nucleotide sequences at the transcript level. In higher plants, C-to-U conversion (rarely U-to-C) is known to occur at around 30 sites in chloroplast transcripts and at several hundred positions in mitochondrial mRNAs. The tobacco cultivar Nicotiana tabacum is an amphydiploid (4n) derived from the two progenitors N. sylvestris (2n, maternal) and N. tomentosiformis (2n, paternal). The chloroplast genome of N. tabacum is believed to originate from N. sylvestris. In order to study the origin and evolution of RNA editing in higher plant chloroplasts, identification of editing sites among the three Nicotiana species has been made. Direct sequencing of cDNAs derived from the transcripts of these Nicotiana plants was carried out to search for editing sites. Thirty-four, 33 and 32 editing sites were found in the transcripts from N. tabacum, N. sylvestris and N. tomentosiformis, respectively. Most sites are conserved among the three species, whereas a limited number of sites differ in these species. A remarkable difference was observed in the editing of ndhB and ndhD transcripts. Sites 7 and 8 in ndhB mRNAs are separated only by five nt, and both are edited in N. tabacum and N. sylvestris. However, site 8 is not edited in N. tomentosiformis, indicating that distinct trans-factors are involved in the two editing events. The first site in ndhD mRNAs is edited to produce an AUG start codon in N. sylvestris as well as in N. tabacum but not in N. tomentosiformis, suggesting that a distinct mechanism operates for the translational initiation of N. tomentosiformis ndhD mRNAs.