C-to-U conversion in the intercistronic ndhI/ ndhG RNA of plastids from monocot plants: conventional editing in an unconventional small reading frame?
Editing of plastid RNAs proceeds by C-to-U, in hornwort species also by extensive U-to-C, transitions, which predominantly lead to the restoration of codons for structurally and/or functionally important, conserved amino acid residues. So far, only one instance of editing outside coding regions has been reported - in the psbL/ psbF intergenic region of Ginkgo biloba. This site was proposed to have no functional importance. Here we present an evaluation of an editing site in the ndhI/ ndhG intergenic region in a related group of monocot plants. Efficient editing of this site, as well as the phylogenetic conservation of the resulting uridine residue, point at an important role for the sequence restored by editing. Two potential functions can be envisaged. (1) RNA secondary structure predictions suggest that the C-to-U conversion at this site can lead to a modified stem/loop structure of the ndhG 5' UTR, which could influence ndhG expression. (2) Alternatively, editing of the ndhI/ ndhG intergenic region may tag a so far unidentified small (12-codon) ORF, and lead to the restoration of a conserved phenylalanine codon. A screen with specific antibodies elicited against the putative peptide failed to detect such a peptide in chloroplast fractions. However, this failure may be attributable to its low and/or development-specific expression.
Drescher
A
A
Botanisches Institut der Ludwig-Maximilians-Universität München, Menzingerstr. 67, 80638, Germany.
Hupfer
H
H
Nickel
C
C
Albertazzi
F
F
Hohmann
U
U
Herrmann
R G
RG
Maier
R M
RM
D000595:Amino Acid Sequence; D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D005796:Genes; D017343:Genes, Plant; D019684:Magnoliopsida / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009245:NADH Dehydrogenase / Q000235:genetics; D009690:Nucleic Acid Conformation; D018087:Plastids / Q000235:genetics; D017393:RNA Editing; D018749:RNA, Plant / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016364:Reading Frames; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D018744:DNA, Plant; D018749:RNA, Plant; D009245:NADH Dehydrogenase