Protein Polymorphism Generated by Differential RNA Editing of a Plant Mitochondrial rps12 Gene

Abstract

The rps12 gene transcripts encoding mitochondrial ribosomal protein S12 are partially edited in petunia mitochondria. Different petunia lines were found vary in the extent of rps12 transcript editing. To test whether multiple forms of RPS12 proteins are produced in petunia mitochondria as a result of partial editing, we probed mitochondrial proteins with specific antibodies against edited and unedited forms of a 13-amino-acid RPS12 peptide spanning two amino acids affected by RNA editing. Both antibodies reacted with mitochondrial proteins at the expected size for RPS12 proteins. The amounts of unedited RPS12 protein in different petunia lines correlate with the abundance of unedited transcripts in these plants. Unedited rps12 translation products are also detected in other plant species, indicating that polymorphism in mitochondrial rps12 expression is widespread. Moreover, we show that RPS12 proteins recognized by both edited-specific and unedited-specific antibodies are present in a petunia mitochondrial ribosome fraction. These results demonstrate that partially edited transcripts can be translated and that the protein product can accumulate to detectable levels. Therefore, genes exhibiting incompletely edited transcripts can encode more than one gene product in plant mitochondria.

Coordination of Nuclear and Mitochondrial Genome Expression during Mitochondrial Biogenesis in Arabidopsis

“…Thus, it would be expected that the mitochondrially encoded proteins that are synthesized in excess and not assembled into complexes would be degraded by specific protease activities, such as the one described by Sarria et al (1998). This does not seem to be happening to the same extent in the case of ATP1, COB, and NAD9 (i.e., their abundance does not decrease as much as the abundance of the nuclear-encoded subunits of the same complexes), but results from other experimental plant systems (Lu et al, 1996) and yeast (reviewed in Rep and Grivell, 1996) suggest that rapid degradation of nonfunctional or unassembled mitochondrially encoded proteins seems to be the norm in mitochondria.…”

RNA editing: only eleven sites are present in the Physcomitrella patens mitochondrial transcriptome and a universal nomenclature proposal

“…In our study we could identify two of the eleven editing sites in P. patens mitochondria to be partially edited. A resulting protein heterogeneity from diVerentially edited RNAs was reported in one case (Lu et al 1996;Phreaner et al 1996) but not in others (Lu and Hanson 1994;Williams et al 1998). There is as yet no reasonable evidence for an additional level of modulating protein heterogeneity with physiological consequences through partially edited mRNAs.…”

Interactions of Mitochondrial and Nuclear Genes That Affect Male Gametophyte Development

“…There are a number of examples of RNA processing in restored lines of various species that results in the production of a monocistronic transcript of the linked mitochondrial gene. In a few CMS systems that feature essential genes within the CMS-associated region, the expression of a closely linked gene, such as petunia rps12 and maize atp4 (Prioli et al, 1993;Lu et al, 1996), has been examined at the protein level and found not to be abnormal. Similar analyses of the expression of the genes shown in many of the CMSassociated regions in Figure 1 wait to be performed.…”