ALTERED MITOCHONDRIAL GENE-EXPRESSION IN A MATERNAL DISTORTED LEAF MUTANT OF ARABIDOPSIS INDUCED BY CHLOROPLAST MUTATOR

chloroplast mutator (chm) of Arabidopsis is a recessive nuclear mutati on that causes green and white variegation in leaves and is inherited in a non-Mendelian fashion. In this study, we have identified and char acterized a mutant observed in F-1 and backcrossed BC1 populations fro m a cross between chm1-3 and ecotype Columbia. This mutant, maternal d istorted leaf (MDL), grows very poorly and is distinguished by distort ed rough leaves and aborted flowering organs. Electron microscopic obs ervation showed that in MDL plants, a significant portion of mitochond ria are abnormal and appear to be nonfunctional. DNA gel blot end sequ ence analysis of the MDL mitochondrial DNA (mtDNA) revealed rearrangem ents in two mtDNA fragments associated with rps3-rpl16 genes (encoding ribosomal proteins S3 and L16, respectively). One rearrangement resul ted in the insertion of the rps3-rpl16 operon downstream of atp9. An i ndependent deletion in this region had eliminated the majority of rps3 . In contrast, another rearrangement deleted part of rpl16, whereas rp s3 remained intact. RNA gel blot analysis indicated that expression of these genes is also altered as a consequence of the mtDNA rearrangeme nts. Thus, a mutation at the CHM locus affects mitochondrial gene expr ession, and impaired mitochondrial function may result in the distorte d phenotype.