| The three genomes of cucumber (Cucumis sativus) are differentially transmitted: maternally for plastids, paternally for mitochondria, and bi-parentally for the nucleus. A result of this unique attribute is that organellar effects can be separated by simple reciprocal crossing. When the highly inbred line 'B' is passed through cell cultures, paternally transmitted mosaic (MSC) phenotypes appear after regeneration and independently derived MSC lines possess different mitochondrial (mt) DNA conformations. MSC phenotypes have misshapen cotyledons, low germination rate, higher alternative oxidase levels, and lower ATP levels compared to inbred B. Next-generation sequencing revealed under-represented regions in mt DNAs of MSC lines 3, 12 and 16. Reverse-transcriptase quantitative PCR confirmed lower transcription of mitochondrial genes in these under-represented regions. However no consistent differences were detected for amounts of mitochondrial proteins encoded by genes in the under-represented regions, indicating that post-transcriptional events affect relative amounts of specific proteins.These results support cucumber as a model system to produce "knock-downs" of mitochondrial transcripts, and study nuclear responses in a highly inbred background. An example of a unique nuclear locus is Paternal Sorting of Mitochondria (Psm), which conditions the preferential sorting of wild-type mitochondria in progenies when MSC16 is used as the male parent. Psm was mapped to chromosome 3 of cucumber and a pentatricopeptide repeat was identified as the candidate gene controlling mitochondrial sorting in cucumber. This research demonstrates the usefulness of cucumber as a model plant to study nuclear-organelle interactions. |
