| Maternal transmission of cell organelles occurs in almost all angiosperms, but a few exceptions have been reported in banana, rapeseed, and cucumber (Cucumis sativus). Cucumber is unique in that the three plant genomes show different modes of transmission: nuclear DNA is transmitted bi-paternally, plastid DNA is transmitted maternally and mitochondrial DNA is transmitted paternally. The mosaic (MSC) phenotype of cucumber is associated with mitochondrial DNA deletions and rearrangements and is a valuable tool for studying mitochondrial transmission. Using MSC plants as males in crosses with diverse cucumber germplasms, a nuclear locus was revealed that controls sorting of the paternal mitochondrial DNA and designated as Paternal Sorting of Mitochondria (Psm). Amplified fragment length polymorphisms were used to assign the Psm locus to linkage group R of cucumber. Comparative mapping of cucumber and melon (Cucumis melo) provided additional markers near Psm and demonstrated that cucumber linkage group R is syntenic with linkage group G10 of melon. This is the first demonstration of synteny on the recombinational level between cucumber and melon. Due to the narrow genetic diversity between PI 401734 and Straight 8, only three codominant polymorphisms were identified that showed linkage to Psm. A wider cross in cucumber, coupled with the synteny between cucumber and melon, should reveal additional markers flanking Psm and may allow for its eventual cloning.;Cucumber possesses two attributes that may allow for mitochondrial transformation: the presence of a few, large mitochondria in microspores which could be the targets for biolistic transformation and paternal transmission of mitochondria which would deliver these transformed mitochondria to progenies. Working with Polish researchers, a mitochondrially targeted GFP was transformed into the nuclear genome of cucumber. PCR, Southern, and Western hybridizations confirmed expression of GFP in plants. Microscopic analyses of pollen from these transformed plants revealed that GFP was non-uniformally expressed in pollen, possibly due to the 35S promoter. GFP may not be an appropriate reporter gene for mitochondrial transformation of pollen due to the difficulty of visualizing this reporter in the pollen tubes. |
