Experimental evolutionary studies on the genetic autonomy of the cytoplasmic genome "plasmon" in the Triticum...

The term "plasmon" is used to indicate the whole cytoplasmic genetic system, whereas "genome" refers to the whole nuclear genetic system. Although maternal inheritance of the plasmon is well documented in angiosperms, its genetic autonomy from the coexisting nuclear genome still awaits critical examination. We tested this autonomy in two related studies: One was to determine the persistence of the genetic effect of the plasmon of Aegilops caudata (genome CC) on the phenotype of common wheat, Triticum aestivum strain "Tve" (genome AABBDD), during 63 y (one generation per year) of repeated backcrosses of Ae. caudata and its offspring with pollen of the same Tve wheat, and the second was to reconstruct an Ae. caudata strain from the genome of this strain and its plasmon that had been resident in Tve wheat for 50 generations, and to compare the phenotypic and organellar DNA characteristics between the native and reconstructed strains. Results indicated no change in the effect of Ae. caudata plasmon on Tve wheat during its stay in wheat for more than half a century, and no difference between the native and reconstructed caudata strains in their phenotype and simple sequence repeats in their organellar DNAs, thus demonstrating the prolonged genetic autonomy of the plasmon from the coexisting genomes of wheat and several other species that were used in the reconstruction of Ae. caudata The relationship between the proven genetic autonomy of the plasmon under changing nuclear conditions and its diversification during evolution of the Triticum-Aegilops complex is discussed.