Elevating Cytoplasmic Diversity: A Promising Strategy for Wheat Germplasm Enhancement.

Genetic variability for economic traits is critical for crop improvement. For decades, nuclear genome diversity was the main focus of genetic studies and breeding selection whereas cytoplasmic diversity was ignored. However several crucial physiological traits of plants, including photosynthesis, carbon assimilation, apoptosis and energy production, are controlled at least partially, by chloroplast and mitochondria. Past studies reported that cytoplasmic diversity is considerably narrow in Triticum genus. To improve this diversity, various cytoplasm types from different Aegilops species have been introduced into common (Triticum aestivum L.) and durum (T. turgidum) wheat nuclei. This study focused on ATP synthase subunit 6 gene sequence for diversity analysis as a polymorphism hotspot within cytoplasmic genomes of Triticum-Aegilops complex. This gene provides a crucial inner membrane channel that couples proton gradient to ATP production in the mitochondria of all eukaryotes. Mitochondrial genome of 46 different alloplasmic and euplasmic lines were first isolated and their ATP6 gene was sequenced by the Sanger method. Sequence alignment and subsequent cladogram were constructed using ClustalX2 and phangorn package, respectively. Results allowed to show that construction of normal wheat cultivars harboring alien cytoplasm drastically elevate the genetic diversity in their cytoplasm.  Four major ATP6 orthologs have been detected from which two are reported for the first time. This evidence indicates the existence of a vast amount of polymorphism in this region that may be the result of homologous recombination within the mitochondrial genome. We also demonstrated that increasing the cytoplasmic diversity is associated with phenotypic variation. Several economically important traits were affected by cytoplasmic genomes including biomass, supernumerary spikelet, heading time and protein content. These cytoplasmic genetic variability provide a unique opportunity for breeders to improve several economic including agronomic and quality traits.