Accelerating Mitochondrial Genome Evolution In Wheat

Mitochondria are centers of energy metabolism in the cell.  Nuclear-mitochondrial (NM) interactions in a cell are critical to all eukaryotes.  As plants cannot escape from adverse environmental conditions, high level of mitochondrial heteroplasmy and changes in frequencies of different mitotypes could play an important role in stress tolerance. We analyzed the NM interaction in an alloplasmic line of wheat (line with alien cytoplasm) having T. longissimum cytoplasm with T. durum nucleus and carrying a nuclear encoded Species Cytoplasm Specific (scs) gene influencing several developmental processes.  High resolution mapping by a combination of radiation hybrid and genetic mapping has narrowed the location of this locus to a small region with some exciting candidates explaining its role in Triticeae speciation.  Detailed sequence analysis of the mitochondrial genome in the same alloplasmic line revealed alteration of genome structure and gene expression patterns relative to parental lines. These changes are dramatic considering the generational timeframe. We also identified a high level of heteroplasmy in this alloplasmic line leading to increased variation possibly as a result of changing nuclear genome background.  Our analysis also indicates differential response of various alloplasmic wheat lines with the same nucleus to fungal pathogens Pyrenophoratritici-repentis (tan spot) and Puccinia triticina (leaf rust) providing additional evidence on the importance of cytoplasm to various plant development and stress response programming. Accelerating the mitochondrial genome evolution in plants by replacing the nucleus carrying compatible scs genes may provide a mechanism for generating altered morphological and/or stress responses.