Tracing the evolutionary and developmental implications of mitochondrial genomic shifting in common bean

Maria de la Paz Arrieta-Montiel, Purdue University

Abstract

The plant mitochondrial genome consists of a population of variable sized molecules that inter-recombine at sites defined by pairs of directly oriented or inverted repeats. Substoichiometric levels of mitochondrial molecules has been widely reported in plants (Small et al., 1987; Susuki et al., 1996; Yesodi et al., 1995), and alterations in the mitochondrial genome resulting from copy number shifting of sub-genomic molecules have been observed in vitro (Hartmann et al., 1994; Vitart et al., 1992; Kanazawa et al., 1994;) and in vivo (Janska et al., 1998; Gutierrez et al., 1997). However, little is known about the biological significance of stoichiometric shifts within the mitochondrial genome, as well as the factors that control these shifts, the degree to which copy number changes, and the developmental consequences of the phenomenon. In common bean the cytoplasmic male sterility (CMS)-associated sequence pvs-orf239 appeared to be contained within an effectively dispensable sub-genomic mitochondrial molecule within the genome (Janska and Mackenzie, 1993). Stoichiometric shifting of the pvs-orf239 containing molecule occurs upon spontaneous reversion to fertility as well as the Fr-directed process of fertility restoration (Mackenzie and Chase, 1990; Janska et al., 1998). I used the common bean system to address the following questions. To what extent is copy number suppressed upon mitochondrial genomic shifting? To what extent does mitochondrial genome organization influence the shifting process? And finally, how is the high fidelity transmission of a complete mitochondrial genomic complement assured over generations? I present data suggesting that the change in stoichiometry of the pvs-orf239 sequence from a sterile (high copy number) to fertile (low copy number) state appears to be of at least three orders of magnitude in copy number and that the capacity of the common bean to shift the stoichiometry of the pvs-orf239 sequence seems to be influenced by the mitochondrial genome environment in which it is retained. Since substoichiometric forms of the mitochondrial genome can be retained with high fidelity throughout the evolution of a species, a model is discussed that accounts for their transmission based on the specific tissue that seems responsible for keeping the mitochondrial genome on its entirety.

Degree

Ph.D.

Advisors

Mackenzie, Purdue University.

Subject Area

Genetics|Molecular biology

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