Abstract:
The objective of this study was to characterize the mitochondrial genomes of the species
within the genus Ceratocystis and investigate the evolutionary process of the ribosomal RNA
cistron found within these fungi. Ceratocystis incorporates a number of pathogenic species
affecting a variety of hosts, making the study of these fungi economically significant. The
fortuitous identification of a Ceratocystis species, C. manginecans, which contained two
different internally transcribed spacer sequence types within the ribosomal rRNA cistron,
enabled a study of concerted evolution in this fungus. Using this non-model organism we
were able to show empirical evidence for unequal crossing over and gene conversion as the
ultimate forces acting on this gene region dictating a concerted evolutionary effect. We
suggest that this process is true for all eukaryotes. Using the knowledge drawn from
previously characterized and annotated mitochondrial genomes of other eukaryotes, the
genomes of three Ceratocystis species, namely Ceratocystis fimbriata, Ceratocystis
albifundus and Ceratocystis moniliformis were fully assembled and annotated for
comparative analysis. This comparative study addressed the genome size, gene content,
tRNA presence as well as intron types and their homing endonucleases found among these
three mitochondrial genomes. An interspecies characterization was then undertaken using the
mitochondrial genomes of six different C. albifundus isolates from different geographical
locations in Africa. Genetic variation and similarities among these isolates supports the
previous hypothesis that the origin of this fungus is Southern Africa. It is hoped that the
research presented in this thesis will contribute to the improved understanding of the mitochondrial genomes in Ceratocystis species.
