The localization of mitochondrial sequences to chromosomal DNA in orthopterans

There is growing evidence that the integration of mitochondrial DNA sequenc es into nuclear and chloroplast genomes of higher organisms may be widespre ad rather than exceptional. We report the localization of 18S-25S rDNA and mitochondrial DNA sequences to meiotic chromosomes of several orthopteran s pecies using in situ hybridisation. The cytochrome oxidase I (COI) sequence localizes to the centromeric and two telomeric regions of the eight bivale nts of Chorthippus parallelus, the telomeric regions in Schistocerca gregar ia and is present throughout the genome of Italopodisma sp. (Orthoptera: Ac rididae). The control region of the mitochondrion and COI localize to simil ar chromosomal regions in S. gregaria. These data explain sequencing data t hat are inconsistent with the COI sequence being solely mitochondrial. The different nuclear locations of mtDNA in the different genera studied sugges t that grasshopper mtDNA-like sequences have been inserted into the nuclear genome more than once in Acridid history, and there may have been differen t mechanisms involved when these events occurred in each of these species.