We have recently identified chloroplast-derived DNA sequences in an intron of a tomato nuclear gene that we had cloned. Although it had been demonstrated, by hybridization experiments, that the nuclear genomes of many plants contain sequences derived from the chloroplast genome, this is the first example of the physical isolation of such integrates. Our analysis of the integrates and of the integration sites suggests the involvement of homologous recombination mechanisms in the transposition events. In this proposal we outline experiments designed to physically isolate and characterize many chloroplast DNA integrates in the tomato nuclear genome. The date obtained will be used to test the hypothesis that homologous recombination is involved in the transposition of such chloroplast sequences into the nuclear genome. The presence of DNA sequences integrated into the cellular genome which originated in the organelle genomes has been abundantly documented. However, little or nothing is known about the mechanism(s) involved. The results of this study should provide insight into those processes.
