Genetic (in)stability in tomato

Abstract

In the present study tomato lines carrying unstable alleles of the loci yv or sulfurea were characterized. In addition, we aimed at the isolation of an endogenous transposable element supposedly active in the unstable lines. Since the unstable loci were not cloned, we developed a transposon target system that enabled us to select for putative insertion mutants of the Adh-1 gene. While investigating the genetic characteristics of the Yv msand Sulfurea line it became apparent that the instability of their marker loci was not necessarily related to the activity of transposition elements. Also, the instability could not be related to the activity of tomato sequences homologous to transposable elements from related species. This invited speculation about the stability of DNA sequences in tomato. It is proposed that mechanisms which are known to underlie genetic instability in other organisms, have a role in the unstable expression of yv and sulfurea . These alternative mechanisms have been summarized in Chapter 1. Chapter 2 describes the isolation of an EMS induced Adh-1 null mutant and its use in crosses with the unstable tomato lines. In the resulting F 1 populations additional Adh-1 null mutants were selected through the resistance of seeds or pollen grains to allyl alcohol (Chapter 4). The cloning of the entire Adh-1 gene allowed the molecular analysis of the Adh-1 null mutants (Chapter 3). Chapter 5 describes the cytogenetic and genetic characterization of the tomato line Yvms. 'Me characteristics of a newly isolated unstable allele of the sulfurea locus are presented in chapter 6. Finally, chapter 7 describes the hybridization of tomato DNA to alien transposable element probes. These experiments emphasize the stability of transposable element-like sequences in the tomato genome