ANALYSIS OF FAST NEUTRON-GENERATED MUTANTS AT THE ARABIDOPSIS-THALIANA HY4 LOCUS

Ionizing radiation is expected to produce mutants with deletions or ot her chromosomal rearrangements. These mutants are useful for a variety of purposes, such as creating null alleles and cloning genes whose ex istence is known only from their mutant phenotype; however, only a few mutations generated by ionizing radiation have been characterized at the molecular level in Arabidopsis thaliana. Twenty fast neutron-gener ated alleles of the Arabidopsis HY4 locus, which encodes a blue light receptor, CRY1, were isolated and characterized. Nine of the mutant al leles displayed normal genetic behavior. The other 11 mutant alleles w ere poorly transmitted through the male gametophyte and were lethal in homozygous plants. Southern blot analysis demonstrated that alleles o f the first group generally contain small or moderate-sized deletions at HY4, while alleles of the second group contain large deletions at t his locus. These results demonstrate that fast neutrons can produce a range of deletions at a single locus in Arabidopsis. Many of these del etions would be suitable for cloning by genomic subtraction or represe ntational difference analysis. The results also suggest the presence o f an essential locus adjacent to HY4.