INDUCTION OF UNSTABLE ALLELES AT THE TEMPERATURE-SENSITIVE VIRESCENT-1 GENE OF MAIZE USING THE TRANSPOSABLE ELEMENT DISSOCIATION

Transpositive mutagenesis was employed to prepare genetic strains usef ul in cloning the Virescent-1 locus (V1) of maize. A stepwise approach was used based on. (1) the isolation of putative insertion phenotypes (62 cases); (2) the verification of the genetic nature of the selecte d events (36 v1-m mutant alleles induced); (3) the accurate genetic st udy of 11 alleles; (4) the genetic assessment that the alleles v1-m1 a nd v1-m4 are due to the insertion of alpha Ds element into the locus V 1; (5) the proof that a Ds-like DNA element induces the inactivation o f the wild type function in the allele v1-m1. The phenotype of the uns table alleles, studied by germinating and keeping maize seedlings at t he temperature of 18 degrees C, are the following: alleles v1-m1, v1-m 9, v1-m11, v1-m17 and v1-m18 showing a few revertant green sectors on their leaves; v1-m4 exhibiting a reverse type of variegation; alleles v1-m2 and v1-m13 with a coarse pattern of variegation; alleles v1-m12, v1-m21 and v1-m23 frequently showing leaves part green with white str ipes and part white with green stripes. For the alleles studied, in ad dition to somatic instability, germinal reversions also occurred. In s ome cases, these reversions resulted in stable derivatives with a diff erent colour from that of the wild-type ('near green' or pale phenotyp es). The results presented not only allow the v1-m1 allele to be chose n as a starting material for cloning the V1 locus, but also define the molecular strategy to be followed.