Mutations at the Shrunken Locus in Maize Caused by the Controlling Element DS

Abstract

Controlling elements in maize are transposable elements that cause insertion mutations, mediate chromosomal rearrangements and provide sites of chromosome breakage. Several distinct families of controlling elements have been identified, three of which have been studied in substantial detail genetically (for reviews, see McClintock, 1951, 1956b, 1965; Fincham and Sastry, 1974; Nevers and Saedler, 1977; Starlinger, 1980 and Fedoroff, 1982). Among the best characterized is the Activator-Dissociation family of elements that is responsible for the mutations at the Shrunken (Sh) locus described here (McClintock, 1951). Activator (Ac) is an element capable of autonomous transposition, while the Dissociation (Ds) element transposes only in the presence of the autonomously-transposing Ac element (McClintock, 1951). Ds was first identified and named for its ability to provide a specific site of chromosome breakage and acentric-dicentric chromosome formation, a property that is also manifested only in the presence of the Ac element (McClintock, 1946, 1947). Transposition of Ds to a locus affecting plant or kernel morphology can result in a recessive mutant phenotype (McClintock, 1951, 1956b). Ds insertion mutations are stable in the absence of Ac, but in its presence revert or further mutate both somatically and germinally.