The
viviparous-1 (vp1) locus in maize is a developmental gene that controls diverse aspects of the maturation phase of seed development. Mutations of
vp1 alter embryo sensitivity to the hormone abscisic acid and block formation of anthocyanin pigment. Molecular cloning of a Robertson Mutator-induced mutant allele,
vp1-mum-1, by transposable element tagging has allowed analysis of several transposon-induced
vp1 mutants. In the
vp1-Mc mutation, the gene is disrupted by 4.0 kbp insertion, which results in expression of a 3′ truncated mRNA. Phenotypically, this allele is at least partially functional in causing embryo dormancy, but is ineffective in controlling anthocyanin expression. This result suggests that disruption of the C-terminal domain of the
Vp1 protein specifically affects regulation of the anthocyanin pathway. A second
Mutator- derived allele,
vp1-mum2, exhibits an unusual form of somatic mutability in which endosperm cells revert from wild-type
vp1 expression to a mutant condition. The
vp1-mum2 allele contains a 1.5 kbp Insertion that has no detectable homology to known
Mu elements. This element is retained In wild-type germinal revertants derived from
vp1-mum2 An apparent DNA modification affecting cleavage at an internal Sstl restriction site in the element correlates with
vp1-mum2 states that exhibit wild-type
Vp1 expression. A model involving mitotic assortment of modified and unmodified DNA strands during development is proposed for
vp1-mum2 somatic mutation.
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