Molecular Analysis of viviparous-1: An Abscisic Acid-Insensitive Mutant of Maize

The viviparous-1 (vp1) gene in maize controls multiple developmental responses associated with the maturation phase of seed formation. Most notably, mutant embryos have reduced sensitivity to the hormone abscisic acid, resulting in precocious germination, and blocked anthocyanin synthesis in aleurone and embryo tissues. The Vp1 locus was cloned by transposon tagging, using the Robertson's Mutator element present in the vp1-mum1 mutant allele. Detection of DNA rearrangements in several spontaneous and transposable element-induced mutant vp1 alleles, including a partial deletion of the locus, confirmed the identity of the clone. The Vp1 gene encodes a 2500-nucleotide mRNA that is expressed specifically in embryo and endosperm tissues of the developing seed. This transcript is absent in seed tissues of vp1 mutant stocks. Expression of C1, a regulatory gene for the anthocyanin pathway, is selectively blocked at the mRNA level in vp1 mutant seed tissues, indicating the Vp1 may control the anthocyanin pathway by regulating C1. We suggest that the Vp1 gene product functions to potentiate multiple signal transduction pathways in specific seed tissues.