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

Abstract

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.

Integrated control of seed maturation and germination programs by activator and repressor functions of Viviparous-1 of maize.

“…We attribute the highly localized hydrolysis of the starchy endosperm underlying islands of vpl mutant aleurone cells to precocious induction and secretion of germination-specific hydrolytic enzymes in cells that have lost VP1 function. The sloped edges, which affect a halo of cells that are adjacent to the sector boundaries marked by the strictly cell-autonomous anthocyanin phenotype (McCarty et al 1989a), are consistent with the expected diffusion of the secreted hydrolytic enzymes. This implies strongly that like the anthocyanin pathway, the repression of the germination-specific hydrolase genes is cell autonomously controlled by VP 1.…”

“…The functions of ABI3 and VP1, however, diverge in so far that AB13 is required for seed dormancy in Arabidopsis whereas VP1 does not impose seed dormancy in maize. Because AB13 mRNA is stored in the dry seed (Parcy et al 1994)) whereas VP1 transcript and protein are essentially absent in the mature seed (McCarty et al 1989a;Carson 1993), we speculate that dormancy in Arabidopsis may reflect an extended timing of AB13 expression after seed maturity rather than a functional difference in the proteins. This view is supported by our results showing that overexpression of VP1 in aleurone of germinating maize seeds was effective in repressing Amy-GUS (Table 2).…”

“…The Vpl gene was cloned and shown to be expressed specifically in the developing seed (McCarty et al 1989a). It encodes a novel protein with a functional acidic transcriptional activation domain (McCarty et al 199 1 ).…”

Sugar-Hormone Cross-Talk in Anthocyanin Biosynthesis

“…In maize, viviparous-1 (vp1), an ABA insensitive mutant that fails to express the C1 gene (a MYB transcription factor similar to PAP1 and PAP2), shows no accumulation of anthocyanin (McCarty et al, 1989). In Arabidopsis seedlings, although ABA alone could induce PAP2, the hormone showed a synergistic effect with Suc on anthocyanin accumulation and caused a significant increase in the transcript levels of biosynthesis genes including CHS, DFR, LDOX, UF3GT, and C4H, among others (Loreti et al, 2008;Tonelli et al, 2007).…”

A general method to isolate genes tagged by a high copy number transposable element

“…Methylationsensitive restriction enzymes have been used, based on the idea that inactive elements are methylated thereby only visualizing active elements on genomic Southern blots (Chandler and Walbot, 1986). The mutation can also be outcrossed to a line that lacks transposable elements (McCarty et al, 1989) or tagged by two different transposable elements (O'Reilly et al, 1985).…”