Quantification of dominance for proteins pleiotropically affected by opaque-2 in maize

Abstract

The maize opaque-2 (o2) mutation is known to have numerous pleiotropic effects. Using two different genetic backgrounds, endosperm proteins from isogenic lines of the o2 locus and their reciprocal hybrids were compared by high-resolution two-dimensional electrophoresis (2-D PAGE), and the 2-D gels stained with Coomassie blue or silver were analysed using a computer-assisted system for quantification of polypeptide spots. The aim of this work was (i) to identify polypeptides, the amount of which is affected by the single gene substitution, and (ii) to assess the dominance relations for every affected polypeptide. The triploid nature of the endosperm allowed the effects of 0, 1, 2 and 3 doses of the wild-type O2 allele to be examined. When using a basic pH range in the first dimension (IEF), we observed the known effects of o2 on prolamin storage proteins, mostly being 22 kDa, zeins. In a pH 5-7 IEF range, we detected 14 polypeptides whose amount is affected by the o2 mutation in both backgrounds. Eight of them were more abundant in the wild type than in the mutant and six were more abundant in the mutant than in the wild type. Dominance of the wild type allele was found for the amounts of 10 polypeptides, while the amounts of two of them displayed additive inheritance. This is an example where pleiotropically related characters display different inheritance, which could generate heterozygous phenotypes with original properties as compared to their homozygous parents. Because O2 belongs to the basic region-leucine zipper family of transcription activators, our results show that 2-D PAGE of isogenic lines represents a straightforward method to identify gene products affected by a transcription factor, whether they are products of its target genes, or products indirectly affected by far-reaching effects. This is a prerequisite to understanding the multiple molecular and physiological consequences of the action of such factors.