Gamma-Zein Content is Ralated to Endosperm Modification in Quality Protein Maize
Opaque-2 (o2) is a mutation in one of the regulatory loci that control storage protein gene transcription in maize (Zea mays L.) kernels. It results in a significant reduction in the prolamine content of the endosperm, which becomes chalky and soft. Quality Protein Maize (QPM) genotypes are modified, hard-endosperm, o2 mutants that carry genetic factors responsible for increased synthesis of the γzein protein (tool. wt. 27 kD). The genes encoding this storage protein are not under regulatory control of the 02 locus. We used a combination of genetic and biochemical analyses to investigate the relationships between endosperm modification and γ-zein content in QPM. The use of unmodified and modified genotypes allowed us to demonstrate, by reciprocal crosses and F2 segregating progenies, that degree of vitreousness and increased synthesis of γ-zein in modified endosperms are both dosage dependent and directly correlated. Additionally, we found that these same genetic factors are active in other soft-endosperm mutants such as floury-2 (fl2), and floury-2;opaque-2 (fl2;o2), as well as in normal inbred lines. Although endosperm modification appears to be the result of a genetically complex system, its primary effect appears to be on the synthesis of the γ-zein protein. Our studiesuggest that there may be a relationship between the high content of this protein and increased kernel vitreousness in QPM.
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