The parental allelic ratio determines the DNA modification of the zein genes
--G. Lund and A. Viotti
The methylation state of the zein genes is presumed to correlate with the expression of these genes; i.e. the genes are heavily methylated in the embryo and demethylated in the endosperm (Bianchi, M and Viotti, A, Plant Mol. Biol. 11:203-214, 1988). We have investigated whether these genes are subjected to genomic imprinting.
Genomic DNA extracted from embryo and endosperm of the three inbred lines A69Y, W22 and W64A, and the reciprocal crosses between all three inbred lines, was digested with the methylation sensitive enzymes PvuII and HhaI, followed by Southern blotting and hybridization to cDNA and genomic clones of the heavy- and light-chain genes zA1 and zE19.
The results show that the family of zein genes belonging to zA1 and zE19 are demethylated in the endosperm, and that the pattern of demethylation is dependent only on the contribution of the maternal genome. Furthermore, the pattern of demethylation is a conserved feature of the investigated lines, as identical patterns are observed between DNA from different maize harvests. The CpG- and CpNpG- methylation does not have a differential role as far as genomic imprinting is concerned, as identical results were obtained from the digestions of DNA using PvuII and HhaI, which recognize CpNpG- and CpG sequences respectively.
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