Plant Cell. 2004 Jul;16(7):1707-16. Epub 2004 Jun 11.
Allelic variation of gene expression in maize hybrids.
Guo M, Rupe MA, Zinselmeier C, Habben
J, Bowen BA, Smith OS.
Abstract
Allelic expression variation of nonimprinted autosomal genes has
recently been uncovered in mouse hybrids and humans. The allelic expression
variation is attributed to differences in noncoding DNA sequences and does not
involve epigenetic regulation or gene imprinting. This expression variation is
suggested to play important roles in determining phenotypic diversity.
Virtually nothing is known about such allele-specific expression variation in a
hybrid plant where two alleles are compared in the same genetic context. We
examined parental transcript accumulation in maize (Zea mays) hybrids
using allele-specific RT-PCR analysis. Among 15 genes analyzed, 11 showed
differences at the RNA level, ranging from unequal expression of the two
alleles (biallelic) to expression of a single allele (monoallelic). Maternal or
paternal transmission had little effect on the allele-specific transcript ratio
of nearly all genes analyzed, suggesting that parent-of-origin effect was
minimal. We analyzed the allelic difference in genetically contrasting hybrids
and hybrids under high planting density and drought stress. Whereas a
genetically improved modern hybrid expressed both alleles, a less improved old
hybrid frequently showed mono-allelic expression. Furthermore, the two alleles
in the hybrid responded differentially to abiotic stresses. The results of
allele-specific regulation in different tissues in responding to environment
and stress suggest an unequivalent function of the parental alleles in the
hybrid, which may have an impact on heterosis.