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Zusammenfassung:
F1-hybrids are more vigorous than their homozygous, genetically distinct parents, a phenomenon known as heterosis. In the past it was demonstrated that already the young root system shows heterosis. However, the molecular mechanisms underlying the manifestation of heterosis are only poorly understood. In the present study, the transcriptomes of the reciprocal maize (Zea mays L.) hybrids B73xMo17 and Mo17xB73 and their parental inbred lines B73 and Mo17 were surveyed in primary roots early in the developmental manifestation of heterosis. The application of novel and robust statistical approaches and a suitable experimental design established that 34,233 (i.e., 86%) of all high-confidence maize genes were expressed in at least one genotype. Consistent with the dominance model (i.e., complementation) for heterosis 1,124 genes that were expressed in the hybrids were expressed in only one of the two parents, a pattern that was termed single parent expression. As a consequence, both hybrids expressed more genes than did either parental inbred. SPE was not only detected in whole primary roots, but also in distinct tissues of this organ and each tissue expressed a specific set of genes with the SPE pattern. Only a minor part of the SPE genes identified from these analyses belong to one of the subgenomes implying that most of them emerged recently. The ability to compensate for alleles not expressed in one of the two parents might be a mechanism contributing to hybrid vigor.
