Comparison of maize (Zea mays L.) F₂-hybrid and parental inbred line primary root transcriptomes suggests organ specific patterns of non-additive gene expression and conserved expression trends between different hybrids in a subset of genes

The phenomenon of heterosis describes the increased agronomic performance of heterozygous F1-plants compared to their homozygous parental inbred plants. Heterosis is manifested during the early stages of root development in maize. The goal of this study was to identify non-additive gene expression in primary roots of maize hybrids compared to the average expression levels of their parental inbred lines. To achieve this goal a two step strategy was selected. First, a microarray preselection of non-additively expressed candidate genes was performed. Subsequently, gene expression levels in a subset of genes were determined via high throughput qRT-PCR experiments. Initial microarray experiments identified 1941 distinct microarray features which displayed non-additive gene expression in at least one of the twelve analyzed hybrids compared to the midparent value of their parental inbred lines. Most non-additively expressed genes were expressed between the parental values (> 89%). Comparison of these 1941 genes with non-additively expressed genes identified in maize shoot apical meristems via the same experimental procedure in the same genotypes revealed significantly less overlap than expected by pure chance. This finding suggests organ specific patterns of non-additively expressed genes at least between the compared organs. qRT-PCR analyses of 64 of the 1941 genes in four different hybrids revealed conserved patterns of non-additively expressed gene expression in different hybrids. Subsequently, 22 of the 64 genes that displayed non-additive expression in all four hybrids were analyzed in twelve hybrids that were generated from four inbred lines. Among those genes a superoxide dismutase 2 was expressed significantly above the midparent value in all twelve hybrids and might thus play a protective role in antioxidative defense in the primary root of maize hybrids. The findings of this study are consistent with the hypothesis that global expression trends but also the consistent differential expression of key genes might be relevant during the organ-specific manifestation of heterosis.

Key Words: expression profiling, heterosis, maize, primary root, superoxide dismutase

Online ISS 1091-6490
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