Stupar et al. studied the gene expression profiles between maize F1 hybrids and their parents, and approximately 75% of the differentially expressed genes showed additive expression patterns between F1 hybrids and parents [ 13].
In contrast, the study by Chagué et al. [ 44] documented that the great majority (ca. 93%) of 30,000 transcripts analyzed showed additive expression and, hence, leaving only about 7% of genes as non-additively expressed in two synthetic lines.
Several studies have found that the majority (~75%) of genes exhibit additive expression in the hybrid and that only small numbers of the non-additively expressed genes exhibit expression levels outside the parental range [ 11, 15, 17].
The low level and stochastic nature of non-additive expression of differentially expressed genes results in an overall proportion of additive expression of 83.1% (with 16.9% non-additive) for MPH-correlated genes, and a slightly smaller contingent of 74.2% (with 25.8% non-additive) for those non-correlated genes.
The majority of differentially expressed genes in each of the six different hybrids exhibited additive expression patterns, and ~25% exhibited statistically significant non-additive expression profiles.
Overall, most genes generally showed additive expression.
Thus, results from these two related polyploid species suggest that many changes in gene expression within independently resynthesized lines were random, and many genes show additive expression.
This illustrated how the double mutant displays a combined, additive expression profile of both single mutants and one would therefore expect to see an additive phenotype.
This leads to the prediction that genes showing the observed additive expression responses to copy number variation belong to these two categories.
At5g26130) showed the greatest deviation from additive expression levels among the allopolyploid lines by quantitative RT-PCR (Figure 4A), and expression exceeded high-parent (TO1000) levels by ≥2 fold in all lines (not shown).
In general, the hybrids exhibited additive expression and the majority of genes with non-additive expression still exhibited expression levels within the parental range.
