Dosage effects on gene expression in a maize ploidy series.

Previous studies on gene expression in aneuploids revealed numerous trans-acting dosage effects. Segmental aneuploidy of each varied chromosomal region exhibited predominantly inverse effects on several target genes. Here, dosage regulation was examined in a maize (Zea mays L.) ploidy series where the complete genomic complement is varied. Total RNA from leaf tissue of monoploid, diploid, triploid, and tetraploid plants (1x, 2x, 3x, and 4x, respectively) was analyzed for the expression of 18 genes. For most tested genes, the transcript level per cell is directly proportional to structural gene dosage; that is, on a per genome basis, there is approximately equal expression among the four ploidies. Exceptional cases show a negative correlation of expression with ploidy or a positive correlation greater than expected from the structural gene dosage. These studies suggest that, in general, as structural gene dosage increases in multiples of the monoploid complement, the absolute level of gene expression per cell increases. In contrast, addition or subtraction of only a single chromosome arm tends to alter gene expression patterns extensively. The combined results of the euploid and aneuploid studies suggest that aneuploid effects result from an altered stoichiometry of the factors contributing to the mechanisms of gene expression.