DOSAGE EFFECTS ON GENE-EXPRESSION IN A MAIZE PLOIDY SERIES

Previous studies on gene expression in aneuploids revealed numerous tr ans-acting dosage effects. Segmental aneuploidy of each varied chromos omal region exhibited predominantly in inverse effects on several targ et genes. Here, dosage regulation was examined in a maize (Zea mays L. ) ploidy series where the complete genomic complement is varied. Total RNA fr om leaf tissue of monoploid, diploid, triploid, and tetraploid plants (1x, 2x, 3x, and 4x, respectively) was analyzed for the expres sion 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 s tructural gene dosage. These studies suggest that, in general, as stru ctural 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 alt er gene expression patterns extensively. The combined results of the e uploid and aneuploid studies suggest that aneuploid effects result fro m an altered stoichiometry of the factors contributing to the mechanis ms of gene expression.