Zea mays Transcriptome or Gene expression. Zea mays

Heterosis and polyploidy are two important aspects of plant evolution. To examine these issues, we conducted a global gene expression study of a maize ploidy series as well as a set of tetraploid inbred and hybrid lines. This gene expression analysis complements an earlier phenotypic study of these same materials. We find that ploidy change affects a large fraction of the genome, albeit at low levels; gene expression changes rarely exceed 2-fold and are typically not statistically significant. The most common gene expression profile we detected is greater than linear increase from monoploid to diploid, and reductions from diploid to triploid and from triploid to tetraploid, a trend that mirrors plant stature. When examining heterosis in tetraploid maize lines, we found a large fraction of the genome impacted but the majority of changes were not statistically significant at 2-fold or less. Non-additive expression was common in the hybrids, and the extent of non-additivity increased both in number and magnitude from duplex to quadruplex hybrids. Overall, we find that gene expression trends mirror observations from the phenotypic studies; however, obvious mechanistic connections remain unknown. Overall design: We examined gene expression in a ploidy series (1n to 4n) of the maize line B73 and in a variety of hybrid tetraploid lines using a complex loop design. Pooled RNA samples from 10 plants were used (2 independent RNA isolations/sample), and all comparisons were made using replicate dye swaps (16 slide sets/comparison). For the ploidy analysis, all expression changes were computed relative to the diploid as well as between 2n + 3n and 3n + 4n. For the expression analysis of hybrids, hybrid expression levels were compared to the parental expression levels as well as to mid-parent levels.