Unknown,Transcriptomics,Genomics,Proteomics

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Gene expression analysis at the intersection of ploidy and hybridity in maize.

ABSTRACT: 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. 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.

ORGANISM(S): Zea mays

SUBMITTER: Nicole Riddle

PROVIDER: E-GEOD-25526 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:The nuclear content of the plant endosperm is the result of the contribution two maternal genomes and a single paternal genome. This 2:1 dosage relationship provides a unique system for studying the additivity of gene expression levels in reciprocal hybrids. A combination of microarray profiling and allele-specific expression analysis was performed using RNA isolated from endosperm tissues of maize inbred lines B73 and Mo17 and their reciprocal hybrids at two developmental stages, 13 and 19 days after pollination. By assessing the relative levels of expression in the reciprocal hybrids it was possible to determine the prevalence of additive and non-additive expression patterns. While the majority of differentially expressed genes displayed additive expression patterns in the endosperm, approximately 10% of the genes displayed non-additive expression patterns including maternal-like, paternal-like, dominant high-parent, dominant low-parent and expression patterns outside the range of the inbreds. The frequency of hybrid expression patterns outside of the parental range in maize endosperm tissue is much higher than that observed for vegetative tissues. For a set of 90 genes allele-specific expression assays were employed to monitor allelic bias and regulatory variation. Eight of these genes exhibited evidence for maternally or paternally biased expression at multiple stages of endosperm development and are potential examples of differential imprinting. Collectively, our data indicate that parental effects on gene expression are much stronger in endosperm than in vegetative tissues, and that endosperm imprinting may be far more common than previously estimated. Experiment Overall Design: Affymetrix microarrays were used to perform expression profiling on 13 day after pollination endosperm tissue of four different genotypes; B73; Mo17, B73xMo17 and Mo17xB73. There are three biological replicates for each of the tissues. Each biological sample represents a pool containing 5 endosperms each, from 6 different ears.