Zea mays Transcriptome or Gene expression. Zea mays

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. Keywords: genotype comparison Overall design: Gene expression levels were profiled in 19 day after pollination endosperm tissue from four maize genotypes; B73, Mo17, Mo17xB73 and B73xMo17.

植物胚乳（endosperm）的核基因组组成由两个母本基因组与一个父本基因组共同贡献而来，这种2:1的剂量比例关系为研究互交杂种（reciprocal hybrids）中基因表达水平的加性效应提供了独特的实验体系。本研究采用芯片表达谱分析与等位基因特异性表达（allele-specific expression）分析相结合的方法，以授粉后13天和19天两个发育阶段的玉米自交系B73、Mo17及其互交杂种的胚乳组织提取的RNA为材料开展实验。通过评估互交杂种中的相对表达水平，可确定加性与非加性表达模式的发生频率。尽管胚乳中多数差异表达基因呈现加性表达模式，但约10%的基因呈现非加性表达模式，包括母本样、父本样、显性高亲本、显性低亲本以及超出自交系表达范围的表达模式。玉米胚乳组织中超出亲本表达范围的杂种表达模式发生频率，远高于营养组织（vegetative tissues）中的观测结果。针对90个基因的集合，本研究采用等位基因特异性表达检测来监测等位基因偏向性（allelic bias）与调控变异（regulatory variation）。其中8个基因在胚乳发育的多个阶段呈现母本或父本偏向性表达的证据，属于潜在的差异基因印记（imprinting）调控实例。综合来看，本研究数据表明，亲本对基因表达的影响在胚乳中远强于营养组织，且胚乳中的基因印记现象可能比此前预估的更为普遍。关键词：基因型比较（genotype comparison） 整体实验设计：本研究对授粉后19天的四种玉米基因型（B73、Mo17、Mo17×B73及B73×Mo17）的胚乳组织进行了基因表达谱分析。