Conservation of imprinted expression across genotypes is correlated with consistency of imprinting across endosperm development in maize.

Abstract

Imprinted expression is an essential process for seed viability affecting hundreds of genes in Zea mays endosperm, however most studies have examined just one time point for analysis. The focus on single time points can limit our ability to identify imprinted genes, and our ability to draw conclusions for the role of imprinting in endosperm. In this study we examine imprinted expression across four time points ranging from the transition to endoreduplication from mitotic division through the beginning of programmed cell death. Additionally, we assessed imprinting variation across eight diverse maize lines, six of which have never before been assessed for imprinting. Through this analysis we identify over 700 imprinted genes with varying consistency across time points including 255 genes imprinted at every time point and 105 genes displaying transient imprinting. We find a correlation between high consistency of imprinting across time and high conservation of parental bias across eight diverse maize lines reciprocally crossed with B73. Additionally, we identify evidence of imprinting for three zein genes that are critical for nutrient accumulation in the endosperm, suggesting that imprinting may play a more important role in seed composition than previously thought. Taken together, this study provides a more holistic view of imprinting variation across time and across genotypes in maize and enables us to more thoroughly investigate the complex imprinting landscape.