In a recent study, now published in Molecular Biology and Evolution, we have found evidence of strong maternal effects on gene expression in Arabidopsis lyrata hybrids (Videvall et al. 2015).
Hybridization between populations or species can have pronounced fitness consequences. Yet little is known about how hybridization affects gene regulation. Three main models have been put forward to explain gene expression patterns in hybrids: additive, dominance or parental effects. Here we use high throughput RNA-sequencing to examine the extent to which hybrid gene expression follows predictions by each of the three models. We performed a reciprocal crossing experiment between two differentiated populations of the perennial herb Arabidopsis lyrata and sequenced RNA in rosette leaves of twelve-week-old plants grown in greenhouse conditions. The two parental populations had highly differentiated gene expression patterns. In hybrids, a majority of genes showed intermediate expression relative to that of their parental populations (i.e. additive effects), but expression was frequently more similar to the maternal than to their paternal population (i.e. maternal effects). Allele-specific expression analyses showed that in the vast majority of cases, genes with pronounced maternal effect expressed both the maternal and the paternal allele. Maternal effects on hybrid gene expression have rarely been documented previously and our study suggests it could be more common than previously assumed. Whether the maternal effect on gene expression persists to later life-stages, and whether the variation in gene expression is manifested in other aspects of the phenotype, remain to be elucidated. Our findings are relevant for understanding the consequences of outbreeding and hybridization and open up several questions for future studies.
Gene expression pattern in hybrids at genes that were significantly differentially expressed between populations. Expression levels of genes (log10 normalized counts) that were significantly differentially expressed between populations (“SW high”: genes more highly expressed in Sweden (n = 8355); “NW high”: genes more highly expressed in Norway (n = 1218)) in (A) hybrids with Norwegian mother compared to hybrids with Swedish mother, (B) in hybrids with Norwegian mother compared to the Norwegian population, and (C) hybrids with Swedish mother compared to the Swedish population.