Cis -regulation of gene expression between sexes and life stages in Rumex hastatulus
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The potential for conflict between sexes and life stages while sharing predominantly the same genome has important evolutionary consequences. In dioecious flowering plants, genes beneficial for the haploid pollen stage may reduce the fitness of diploid offspring of both males and females. Such antagonistic pleiotropy between sexes and life stages can in some cases maintain genetic variation. However, we still lack understanding of the extent of shared genetic architecture for gene expression between the sexes or life stages in plants, a key component for predicting the scope for conflict. We performed expression quantitative trait loci (eQTL) mapping to test if standing variation affects sexes and life stages differently using a population sample of the dioecious outcrossing plant Rumex hastatulus . We compared effect sizes and allele frequencies of cis -eQTLs in male and female leaf tissues and pollen, and tested for genotype-by-sex interactions for gene expression. We found stronger shared genetic architecture between sexes than between the life stages. In addition, comparisons of the site frequency spectra for cis -eQTLs to a null distribution found no evidence for a genome-wide pattern consistent with purifying selection. Our results suggest that any conflict over optimal gene expression between pollen and leaves may be easily resolved due to their distinct genetic architectures, whereas there is more scope for conflict between the sexes in gene expression for leaves. Our study highlights the use of eQTL mapping to infer the scope of shared genetic architecture and for investigating the evolution of conflict between sexes and life stages in dioecious species.
Author Summary
Conflict may arise when different sexes or life stages have contrasting ‘evolutionary interests’. The degree of shared genetic basis between sexes or life stages in a phenotypic trait such as gene expression can indicate whether there is the scope for ongoing conflict. We identified cis-regulatory variation using expression quantitative loci (eQTL) mapping in leaf and pollen tissues of a dioecious plant, and tested the scope of conflict between sexes and life stages. We found more shared eQTLs and stronger positive correlation in their effects on expression between sexes than life stages, suggesting more shared genetic basis and higher potential for ongoing conflict between sexes than life stages. In addition, we tested selective pressures on cis-regulatory variation using allele frequencies and found similar patterns of selective pressures on eQTLs between sexes and life stages with an overabundance of rare alleles. By comparing to a null distribution, the excessive rare alleles in eQTLs did not suggest a genome-wide signal of purifying selection.
