RT Journal Article SR Electronic T1 Pollen-specific genes accumulate more deleterious mutations than sporophytic genes under relaxed purifying selection in Arabidopsis thaliana. JF bioRxiv FD Cold Spring Harbor Laboratory SP 016626 DO 10.1101/016626 A1 MC Harrison A1 EB Mallon A1 D Twell A1 RL Hammond YR 2015 UL http://biorxiv.org/content/early/2015/03/17/016626.abstract AB The strength of purifying selection varies among loci and leads to differing frequencies of deleterious alleles within genomes. Selection is generally stronger for highly and broadly expressed genes but can be less efficient for diploid expressed, deleterious alleles if heterozygous. In plants expression level, tissue specificity and ploidy level differ between pollen specific and sporophyte specific genes. This may explain why the reported strength and direction of the relationship between selection and the specificity of a gene to either pollen or sporophytic tissues varies between studies and species. In this study, we investigate the individual effects of expression level and tissue specificity on selection efficacy within pollen genes and sporophytic genes of Arabidopsis thaliana. Due to high homozygosity levels caused by selfing, masking is expected to play a lesser role. We find that expression level and tissue specificity independently influence selection in A. thaliana. Furthermore, contrary to expectations, pollen genes are evolving faster due to relaxed purifying selection and have accumulated a higher frequency of deleterious alleles. This suggests that high homozygosity levels resulting from high selfing rates reduce the effects of pollen competition and masking in A. thaliana, so that the high tissue specificity and expression noise of pollen genes are leading to lower selection efficacy compared to sporophyte genes.