Deleterious mutation accumulation in Arabidopsis thaliana pollen genes: a role for a recent relaxation of selection

As with reproductive genes generally, we expect a faster evolution of plant pollen genes compared to sporophytic genes. Haploid expression in pollen leads to advantageous and deleterious alleles not being masked by a dominant homologue. A combination of haploid expression and pollen competition have been suggested as being responsible for stronger purifying and positive selection on pollen genes. However, it is unlikely that this mechanism is so straightforward in the model plant species Arabidopsis thaliana . Since becoming self-compatible roughly 1 MYA high selfing rates have caused high homozygosity levels which in turn can be expected to reduce pollen competition and the effect of masking in diploid expressed, sporophytic genes. In this study we investigated the relative strength of selection on pollen genes compared to sporophytic genes in A. thaliana . We were especially interested in comparing ancestral selection patterns when A. thaliana was an obligate outcrosser with more recent selection patterns since the plant's loss of self-incompatibility. We present two major findings: 1) before becoming self-compatible both positive and purifying selection was stronger on pollen genes than sporophytic genes for A. thaliana ; 2)...Continue Reading