Pollen and anther morphological variation in rye was shaped by domestication.

Background: In plants and animals, pollen or sperm morphology differ greatly between species. Across plant species, pollen morphological diversity is broadly linked to different pollination systems. However, the extent of within-species diversity is less well understood. To address this question, we explored pollen and anther diversity in rye (Secale cereale L.), a wind-pollinating grass species.

Results: We analysed 339 domesticated, feral and wild rye individuals of 64 diverse accessions. Population structure analysis revealed a differentiation gradient from wild to domesticated rye. We found pronounced within-species diversity of pollen and anther morphology. Genome-wide association scans uncovered a polygenic architecture of pollen and anther traits, with medium to high heritability and mostly small-effect loci. A subset of these loci overlapped with previously identified domestication loci, for which the underlying traits were unknown. A P_ST-F_ST analysis suggests that pollen and anther traits were under selection throughout rye domestication. Population genomic analyses revealed signatures of selection at 37% of all identified loci.

Conclusion: Our work shows that selection for larger pollen grains and longer anthers occurred throughout rye domestication. The present study extends our knowledge of the genetic architecture underlying within-species pollen and anther morphological diversity, and further unravels domestication traits in rye.