Pollen and anther morphological variation in rye was shaped by domestication

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.

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.

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.