Genomic insights into sex determination evolution in yam, an important staple food crop

Reductions in the cost of next generation sequencing and expertise required for whole genome assembly and annotation permits improvement of existing assemblies of industrially important models (Chinese hamster ovary cell line - CHO) and sequencing neglected agronomically important species, such as yam. Applying these new technologies, we have produced an improved reference for the CHO lineage, CHO-K1, and generated draft assemblies and annotations for three yam species. Yam is an important staple crop of great cultural and socioeconomic significance to Africa, the Americas, the Caribbean, South Pacific and Asia. I explored the evolutionary history of sex determination in dioecious Dioscorea species, a rare trait found in only 5-6% of angiosperms. We identified the most socio-economically important species, guinea yam (D. rotundata) to be female heterogametic (ZW), and confirmed the related basal species, oni-dokoro (D. tokoro), to be male heterogametic (XY). It is exciting to observe both ZW and XY sex determination systems in Dioscorea, as this indicates turnover of sex determination systems. There has been little study to date comparing plant species in the same genus with different sex determination systems, making Dioscorea a unique opportunity to investigate the turnover of sex determination. Through comparison of these two species, and generation of a draft reference for D. alata, I have begun to elucidate the ancestral state of sex within the genus. Generation of these genomic resources in yam and study of the evolution of sex determination, will assist with breeding programmes that will improve this important staple food crop. Finally, these findings will assist with future studies that aim to improve our fundamental understanding of the mechanisms of recombination and speciation in plants