Genomic insights into the origin, domestication and genetic basis of agronomic traits of castor bean

Background: Castor bean (Ricinus communis L.) is an important oil crop, which belongs to the Euphorbiaceae family. The seed oil of castor bean is currently the only commercial source of ricinoleic acid that can be used for producing about 2000 industrial products. However, it remains largely unknown regarding the origin, domestication, and the genetic basis of key traits of castor bean. Results: Here we perform a de novo chromosome-level genome assembly of the wild progenitor of castor bean. By resequencing and analyzing 505 worldwide accessions, we reveal that the accessions from East Africa are the extant wild progenitors of castor bean, and the domestication occurs similar to 3200 years ago. We demonstrate that significant genetic differentiation between wild populations in Kenya and Ethiopia is associated with past climate fluctuation in the Turkana depression similar to 7000 years ago. This dramatic change in climate may have caused the genetic bottleneck in wild castor bean populations. By a genome-wide association study, combined with quantitative trait locus analysis, we identify important candidate genes associated with plant architecture and seed size. Conclusions: This study provides novel insights of domestication and genome evolution of castor bean, which facilitates genomics-based breeding of this important oilseed crop and potentially other tree-like crops in future.

Automated summary

This study sheds light on the domestication and genome evolution of castor bean by performing de novo chromosome-level genome assembly of its wild progenitor and analyzing worldwide accessions. Important candidate genes associated with plant architecture and seed size were identified through genome-wide association study and quantitative trait locus analysis. This provides valuable insights for genomics-based breeding of castor bean and potentially other tree-like crops in the future.