Abstract
BackgroundCastor 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.ResultsHere 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 ~ 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 ~ 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.ConclusionsThis 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.
Highlights
Castor bean (Ricinus communis L.) is an important oil crop, which belongs to the Euphorbiaceae family
97.4% (~ 328 Mb) of the genome was anchored onto 10 pseudochromosomes, which was further validated by a physical map we constructed in this study (Fig. 1a and Additional file 1: Fig. S3)
Our results clearly show that accessions from East Africa are the extant wild progenitors of castor bean and that domestication occurred somewhere between East Africa and West Asia, and these are the main centers of diversity
Summary
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 It remains largely unknown regarding the origin, domestication, and the genetic basis of key traits of castor bean. Prehistoric uses of castor bean have been revealed by archeological discovery in South Africa (dated to ~ 24,000 years before present, YBP) [7] and early management has been found in Sudan (~ 7000 YBP) [8], Egypt (~ 4000 YBP) [9], and Iraq (~ 6000 YBP) [10] These anthropological records highlight how non-food plants have been widely used by humans since prehistoric times. A few studies investigating the genetic diversity of castor bean have included a few wild accessions collected from East Africa concluding that wild germplasm does harbor higher genetic diversity [16, 17], the population demographic history of wild castor bean, genetic bottlenecks, selection signatures during domestication, and the genetic basis of key agronomic traits remain largely unexplored
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