Abstract
SummarySesame (Sesamum indicum L.) is an important oil crop renowned for its high oil content and quality. Recently, genome assemblies for five sesame varieties including two landraces (S. indicum cv. Baizhima and Mishuozhima) and three modern cultivars (S. indicum var. Zhongzhi13, Yuzhi11 and Swetha), have become available providing a rich resource for comparative genomic analyses and gene discovery. Here, we employed a reference‐assisted assembly approach to improve the draft assemblies of four of the sesame varieties. We then constructed a sesame pan‐genome of 554.05 Mb. The pan‐genome contained 26 472 orthologous gene clusters; 15 409 (58.21%) of them were core (present across all five sesame genomes), whereas the remaining 41.79% (11 063) clusters and the 15 890 variety‐specific genes were dispensable. Comparisons between varieties suggest that modern cultivars from China and India display significant genomic variation. The gene families unique to the sesame modern cultivars contain genes mainly related to yield and quality, while those unique to the landraces contain genes involved in environmental adaptation. Comparative evolutionary analysis indicates that several genes involved in plant‐pathogen interaction and lipid metabolism are under positive selection, which may be associated with sesame environmental adaption and selection for high seed oil content. This study of the sesame pan‐genome provides insights into the evolution and genomic characteristics of this important oilseed and constitutes a resource for further sesame crop improvement.
Highlights
Sesame has been cultivated for more than 5000 years, but has been mostly restricted to the developing and emerging countries (Anastasi et al, 2017)
Our results suggest that sesame landraces (Baizhima and Mishuozhima) and sesame modern cultivars (Zhongzhi13 and Yuzhi11) in China diverged ~4.7 million years ago (MYA), while modern Chinese sesame cultivars (Zhongzhi13 and Yuzhi11) were estimated to have diverged ~0.9 MYA, which is consistent with the breeding history of these two modern cultivars originating from neighbouring provinces (Hubei and Henan provinces) in China
The analysis suggests that the Indian modern cultivar Swetha was domesticated earlier than Chinese modern cultivars, which is consistent with the previous reports that sesame was firstly domesticated in the Indian subcontinent (Bedigian, 2003)
Summary
Sesame has been cultivated for more than 5000 years, but has been mostly restricted to the developing and emerging countries (Anastasi et al, 2017). Recent studies focused on the nutraceutical, pharmaceutical, cosmeceutical, industrial and ethnobotanical properties of bioactive components in sesame seeds, which renewed interest in this relatively under-explored crop plant (Anilakumar et al, 2010; Cheng et al, 2006; Dossa et al, 2017a; Kanu et al, 2007). Recent studies revealed variation in sesame seed composition (Dossa et al, 2017b; Pathak et al, 2014; Spandana et al, 2013; Wang et al, 2012a). In contrast to many other crop species, cultivated sesame varieties display a high degree of genetic diversity which can be utilized for crop improvement (Dossa et al, 2016; Uncu et al, 2015; Wang et al, 2014a; Wei et al, 2014; Zhang et al, 2012). The genetic and associated phenotypic variation of sesame may be a result of adaptation to diverse growth habitats (Bedigian and Harlan, 1986), as well as the artificial selection pressures resulting in its partially domesticated status (Wei et al, 2015)
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