Abstract
BackgroundThe genus Brassica mainly comprises three diploid and three recently derived allotetraploid species, most of which are highly important vegetable, oil or ornamental crops cultivated worldwide. Despite being extensively studied, the origination of B. napus and certain detailed interspecific relationships within Brassica genus remains undetermined and somewhere confused. In the current high-throughput sequencing era, a systemic comparative genomic study based on a large population is necessary and would be crucial to resolve these questions.ResultsThe chloroplast DNA and mitochondrial DNA were synchronously resequenced in a selected set of Brassica materials, which contain 72 accessions and maximally integrated the known Brassica species. The Brassica genomewide cpDNA and mtDNA variations have been identified. Detailed phylogenetic relationships inside and around Brassica genus have been delineated by the cpDNA- and mtDNA- variation derived phylogenies. Different from B. juncea and B. carinata, the natural B. napus contains three major cytoplasmic haplotypes: the cam-type which directly inherited from B. rapa, polima-type which is close to cam-type as a sister, and the mysterious but predominant nap-type. Certain sparse C-genome wild species might have primarily contributed the nap-type cytoplasm and the corresponding C subgenome to B. napus, implied by their con-clustering in both phylogenies. The strictly concurrent inheritance of mtDNA and cpDNA were dramatically disturbed in the B. napus cytoplasmic male sterile lines (e.g., mori and nsa). The genera Raphanus, Sinapis, Eruca, Moricandia show a strong parallel evolutional relationships with Brassica.ConclusionsThe overall variation data and elaborated phylogenetic relationships provide further insights into genetic understanding of Brassica, which can substantially facilitate the development of novel Brassica germplasms.
Highlights
The genus Brassica mainly comprises three diploid and three recently derived allotetraploid species, most of which are highly important vegetable, oil or ornamental crops cultivated worldwide
Sequencing of the diverse cytoplasmic Brassica DNA haplotypes To distinguish the cytoplasmic DNA haplotypes within Brassica genus, genotyping analysis through High Resolution Melting (HRM) method were performed in our germplasm collections (Figure S1)
Two major chloroplast DNA (cpDNA) haplotypes were identified in 180 B. rapa accessions, while 180 B. juncea accessions contain one major cpDNA haplotype
Summary
The genus Brassica mainly comprises three diploid and three recently derived allotetraploid species, most of which are highly important vegetable, oil or ornamental crops cultivated worldwide. B. napus is supposed to originate from certain kind of hybridization between B. rapa and B. oleracea, which co-existed in European Mediterranean coastwise regions, at approximately 10,000 years ago [4]. It has diffused worldwide (mainly to Asia, America and Australia), and eventually formed several ecological and morphological types, which mainly include winter, spring and semi-winter ecotypes or oil-use, roottuberous and leafy morphotypes. The A and C subgenomes evolved asymmetrically and higher genetic diversity was identified in A subgenome [9]
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