An updated explanation of ancestral karyotype changes and reconstruction of evolutionary trajectories to form Camelina s
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RESEARCH ARTICLE
Open Access
An updated explanation of ancestral karyotype changes and reconstruction of evolutionary trajectories to form Camelina sativa chromosomes Zhikang Zhang1†, Fanbo Meng1†, Pengchuan Sun1, Jiaqing Yuan2, Ke Gong1, Chao Liu1, Weijie Wang1* and Xiyin Wang1,3*
Abstract Background: Belonging to lineage I of Brassicaceae, Camelina sativa is formed by two hybridizations of three species (three sub-genomes). The three sub-genomes were diverged from a common ancestor, likely derived from lineage I (Ancestral Crucifer karyotype, ACK). The karyotype evolutionary trajectories of the C. sativa chromosomes are currently unknown. Here, we managed to adopt a telomere-centric theory proposed previously to explain the karyotype evolution in C. sativa. Results: By characterizing the homology between A. lyrata and C. sativa chromosomes, we inferred ancestral diploid karyotype of C. sativa (ADK), including 7 ancestral chromosomes, and reconstructed the evolutionary trajectories leading to the formation of extant C. sativa genome. The process involved 2 chromosome fusions. We found that sub-genomes Cs-G1 and Cs-G2 may share a closer common ancestor than Cs-G3. Together with other lines of evidence from Arabidopsis, we propose that the Brassicaceae plants, even the eudicots, follow a chromosome fusion mechanism favoring end-end joining of different chromosomes, rather than a mechanism favoring the formation circular chromosomes and nested chromosome fusion preferred by the monocots. Conclusions: The present work will contribute to understanding the formation of C. sativa chromosomes, providing insight into Brassicaceae karyotype evolution. Keywords: Brassicaceae, C. sativa, Chromosome, Karyotype, Polyploid
Background Brassicaceae (mustard family) is one of the largest groups in plants, being composed of an approximate 3709 species, classified into 338 genera [1]. It includes several species of prominent scientific and economic importance. According to phylogenetic relationship, Camelineae species (Arabidopsis thaliana, Arabidopsis lyrata, * Correspondence: [email protected]; [email protected] † Zhikang Zhang and Fanbo Meng contributed equally to this work. 1 School of Life Sciences, North China University of Science and Technology, Tangshan 063210, Hebei, China Full list of author information is available at the end of the article
and Capsella rubella) and Brassica species (Brassica rapa, Brassica nigra and Brassica oleracea) respectively represent lineage I and lineage II, two of three wellsupported lineages among the Brassicaceae [2, 3]. With the rapid increase of Brassicaceae genome assemblies, reconstructing ancestral genome can help understand the evolutionary history of the extant Brassicaceae families and species. With genetic maps of A. lyrata and C. rubella, Schranz et al. defined 24 conversed GBs (labelled as A-X) related to ancestral karyotype (AK, n = 8) [4]. Ancestral crucifer karyotype (ACK, n =
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