Abstract
BackgroundDeciphering the genetic structure of Arabidopsis thaliana diversity across its geographic range provides the bases for elucidating the demographic history of this model plant. Despite the unique A. thaliana genomic resources currently available, its history in North Africa, the extreme southern limit in the biodiversity hotspot of the Mediterranean Basin, remains virtually unknown.ResultsTo approach A. thaliana evolutionary history in North Africa, we have analysed the genetic diversity and structure of 151 individuals collected from 20 populations distributed across Morocco. Genotyping of 249 genome-wide SNPs indicated that Morocco contains substantially lower diversity than most analyzed world regions. However, IBD, STRUCTURE and PCA clustering analyses showed that genetic variation is strongly geographically structured. We also determined the genetic relationships between Morocco and the closest European region, the Iberian Peninsula, by analyses of 201 populations from both regions genotyped with the same SNPs. These analyses detected four genetic groups, but all Moroccan accessions belonged to a common Iberian/Moroccan cluster that appeared highly differentiated from the remaining groups. Thus, we identified a genetic lineage with an isolated demographic history in the south-western Mediterranean region. The existence of this lineage was further supported by the study of several flowering genes and traits, which also found Moroccan accessions similar to the same Iberian group. Nevertheless, genetic diversity for neutral SNPs and flowering genes was higher in Moroccan than in Iberian populations of this lineage. Furthermore, we analyzed the genetic relationships between Morocco and other world regions by joint analyses of a worldwide collection of 337 accessions, which detected an additional weak relationship between North Africa and Asia.ConclusionsThe patterns of genetic diversity and structure of A. thaliana in Morocco show that North Africa is part of the species native range and support the occurrence of a glacial refugium in the Atlas Mountains. In addition, the identification of a genetic lineage specific of Morocco and the Iberian Peninsula indicates that the Strait of Gibraltar has been an A. thaliana migration route between Europe and Africa. Finally, the genetic relationship between Morocco and Asia suggests another migration route connecting north-western Africa and Asia.
Highlights
Deciphering the genetic structure of Arabidopsis thaliana diversity across its geographic range provides the bases for elucidating the demographic history of this model plant
The largest diversity has been found in the Iberian Peninsula, whose strong geographic structure has prompted the hypothesis of multiple Iberian glacial refugia with differential contribution to the colonization of Europe [16]
Genetic diversity and structure in North Africa To determine the genetic diversity of A. thaliana in North Africa we sampled 151 individuals in 20 populations distributed across the major mountain ranges of Morocco (Figure 1A, Additional file 1: Figure S1, Additional file 2: Table S1)
Summary
Deciphering the genetic structure of Arabidopsis thaliana diversity across its geographic range provides the bases for elucidating the demographic history of this model plant. Deciphering the genetic structure of A. thaliana diversity across its geographic range is a major aim because it explains its current ecological distribution, it reflects its demographic history, and it enables the precise design and analysis of experimental populations used to determine the molecular mechanisms of adaptive traits [6,7,8]. A glacial refugium in the Iberian Peninsula has been proposed to contribute to a west–east colonization of western and northern Europe, while an Asian refugium was likely the source for an east–west colonization of eastern and northern Europe In agreement with this view, genetic structure analyses of northern European populations have detected several differentiated clusters, which support multiple sources of postglacial colonization [18,19,20]. Genetic studies of North American and Japanese populations have detected no or weak geographic patterns, which indicate a very recent colonization from multiple sources [13,23,24]
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