The aim of this thesis is to investigate the evolution of cultivated flax (Linum usitatissimum L.). Specifically, it focuses on the adaptation of flax to European latitudes during the spread of agriculture. The two main objectives of this study are to determine 1) the role of hybridization with the flax wild relative (pale flax; Linum bienne Mill.) in the adaptation to northerly latitudes and 2) the link between the adaptation and the emergence of fibre flax varieties. Flowering time genes play an important role in adaptation to northerly latitudes. Homologs of three flowering genes from Arabidopsis thaliana (LFY, TFL1 and TOC1) were identified and sequenced in flax. This included seven flax paralogs of TFL1, which shared gene structure, exonic sequences, conservation of amino acids in the active site, and expression patterns with the phosphatidylethanolamine binding protein family that includes TFL1. Sixteen different haplotypes of LuTFL1 were discovered amongst sequence data derived from a diversity collection of flax accessions. Haplotypes in cluster I are associated with samples from Southern Europe and the Near East, while those in cluster III are associated with Central and Northern Europe. The LuTFL1 gene was under selection or selective sweep that occurred in cultivated flax. Haplotype I was inherited from pale flax during domestication, while haplotype III was inherited post-domestication following hybridization with pale flax from around the Bosphorus. Within sequence data of LuTFL2, ten haplotypes were discovered and these too were correlated with latitude. Contrary to the previous case however, there is no evidence of selection in LuTFL2. LuTFL1 and LuTFL2 might be in linkage disequilibrium. A collection of RADseq markers was developed to investigate the genetic structure of flax and measure the genetic migration between wild and cultivated species. Of all the RADseq markers, 219 were characterized with single SNP and used for further analyses. The genetic diversity of cultivated flax was found to be similar to that of pale flax. The population structure inferred from SNP data showed genetic separation of dehiscent and non-dehiscent varieties, but no distinction between intermediate, fibre and oil varieties of cultivated flax. The population is structured from south to north within landraces, intermediate and fibre varieties. There is strong evidence for admixture from pale flax to cultivated flax, especially from the populations in the area of domestication. High levels of genetic migration are shown from all populations of pale flax towards both the southern and northern cultivated flax. RADseq SNP alleles that are associated with northerly latitudes in cultivated flax were introduced through post-domestication hybridization with pale flax of various geographic origin. These combined molecular results indicate that pale flax contributed to the adaptation of cultivated flax in the European climate through post-domestication gene flow. Considering archaeological and phenotypic data from the literature, the adaptation to northerly latitude might have led to the emergence of fibre varieties. This inference is supported by a custom-made programme called PGROWTH, which models the impact of FT and TFL1 gene expression on flax architecture. These two genes play an important role in plant development and therefore might have an impact on flax architecture. This study suggests the need of carrying out transgenic, functional experiments with LuTFL1 constructs in the future.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:640957 |
| Date | January 2014 |
| Creators | Gutaker, Rafał M. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/66545/ |
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