Adaptation to European latitudes through assimilation of wild diversity at the LuTFL1 locus altered architecture and promoted fiber production in flax.

After domestication in the Near East around 10,000 years ago several founder crops spread and adapted to European latitudes. On reaching northerly latitudes the architecture of domesticated flax changed becoming more suitable to fiber production over oil, with longer stems, smaller seeds and fewer axillary branches. Latitudinal adaptations in crops typically result in changes in flowering time, often involving the PEBP family of genes that also have the potential to influence plant architecture. We identify PEBP family genes in the flax genome, describe molecular diversity of two loci, LuTFL1 and LuTFL2 in wild and cultivated flax that vary over latitudinal range, and show that cultivated flax received LuTFL1 alleles from more northerly wild flax populations. Compared to a genomic background of population structure of flaxes over latitude determined using restriction site-associated loci, the LuTFL1 alleles display a level of differentiation that is consistent with selection both for a northern associated allele (III) and against a southern associated allele (I) in the north. We also demonstrate that LuTFL1 alleles are associated with differing flowering time, and through heterologous expression in Arabidopsis thaliana that LuTFL1 is a functional homolog of TFL1 in Arabidopsis thaliana and is capable of changing both flowering time and plant architecture. We conclude that specialized fiber flax types formed as a consequence of a natural adaptation of cultivated flax to higher latitudes.