On the origin of photoperiod non-responsiveness in barley

In barley, the transition from the vegetative to reproductive phase is complex and under the control of photoperiodic and temperature conditions. One major gene involved is , a () that encodes a component of the circadian clock. Mutation at resulted in the photoperiod non-responsive alleles that are beneficial under high latitudinal environments as they allow vegetative growth during the long-day summer conditions whereby higher yields are harvested by farmers. Utilizing a diverse GWAS panel of world-wide origin and a genome-wide gene-based set of 50K SNP markers, a strong association of days to heading with the gene was detected in multi-location field trials. Re-sequencing of the gene spanning putative causative SNPs, SNP22 () and SNP48 (), detected recombination between the two, previously reported to be in complete LD. Phenotyping of the recombinants and phylogenetic relationships among haplotypes supported the original conclusion of that SNP22, present in the CCT domain, is the most likely causative SNP. To infer the origin of non-responsiveness, the gene was re-sequenced in a geo-referenced collection of 2057 wild and domesticated barleys and compared with the allelic status of the 6000-year-old barley sample from the Yoram cave in the Masada cliff. A monophyletic and post-domestication origin in the Fertile Crescent was found in contrast to the pre-domestication origin proposed by . We show that the photoperiod non-responsiveness originated from Desert type wild barley in the Southern Levant.