Allelic variants in the PRR37 gene and the human-mediated dispersal and diversification of sorghum.
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Allele phylogenetic analysis of the sorghum flowering-time gene PRR37 provided new insight into the human-mediated selection of a key adaptive gene that occurred during sorghum's diversification and worldwide dispersal. The domestication and spread of the tropical cereal sorghum is associated with the historic movement of humans. We show that an allelic series at PRR37 (pseudo-response regulator 37), a circadian clock-associated transcription factor, was selected in long-day ecosystems worldwide to permit floral initiation and grain production. We identified a series of loss-of-function (photoperiod-insensitive) alleles encoding truncated PRR37 proteins, alleles with key amino acid substitutions in the pseudo-receiver domain, and a novel splice variant in which the pseudo-receiver domain is truncated. Each PRR37 allelic variant was traced to a specific geographic location or specialized agronomic type. We present a graphical model that shows evidence of human selection and gene flow of the PRR37 allelic variants during the global dispersal and agronomic diversification of sorghum. With the recent identification of the Ghd7 gene as an important regulator of flowering date in sorghum, we briefly examine whether loss-of-function Ghd7 allelic variants were selected prior to the human-mediated movement of sorghum from its equatorial center of origin to temperate climates worldwide.