The impact of photoperiod insensitive Ppd‐1a mutations on the photoperiod pathway across the three genomes of hexaploid wheat ( Triticum aestivum )

Summary Flowering time is a trait that has been extensively altered during wheat domestication, enabling it to be highly productive in diverse environments and providing a rich source of variation for studying adaptation mechanisms. Hexaploid wheat is ancestrally a long‐day plant, but many environments require varieties with photoperiod insensitivity (PI) that can flower in short days. PI results from mutations in the Ppd‐1 gene on the A, B or D genomes, with individual mutations conferring different degrees of earliness. The basis of this is poorly understood. Using a common genetic background, the effects of A, B and D genome PI mutations on genes of the circadian clock and photoperiod pathway were studied using genome‐specific expression assays. Ppd‐1 PI mutations did not affect the clock or immediate clock outputs, but affected TaCO1 and TaFT1 , with a reduction in TaCO1 expression as TaFT1 expression increased. Therefore, although Ppd‐1 is related to PRR genes of the Arabidopsis circadian clock, Ppd‐1 affects flowering by an alternative route, most likely by upregulating TaFT1 with a feedback effect that reduces TaCO1 expression. Individual genes in the circadian clock and photoperiod pathway were predominantly expressed from one genome, and there was no genome specificity in Ppd‐1 action. Lines combining PI mutations on two or three genomes had enhanced earliness with higher levels, but not earlier induction, of TaFT1 , showing that there is a direct quantitative relationship between Ppd‐1 mutations, TaFT1 expression and flowering.