Identification and molecular characterization of novel Rht-1 alleles in hard red spring wheat

The introduction of the semidwarfing alleles, Rht-B1b and Rht-D1b, into wheat (Triticum aestivum L.) varieties significantly increased wheat yields beginning in the 1960s. Despite their agronomic advantage, Rht-B1b and Rht-D1b are also associated with decreased grain protein content and decreased coleoptile length. Furthermore, there is limited allelic diversity available to wheat breeders beyond Rht-B1b and Rht-D1b. We identified 16 ethyl methanesulfonate (EMS)-induced Rht-1 alleles, including a nonsense mutation in each Rht-1 gene: Rht-A-Q555stop, Rht-B-Q420stop, and Rht-D-W559stop. We focused our attention for this study on stop alleles since the Rht-B1b and Rht-D1b alleles also contain premature stop codons. We evaluated the new nonsense alleles by measuring their impact on coleoptile length, gibberellic acid (GA) sensitivity, and DELLA/GID1 interaction. Rht-A-Q555stop reduced coleoptile length 16% compared with Rht-1a (wild type) and repressed coleoptile GA perception similarly to Rht-B1b and Rht-D1b. Rht-B-Q420stop and Rht-D-W559stop did not affect coleoptile length. However, Rht-B-Q420stop reduced the ability of germinating seeds to perceive GA, but not as much as Rht-A555stop, Rht-B1b, or Rht-D1b. We also tested whether the novel mutations affected the interaction between DELLA/GID1 in the presence and absence of GA. We found that Rht-A-Q555stop, Rht-B-Q420stop, and Rht-D-W559stop inhibited DELLA/GID1 interaction in the absence of GA, but the interaction was restored in the presence of GA. The identification of Rht-A-Q555stop, Rht-B-Q420stop, and Rht-D-W559stop increases the allelic diversity of Rht-1. This study also indicates that the RHT carboxyl terminus is important for DELLA/GID1 interactions.

Automated summary

The introduction of semidwarfing alleles Rht-B1b and Rht-D1b significantly increased wheat yields, but may lead to issues such as decreased grain protein content. In addition, there is limited allelic diversity available to wheat breeders beyond Rht-B1b and Rht-D1b.