N‐terminal Rht‐A1 mutations modify spring wheat ( Triticum aestivum L.) plant height

Abstract The Reduced Height‐1 ( Rht‐1 ) gene in wheat ( Triticum aestivum L.) has been well studied since the introgression of semidwarfing alleles Rht ‐ B1b and Rht ‐ D1b into many wheat varieties in the mid‐20th century. Rht‐B1b and Rht‐D1b increase plant productivity but also reduce single grain weight and protein content. Other alleles of Rht‐1 as well as other height‐affecting genes have been studied to provide breeders with alternative ways to modify plant height. To find Rht‐A1 alleles that could be used to fine tune plant height and other phenotypic traits that are affected by Rht‐1 , an ethyl methanesulfonate mutagenized Alpowa spring wheat population was screened for Rht‐A1 N‐terminal mutations. Nine mutations were identified and characterized through yeast two‐hybrid experiments to measure the impact each mutation had upon interaction with the gibberellin receptor GID1. Near isogenic lines were created by backcrossing the nine alleles into the cultivars Vida and Duclair, both with and without the semidwarfing allele Rht‐B1b , and tested in preliminary spaced‐plant trials. Five of these Rht‐A1 alleles (including a nonsense mutation allele, Rht‐A1 ‐Q6*) were selected for inclusion in full density yield trials. Only one mutant allele, Rht‐A1‐ E63K, consistently decreased height across tested backgrounds. This included a height decrease of 6 cm and a yield increase of 12% in a “tall” background when no other height reducing alleles were present. The Rht‐A1 ‐E63K mutation occurs within the LExLE motif where Rht ‐ B1b and Rht ‐ D1b mutations also occur, emphasizing the importance of this locus to the function of Rht‐1 .