Mutagenesis of the Wild Type Puroindoline b in a Pina Null Hard Wheat Variety Increases Grain Hardness and Flour Particle Size

Wheat (Triticum aestivum L.) grain hardness is controlled by the tightly linked genes Puroindoline a (Pina) and b (Pinb), resident at the Hardness (Ha) locus. Wheats with a functional Pina and Pinb are soft textured while those with mutations in either gene are hard textured. A single mutation in either Pina or Pinb increases grain hardness by ~30 hardness units and the majority of U.S. hard wheat varieties contain one of just two common Pina or Pinb mutations. However, no wheats have been reported to have nonsense mutations in both Pina and Pinb. Prior studies have identified wheat varieties containing Ha locus deletions but no studies have tested the impact of mutations in the remaining wild type Pin in hard wheats without a Ha deletion. We created and tested two independent stop codon mutations in Pinb using the hard wheat variety Fortuna. Fortuna carries the Pina-D1c allele, a nonsense allele. The two Pinb stop codon genotypes were crossed back to Fortuna and F₂ lines were selected that were either PINA null or PINA/B null. Seed from PINA/B null F₂ genotypes derived from both independent stop codon alleles were 6-8 units harder than those having only the PINA nonsense allele. Flour from PINA/B nulls was higher in average particle size and in starch damage as well. The PINA/B null genotype demonstrates that the loss of both PINs leads to grain hardness increases that may be useful to breeding programs to modify wheat end product quality.