Increased Wheat Grain Hardness Conferred by Novel Puroindoline Haplotypes from Aegilops tauschii

The Puroindoline genes (Pine and Pinb) together comprise the wheat (Triticum aestivum L.) Hardness locus (Ha) located on chromosome 5D and control grain texture. While hard wheats contain a mutation in either Pina or Pinb, there is no puroindoline allelic diversity among soft hexaploid wheats as all carry the Pina-D1a/Pinb-D1a alleles. However, Pina and Pinb allelic variation exists within synthetic hexaploid wheats created using novel D genome donors. Here we tested the effects of four Aegilops tauschii-derived Ha locus haplotypes (Pina-D1c/Pinb-D1h, Pina-D1e/Pinb-D1i, Pina-D1a/Pinb-D1i, and Pina-D1j/Pinb-D1i) found in synthetic wheats by crossing them into the soft white spring wheats 'Alpowa' and 'Vanna'. The effect of each Ha haplotype on grain hardness was measured by analyzing backcross or F-2-derived lines. All novel Ha loci increased grain hardness while still conditioning soft wheat texture independent of durum or Ae. tauschii synthetic wheat parent line. The Pina-D1c/Pinb-D1h haplotype was found to increase grain hardness relative to the wild-type Ha locus by an average of 6.5 units, Pina-D1e/Pinb-D1i by 5.6 units, Pina-D1a/Pinb-D1i by 12.6 units, and Pina-D1j/Pinb-D1i by 3.8 units. None of the novel Ha locus haplotypes significantly affected Pina or Pinb transcript or protein expression levels. The results indicate that Ae. tauschii derived novel Ha loci could be useful in modifying soft wheat grain texture and end product quality.