Increasing wheat hardness locus functionality by increasing puroindoline copy number and introduction of novel alleles

Abstract

Wheat (Triticum aestivum L.) grain hardness affects many end product quality traits and is controlled primarily by the Hardness (Ha) locus that contains the Puroindoline a and b genes. All soft hexaploid wheats carry the same wild-type alleles Pina-D1a and Pinb-D1a and hard wheats carry a mutation in Pina or Pinb. In order to explore variation in the Puroindolines two approaches were pursued to increase Ha locus functionality. First Ha locus functionality was modified through a non-transgenic increase in Pin dosage. Here we tested the heritability and end product quality effects of increased Pin dosage in soft wheat. Previous experiments have suggested that grain softness can be enhanced by increasing Ha locus dosage via chromosome substitutions. Segregation data from a cross between a 'Chinese Spring' substitution lines with six doses of the Ha locus to the soft wheat variety 'Vanna' indicate that the substituted B genome Ha locus was not transmitted and that the A genome Ha locus was transmitted. Genotypes with the added Pins on the A genome produced seeds that were 7.4 hardness units softer.

These softer double Ha genotypes were lower in flour yields, but produced flour with lower ash content, reduced starch damage, and smaller mean particle size. The second route to increased Ha functionality was via novel Pin alleles present in synthetic hexaploid wheat (Triticum tauschii L.). Previous research has indicated that the seeds of synthetic hexaploid lines containing the PINAc or PINBh proteins are significantly softer than those carrying other alleles. Here we show lines containing the PINAc / PINBh or PINAa / PINBj Ha locus exhibited increases in flour ash and flour particle size as well as decreased kernel weight relative to lines carrying the PINAa / PINBa Ha locus. Further lines containing the PINAa / PINBj Ha locus exhibited increases in grain hardness and flour yield as well as decreased protein content relative to lines carrying the PINAa / PINBa Ha locus. The resultant phenotypes revealed a potentially useful intermediate hardness with improved product quality properties. Increasing the range of novel Ha loci may lead to increased soft wheat quality and marketability.