The role of puroindoline A and B individually and in combination on grain hardness and starch association

Endosperm texture in wheat (Triticum aestivum L.) is an important criterion affecting end-product quality. Grain hardness is controlled by the Hardness (Ha) locus which contains the puroindoline a (Pina) and puroindoline b (Pinb) genes. Hard wheats possess mutations in Pina or Pinb while soft wheats possess the Pina-D1a and Pinb-D1a alleles. Here, we determined the role of PINA and PINB individually and in combination on grain hardness and association to starch. Pina-D1a or Pinb-D1a overexpressing transgenic lines were crossed to PINA or PINB null hard wheats. The crosses segregated for the transgene and the Ha locus. Random lines from each genotypic class were evaluated in replicated trials over 2 yr. Classes containing only native levels of PINA or PINB were hard textured. Homozygous classes with transgenic addition of PINA to the PINA(+)/PINB null Ha locus or addition of PINB to the PINA/PINB null Ha locus were intermediate in texture with grain hardness values of 43.5 and 45.5, respectively. Soft endosperm texture was only obtained when both PINA and PINB were present with the softest grain observed with addition of PINB to the PINA(+)/PINB null Ha locus. Association of high amounts of either puroindoline to starch required both PINA and PINB. The results indicate that PINA or PINB can act alone leading to intermediate-textured grain or can function together to give a soft grain texture.