Puroindolines : their control over wheat grain hardness and influence on milling and bread baking traits

Abstract

Wheat grain is sold based upon several physiochemical characteristics, one of the most important being grain texture. Grain texture in wheat directly affects many end use qualities such as milling yield, break flour yield, and starch damage. The Hardness (Ha) locus located on the short arm of chromosome 5D is known to control grain hardness in wheat. This locus contains the puroindoline a (pina) and puroindoline b (pinb) genes. All wheats to date that have mutations in pina or pinb are hard textured, while wheats possessing both the 'soft type' pina-D1a and pinb-D1a sequences are soft. Furthermore, it has been shown that complementation of the pinb-D1b mutation in hard spring wheat can restore a soft phenotype. Here, the first objective was to identify and characterize the effect the puroindolines have on grain texture independently and together. The second objective was to determine which milling bread baking characteristics are affected by the seed specific over-expression of puroindolines. To accomplish both of these objectives a hard red spring wheat, possessing the pinb-D1b mutation, was transformed with 'soft type' pina and pinb, creating transgenic isolines that have added pina, pinb, or pina and pinb.

Northern blot analysis of developing control and transgenic lines indicated that grain hardness differences were correlated with the timing of the expression of the native and transgenically added puroindolines. The addition of PINA decreased grain hardness less than the reduction seen with added PINB. Friabilin abundance was correlated with the presence of both 'soft type' PINA and PINB and did not correlate well with total puroindoline abundance. Selected T3 lines were grown in a field trial with two replications under dry and irrigated field conditions. Harvested grain was then milled and baked. Lines transformed with the puroindolines exhibited decreased total flour yields and increased break flour yields, yielding flour with lower protein and ash content. Decreases in loaf volume, mixograph absorption, and crumb grain scores were also observed in transgenic lines. These results demonstrate that the puroindolines can be used to profoundly influence grain hardness and a variety of milling and bread baking traits in wheat.