28 Puroindolines: The molecular-genetic basis for wheat grain hardness.

C. F. MORRIS (1), M. J. Giroux (2), and M. Lillemo (3). (1) USDA, ARS, Western Wheat Quality Lab., Pullman, WA 99164; (2) Plant, Soil & Environ. Sci., Montana St. Univ., Bozeman, MT 59717; (3) Dept. Hort. & Crop Sci., Agric. Univ. Norway, N-1432 Aas, Norway.

A unique characteristic of wheat, as opposed to the other major cereal crops, is that it exists in 3 major hardness classes: soft and hard hexaploid and durum. The gene, Hardness, which controls the majority of variation among the three classes is the single most important quality gene in wheat. Grain hardness impacts nearly every aspect of milling, baking and utilization. With the report of friabilin in 1986, a new avenue opened to explore the molecular-genetic basis of grain hardness. After over a decade of research, puroindoline-the currently preferred name for friabilin-provides an evocative model for the expression of the Hardness gene. Our research has described two highly-conserved mutations, Pina-D1b and Pinb-D1b, that are associated with hard grain texture in hexaploid wheat. The first, Pina-D1b, involves a complete loss of puroindoline a mRNA and protein. The second, Pinb-D1b, results from a single nucleotide mutation and causes a change from Glycine to Serine at position 46. The apparent loss of function of either puroindoline a or b causes a change from soft endosperm to hard. The complete absence of both puroindolines is associated with the very hard texture of durum. Results of genotypic surveys indicate that 93% of 42 N. American hard winter wheats possess the Serine- type mutation (Pinb-D1b). Among 75 hard spring wheats, 84% possess this mutation. Among a set of 314 hard wheats of mostly Scandinavian origin, 93% posses the Serine mutation. In addition, the results of a comparison of grain hardness, milling and baking quality among a set of Pina-D1b X Pinb-D1b HRS recombinant inbred lines will be presented.