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Flour Protein Composition and Functional Properties of Transgenic Rye Lines Expressing HMW Subunit Genes of Wheat

¹Deutsche Forschungsanstalt für Lebensmittelchemie, Lichtenbergstr. 4, D-85748 Garching, Germany. ²Corresponding author. E-mail: h.wieser@lrz.tum.de ³University of Florida - IFAS, Agronomy Department, PMCB, Genetics Institute, 2191 Mc Carty Hall, Laboratory of Molecular Plant Physiology, Gainesville FL 326611-0300.

Flours from nonsprouted (ns) kernels and dried sprouted (s) kernels of transgenic rye expressing HMW glutenin subunits (HMW-GS) 1Dy10 (L10) or 1Dx5+1Dy10 (L5+10) from wheat were compared with flours from the corresponding wildtype rye (Lwt). The crude protein content of nonsprouted flours ranged from 9.2% (Lwt) to 10.4% (L5+10) and was lowered by ≈1% due to sprouting. Flour proteins were separated into albumins/globulins, prolamins, and glutelin subunits by a modified Osborne fractionation and into SDS-soluble and insoluble fractions. Portions of the prolamin fractions were reduced in the same manner as glutelins. The different fractions were then characterized and quantified by RP-HPLC on C₈ silica gel. The proportion of albumins/globulins did not significantly differ between transgenic lines and wildtype. The proportions of alcohol-insoluble glutelins and SDS-insoluble proteins drastically increased in transgenic rye due to a shift of HMW and γ-75k secalins into the polymeric fractions. Significant differences in the proportion of highly polymeric proteins between nonsprouted and sprouted flours could not be detected. The quantitative data demonstrated that the expression of HMW-GS led to a higher degree of polymerization of storage proteins in rye flour. The HMW-GS combination 1Dx5+1Dy10 showed stronger effects than 1Dy10 alone. The analyzed flours contained two HMW secalins (R1, R2), whose amino acid compositions were closely related to those of 1Dy10 and 1Dx5, respectively. The amounts of R1 in Lwt flours determined by RP-HPLC were 221 mg (ns) and 186 mg (s) per 100 g and those of R2 were 344 mg (ns) and 298 mg (s), respectively. These amounts increased to 240 mg (ns)/201 mg (s) (R1) and 479 mg (ns)/432 mg (s) (R2) in L10 flours. In L5+10 flours, the amount of R1 decreased to 150 mg (ns)/132 mg (s) while R2 increased to 432 mg (ns)/338 mg (s). The amount of HMW-GS 1Dy10 was almost the same as that of R2 in L10 flours but was strongly increased in L5+10 flour (633 mg [ns]/538 mg [s]). HMW-GS 1Dx5 was, by far, the major subunit in L5+10 flours (987 mg 7[ns]/896 mg [s]). The summarized amounts of all HMW subunits increased from ≈0.5 g (Lwt) to ≈1.1 g (L10) and ≈2.0 g (L5+10). Thus only L10 flours were similar to wheat flours in HMW subunit content. The baking performance of L10 flour determined by a microbaking test was improved compared with Lwt flour, whereas L5x10 flour showed very poor properties obviously due to the strongly increased proportion of highly cross-linked glutelins. The breadmaking quality of flours from 1Dy10 seeds and wildtype seeds was reduced by the same degree when flours from sprouted seeds were analyzed.