Marker‐assisted backcrossing of a null allele of the α‐subunit of <scp>S</scp>oybean (<i><scp>G</scp>lycine max</i>) β‐conglycinin with a <scp>C</scp>hinese soybean cultivar (a). The development of improved lines

Abstract

Abstract The development of soybean varieties that lack the β‐conglycinin α‐subunit is an attractive goal because the β‐conglycinin α‐subunit negatively influences the nutrition and gelation of tofu and is a major allergen. To remove this undesirable allergen and simultaneously improve the seed nutritional value and food‐processing quality, marker‐assisted background selection ( MABS ) was used in backcross breeding to incorporate cgy‐2 , a null phenotype version of the gene encoding the β‐conglycinin α‐subunit, from the donor line ‘ R i B ’ into the genetic background of the C hinese cultivar ‘ D ongnong47’ ( DN 47), a popular high‐oil superfine seed soybean cultivar from H eilongjiang P rovince, C hina. In each F 2 ( F 2 , BC n F 2 ) generation of the breeding programme, the offspring that carried the introgressed cgy‐2 were identified by sodium dodecyl sulphate–polyacrylamide gel electrophoresis and rescreened by MABS using simple sequence repeat markers to accelerate recurrent parent genome recovery. Of the 49 advanced backcrossing breeding lines ( ABL s), the three best lines, ABL 1, ABL 2 and ABL 3, were selected from the BC 1 , BC 2 and BC 3 populations, respectively. The ABL s were evaluated for desirable agronomic characteristics, yield‐related traits, amino acid composition, free amino acid composition and tofu‐processing quality in the mature seeds. All of the ABL s lacked the α‐subunit but grew and reproduced normally without deleterious effects on physiological processes such as seed development and germination. The free amino acid content of ABL 1 was significantly higher than that of ‘ DN 47’, with arginine ( A rg) being particularly enriched. Compared to the recurrent parent ‘ DN 47’, the total protein content of the three ABL s was higher, the amino acid composition of the seed proteins was markedly modified and the yield and hardness of the tofu that was made from the ABL s were significantly increased. MABS combined with stringent phenotypic selection in a backcross breeding programme is a feasible strategy for the genetic engineering of seed protein components to produce allergenic subunit‐deficient variant alleles.