The genetic improvement of protein quality in common bean (Phaseolus vulgaris L.)

Abstract The common bean (Phaseolus vulgaris L.) has a high seed protein content, between 20 and 30%. The protein quality in common is considered low because of the suboptimal levels of methionine and cysteine in the seed. Phaseolin, the main seed storage protein, accounts for 30-50% of the total seed protein content. Phaseolin only contains about 0.5 to 0.80% methionine. The suggested nutritional requirements for methionine-cysteine in the human diet are between 2.5 and 2.6 %. Previous studies on the germplasm SMARC1N-PN1 showed that deficiency in phaseolin and lectins leads to increased methionine-cysteine up to 2.6% in the bean seed. Dr. Hou, the bean breeder in Manitoba, made a cross between SMARC1N-PN1 and Morden-003. One Hundred and eighty-five recombinant inbred lines (RILs) F2:8 were obtained of this cross through eight generations of inbreeding. In this study I used SDS-PAGE to assess the protein profiles of the RILs according to the phenotypic expression for phaseolin and lectins. The RILs deficient in phaseolin and lectins increased their total methionine-cysteine seed content up to 3.4%. Field trials were conducted to assess the impact of the protein deficiency on the RILs’ agronomic traits. The RILs deficient in phaseolin and lectins had a similar agronomic performance as Morden-003 thus can be considered Canadian elite germplasm to develop common bean cultivars with improved protein. Key-words: Phaseolus vulgaris, SDS-PAGE, phaseolin, methionine, cysteine, recombinant inbreed line