Title : Identification of kunitz-free soybean lines by the application of different marker types
Abstract:
The primary protease inhibitors in soybean, Kunitz trypsin inhibitor (KTI) and Bowman-Birk inhibitor (BBI), account for at least 6% of the protein in soybean seeds. Trypsin inhibitors (TI) are responsible for the reduced digestibility of seed proteins, making them the major anti-nutritional components in soybeans. Conventional soybean varieties require heat processing to deactivate the activity of trypsin inhibitors before being used as animal feed. The breeding program at the Maize Research Institute Zemun Polje has made significant progress in lowering the TI activity in soybean grain by developing a promising breeding lines from the crosses of standard high-yielding varieties with a donor parent lacking KTI. Marker-assisted selection (MAS) appeared to be an efficient tool for speeding up the selection for KTI-free lines, allowing for identification of desirable plants in early generations with a minimum quantity of plant tissue and without losing valuable seed samples. Identification of KTI-free lines in segregating generations is performed by the application of two molecular markers proposed to be tightly linked to KTI locus – Satt228 and Satt409. The segregation ratio for the presence or absence of KTI among breeding lines was 3:1, as it was expected for the monogenic trait controlled by a single locus. Both markers yielded the identical results regarding the DNA profiles of the examined soybean lines, indicating their reliability for the early-generation selection of KTI-free lines. Results generated from SSR analysis were validated by the acrylamide sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). There was a strong correlation between the protein band for Kunitz trypsin inhibitor protein at the position of 21,5 kDa and the Satt228 and Satt409 marker's banding pattern. Therefore, those two markers can be strongly proposed for the application in MAS for low KTI in soybean grain. Soybean varieties with reduced protease inhibitor content could reduce or eliminate the need for expensive and time-consuming heat treatments and minimise the possibility of a decrease in soybean seed protein solubility and essential amino acid availability.
