Marker-assisted stacking of null Kunitz trypsin inhibitor and off-flavour generating lipoxygenase-2 in soybean

Soybean varieties genetically free from Kunitz trypsin inhibitor (KTI) and lipoxygenase-2 (Lox2) are desirable to increase human consumption, as the former is an antinutritional factor that affects protein digestibility while the latter is a principal contributor to off-flavour. In the present investigation, soybean genotypes free from both these undesirable components were developed by introgression of null allele of Lox2 from NRC109 (lox2lox2) into two KTI-free soybean genotypes derived from genotypes JS97-52 and NRC7. Foreground selection of plants in F1, F2, BC1F1, BC1F2, BC2F1 and BC2F2 generations developed from two cross combinations i.e. NRC7-derived KTI-free genotype (N7KTIF)×NRC109 (parental combination 1) and JS97-52 derived KTI free genotype (JKTIF)×NRC109 (parental combination 2) was performed using null allele specific markers and tightly linked simple sequence repeat (SSR) markers for both KTI and Lox2 genes for the identification of homozygous recessive (titilox2lox2) plants. Background selection was performed using 239 and 241 polymorphic SSR markers across the genome. This resulted in the development of 9 and 13 soybean lines stacked for null alleles of both KTI and Lox2 (titilox2lox2) exhibiting recurrent parent genome content more than 97 and 96%, respectively. Days-to-flowering, days-to-maturity, 100-seed weight and yield per plant of the stacked lines developed from both the parental combinations were at par with the respective recurrent parents.

Development of Breeder-Friendly KASP Markers for Low Concentration of Kunitz Trypsin Inhibitor in Soybean Seeds

Trypsin inhibitors (TI), a common anti-nutritional factor in soybean, prevent animals’ protein digestibility reducing animal growth performance. No commercial soybean cultivars with low or null concentration of TI are available. The availability of a high throughput genotyping assay will be beneficial to incorporate the low TI trait into elite breeding lines. The aim of this study is to develop and validate a breeder friendly Kompetitive Allele Specific PCR (KASP) assay linked to low Kunitz trypsin inhibitor (KTI) in soybean seeds. A total of 200 F3:5 lines derived from PI 547656 (low KTI) X Glenn (normal KTI) were genotyped using the BARCSoySNP6K_v2 Beadchip. F3:4 and F3:5 lines were grown in Blacksburg and Orange, Virginia in three years, respectively, and were measured for KTI content using a quantitative HPLC method. We identified three SNP markers tightly linked to the major QTL associated to low KTI in the mapping population. Based on these SNPs, we developed and validated the KASP assays in a set of 93 diverse germplasm accessions. The marker Gm08_44814503 has 86% selection efficiency for the accessions with low KTI and could be used in marker assisted breeding to facilitate the incorporation of low KTI content in soybean seeds.

Bowman-Birk inhibitor in soybean: Genetic variability in relation to total trypsin inhibitor activity and elimination of Kunitz trypsin inhibitor

Bowman-Birk inhibitor (BBI) is a soybean seed serine protease inhibitor whose nutraceutical properties far exceed its anti-nutritional property arising from its trypsin and chymotrypsin inhibitor activity. High BBI soybean genotypes are sought for the commercial preparation of this nutraceutical biomolecule while low BBI content in Kunitz trypsin inhibitor (KTI)-free genetic background is desirable in soymeal manufacturing. In the present investigation, monoclonal antibody assay of 95 soybean genotypes revealed 11-fold genetic variation for BBI concentration. The study led to the identification of 3 very high (>20 mg/g defatted soy flour) and 5 very low BBI (< 4 mg/g defatted soy flour) soybean genotypes. Contribution of BBI to total trypsin inhibition activity ranged from 2.2 to 53.5% with average value of 11.6%. Genotypes with varying level of BBI raised consecutively for two years exhibited non-significant (p>0.05) effect of growing year on the trait. BBI content in BC3F2 derived KTI-free lines was at par with the recurrent parent. Low and high BBI content genotypes with diverse genetic background identified in the study may be exploited to develop mapping population to identify genomic regions underlying BBI in soybean.

Breeding of Black Soybean with Green Cotyledon and Four Recessive Alleles for Lipoxygenase, Kunitz Trypsin Inhibitor, Lectin, and Stachyose

Anthocyanins from the black soybean seed coat are known to have many pharmaceutical effects. However, black soybean seed contains antinutritional factors such as lipoxygenase, Kunitz trypsin inhibitor (KTI), lectin, and stachyose. The genetic removal of these components will improve the nutritional value of black soybean seed. The objective of this research was to breed a soybean strain with the black seed coat color, green cotyledon color, and tetra recessive allele (lox1lox2lox3/lox1lox2lox3-ti/ti-le/le-rs2/rs2) for lipoxygenase, KTI, lectin, and stachyose components. Eight parents were used to breed the tetra null strain. Analysis of lipoxygenase, KTI, lectin, and stachyose components in mature seeds was conducted by SDS-PAGE, Western blot, and HPLC. The soybean line with the black seed coat color, the green cotyledon color, a large seed size, and tetra recessive alleles has purple flowers, a determinate growth habit, and brown pods at maturity. The stem height of the breeding line was 52.3 cm. The 100-seed weight of the breeding line was 35.2 g and the yield (Ton/ha) was 2.50. The stachyose content of the breeding line was 3.30 g/kg. This is the first soybean strain with the black seed coat color, the green cotyledon color, a large seed size, and tetra null alleles (lox1lox2lox3/lox1lox2lox3-ti/ti-le/le-rs2/rs2, low content of stachyose, free of lipoxygenase, KTI, and lectin proteins).

Identification of a filamentous form of kunitz protease inhibitor in Asteraceae

Filamentous structures were observed in purified extracts from chrysanthemum, gerbera, sunflower and zinnia. When purified filament proteins were subjected to SDS-PAGE, the major protein associated with filaments from all three species has an apparent molecular mass of ≈25 kDa. Protein bands from chrysanthemum, gerbera, and zinnia were subjected to N-terminal protein sequencing while proteins from sunflower were sequenced by CID MS/MS. All of the sequences shared highest similarity to the kunitz trypsin inhibitor family. The sequencing results indicated that the proteins lacked the signal sequences. We tested the gerbera filament protein for glycosylation and found that it was a glycoprotein. Together these results indicate that the filaments are composed of mature KTI protein. This is the first report of a KTI assembling into filaments and the first report of a filament forming Asteraceae enzyme.

Combining the null Kunitz trypsin inhibitor and yellow mosaic disease resistance in soybean (Glycine max (L.) Merrill)

For the wide adoption of soybean varieties, it is desirable, that they are Kunitz trypsin inhibitor (Kti) free and resistant to yellow mosaic disease (YMD). The soybean variety SL525 with YMD resistance was crossed with the YMD susceptible variety NRC101 with a null kti allele. The F₅progeny derived from the cross was screened with two simple sequence repeat (SSR) markers (satt409 and satt322) linked with the null kti allele and the YMD resistance, respectively, and one null kti allele-specific marker. The presence of both desirable traits was further confirmed with the phenotypic data which showed good correlation with the genotypic data. The yield potential of fourteen such identified genotypes having both desirable traits was either at par or superior to SL525, hence, represent improved versions of SL 525.

Correlations of grain yields and yield components among mother's and full-sib progenies of soybean

The F2 population was developed by crossing the adaptive yield variety of soybean with a variety without the Kunitz trypsin inhibitor in the mature grain. From the segregating F2 population 48 plants were taken. Their seeds were used to set up field experiment; part of the seed was saved for full-sib (FS) crosses. After yield testing, three lines marked as L6, L30 and L38 were chosen. Two FS cross combination, using saved seeds, were made (L30 x L38 and L6 x L30). Progenies of soybean full-sibs (FSF1:2) and each mother plant (F3:4) were grown, to make enough seed for testing in the field experiment. Data obtained in this experiment were processed to determine correlations of grain yield and other studied traits between mother's and proper full-sib progenies, using simple correlations and Spearman's rank correlations. A significant correlation into examinated traits between two types of progenies does not found, except for stem height and 1000 grain weight in the FS combination L30 x L38. The lack of correlation of plant characteristics between progenies of full-sibs and their mothers indicated the influence of lines used as fathers component. In both combinations of FS crosses, FSF1:2 progenies with better yield than the adapted parent (one without Kunitz trypsin inhibitor) were identified, which are considered promising for the further process of creating new varieties.