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Title: Accumulation of leginsulin, a hormone-like bioactive peptide, is drastically higher in Asian than in North American soybean accessions

item Kim, Wonseok
item JANG, SUNGCHAN - University Of Missouri
item Krishnan, Hari

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2011
Publication Date: 11/17/2011
Citation: Kim, W., Jang, S., Krishnan, H.B. 2011. Accumulation of leginsulin, a hormone-like bioactive peptide, is drastically higher in Asian than in North American soybean accessions. Crop Science. 52:262-271.

Interpretive Summary: Soybean seeds accumulate several proteins including leginsulin, a cysteine-rich peptide. This peptide is lethal to certain insects. In addition to the insecticidal activities this bioactive peptide may also regulate blood glucose concentration in mammals. In spite of its potential role in signal transduction, defense response and glucose metabolism, very little is known about leginsulin expression, accumulation and distribution among soybean cultivars. In this study we demonstrate that the accumulation of leginsulin is prevalent among Asian cultivars and that the paucity of leginsulin accumulation in North American soybean cultivars is related to low level expression of leginsulin genes in the developing cotyledons. Our results provide new information on the distribution and accumulation of leginsulin. This information will be valuable for the soybean breeders and genetics to develop North American soybean cultivars with enhanced amounts of this bioactive peptide.

Technical Abstract: Leginsulin, a peptide made up of 37 amino acids, is homologous to pea albumin (PA1b) and belongs to the cysteine-knot family. Even though the physiological function and three-dimensional structure of leginsulin have been explored, little is known about their expression, accumulation and distribution among soybean cultivars. Antibody generated against leginsulin was used to screen a diverse array of soybean accessions from the USDA Soybean Germplasm Collection to identify soybean cultivars that are enriched in leginsulin. Analysis of 50% isopropanol-soluble proteins from 485 soybean lines by SDS-PAGE and Western blot analysis enabled the identification of 75 accessions that significantly accumulated leginsulin. Remarkably, all these accessions with the exception of two had their origin either from Japan, Korea or China. Leginsulin was barely detected in most of the commercial North American soybean cultivars used in this study. Western blot analysis revealed low accumulation of leginsulin in the embryonic axis but not in the cotyledons of soybean cultivar Williams 82 while in PI 458249 leginsulin was abundantly present in both types of tissue. Examination of the soybean cultivar Williams 82 genome sequence revealed the presence of two homologous leginsulin genes (Gm13g26330 [leginsulin 1] and Gm13g26340 [leginsulin 2]) on chromosome 13. We have cloned the two leginsulin genes from PI 458249 and found them to be highly similar to that of Williams 82. Northern blot analysis indicated that leginsulin mRNA was abundant in Williams 82 embryonic axis but not in the cotyledon. In contrast, leginsulin mRNA was abundantly present in PI 458249, both in the embryonic axis and the cotyledons.