Accumulation of Leginsulin, a Hormone‐Like Bioactive Peptide, is Drastically Higher in Asian than in North American Soybean Accessions

Abstract

ABSTRACTLeginsulin, a peptide made up of 37 amino acids, is homologous to pea (Pisum sativum L.) 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 its expression, accumulation, and distribution among soybean [Glycine max (L.) Merr.] accessions. An antibody generated against leginsulin was used to screen a diverse array of soybean accessions from the USDA Soybean Germplasm Collection to identify soybean accessions that are enriched in leginsulin. Analysis of 50% isopropanol‐soluble proteins from 485 soybean lines by sodium dodecyl sulfate polyacrylamide gel electrophoresis (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 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 North American soybean cultivar Williams 82 while in the Chinese 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 (Gm13 g26330 [leginsulin 1] and Gm13 g26340 [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 messenger RNA (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.