A vacuolar sorting determinant of soybean β-conglycinin β subunit resides in a C-terminal sequence

Abstract

β-Conglycinin (7S globulin), one of the major storage proteins of soybean, is a trimeric protein composed of α (67 kDa), α′ (71 kDa) and β (50 kDa) subunits and exhibits molecular heterogeneity. It is synthesized on the endoplasmic reticulum and transported to the protein storage vacuole (PSV). In this study, we examined a vacuolar sorting determinant (VSD) of the β subunit using seeds of transgenic Arabidopsis accumulating deletion derivatives of β subunit. We found that the β subunit was transported to the matrix and the globoid compartment of the PSV through distinct pathways, and that a VSD to the matrix resides in the C-terminal 10 amino acids. We further verified that the C-terminal 10 amino acids of β subunit are sufficient to transport green fluorescent protein to the PSV matrix in soybean seed cells by using transient expression system. The results of this study show a transport mechanism for the β subunit similar to that of the α′ subunit [Plant J., 34 (2003) 647].