Characterization of an axis-specific protein from mungbean expressed late during seed maturation

A low molecular weight (LMW) protein found in abundance in the dry axis of mungbean (Vigna radiata L. Wilczek) was purified to homogeneity. Its pI was found to be 7.9. Antibody raised against the protein was used to screen a cDNA library made from maturing mungbean embryo (18–19 d after flowering) in an expression vector system, λ-gt11. A full-length cDNA clone (VRLEA12.1) encoding the polypeptide was isolated by immunoscreening. The cDNA sequence showed a single major open reading frame for a highly hydrophilic, 112 amino acid polypeptide of relative molecular mass 14 192 Da. Messenger RNA and protein accumulate specifically in the embryonic axis and not in any other part of the plant under normal conditions. The protein is synthesized starting 9 d after flowering and accumulates until seed desiccation with the greatest amount found in the dry seed; northern analysis also confirmed this. Sequence homology and differential expression reveals that this is an abscisic acid-responsive protein encoded by a multigene family.