Expression and Localization of a 36-kDa Peptide Derived from a 24-kDa Vacuolar Protein (VP24) Precursor in Anthocyanin-Producing Sweet Potato Cells in Suspension Culture

Abstract

Expression and localization of a 36-kDa peptide (VP36) derived from a 24-kDa vacuolar protein (VP24) precursor were investigated in anthocyanin-producing sweet potato cells (Ipomoea batatas). VP24 is one of the major proteins in the anthocyanin-containing vacuoles, and synthesized as a large precursor protein that contains a C-terminal region in addition to the mature domain [Xu et al., Plant Physiol. (2001) 125: 447]. The accumulation patterns of both VP36 and VP24 were closely correlated with the accumulation of anthocyanin in the vacuoles. The immunocytochemical analysis using antibodies against the fusion protein containing a portion of the C-terminal peptide showed that VP36 was localized in intravacuolar pigmented globules (cyanoplasts) in a manner similar to VP24. These results further suggest that VP36 is a peptide derived from the VP24 protein precursor. Both VP36 and VP24 peptides are probably involved in formation of cyanoplasts in the anthocyanin-producing sweet potato cells.