Abstract
Rice α-globulin is a 2S albumin-type seed storage protein that accumulates in the protein storage vacuole (PB-II) in starchy endosperm. We constructed GFP fusions with different regions of α-globulin to identify the vacuolar-targeting signal. The localizations of the fusion proteins and prolamin protein bodies (PB-I) stained with Rhodamine in developing endosperm were simultaneously analyzed by confocal microscopy. GFP fused with the N-terminal region (M1-S43) was mostly present in dilated ER till 12 DPA, in which single or multiple PB-I were frequently visualized. Subsequently, the GFP fusion protein was efficiently transported from the dilated ER to PB-II by 18 DPA. GFP in protein bodies was sequestered to the periphery and matrix that surrounds crystalloids containing glutelins. Since the signal peptide (M1-A22) is cotranslationaly cleaved, we conclude that an efficient vacuolar-targeting signal for α-globulin exists in the N-terminal region from Q23 to S43.
