Abstract
Rice α-amylase I-1 (AmyI-1) is a secretory glycoprotein bearing a typical N-linked oligosaccharide chain. However, it was found that α-amylase is involved in degradation of plastidial starch in living cells. Furthermore, the traffic of ER-to-Golgi was shown to be necessary for targeting AmyI-1-GFP into plastid in onion epidermal cell system, indicating that possible existence of a traffic route of AmyI-1 from the endomembrane system to plastids.
To clarify the plastidial targeting route of AmyI-1, simultaneous expression of trans-Golgi and plastid markers, ST-mRFP and WxTP-GFP, in onion cells was performed. In the cells expressing fluorescent trans-Golgi and plastid markers, they frequently co-localized when co-expressed with AmyI-1. Three-dimensional time-lapse imaging in onion cells and electron microscopy of high-pressure frozen/freeze-substituted rice cells demonstrated that contact and subsequent absorption of the Golgi-derived membrane vesicles with cargo into plastids occur in the cells.
