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Plant Cell Rep (2013) 32:389399 DOI 10.1007/s00299-012-1372-3
ORIGINAL PAPER
Accumulation of rice prolaminGFP fusion proteins induces ER-derived protein bodies in transgenic rice calli
Takanari Shigemitsu Takehiro Masumura
Shigeto Morita Shigeru Satoh
Received: 9 September 2012 / Revised: 6 November 2012 / Accepted: 15 November 2012 / Published online: 29 November 2012 Springer-Verlag Berlin Heidelberg 2012
AbstractKey message We showed that rice prolamin polypep-tides formed ER-derived PBs in transgenic rice calli, and that this heterologous transgene expression system is suitable for studying the mechanism of rice PB-I formation.
Abstract Rice prolamins, alcohol-soluble seed storage proteins, accumulate directly within the rough endoplasmic reticulum (ER) lumen, leading to the formation of ER-derived type I protein bodies (PB-Is) in rice seed. Because rice prolamins do not possess a well-known ER retention signal such as K(H)DEL, or a unique sequence for retention in the ER such as a tandem repeat domain of maize and wheat prolamins, the mechanisms of prolamin accumulation in the ER and PB-I formation are poorly understood. In this study, we examined the formation mechanisms of PBs by expressing four types of rice prolamin species fused to green uorescent protein (GFP) in transgenic rice calli. Each prolaminGFP fusion protein was stably accumulated in rice calli and formed ER-derived PBs. In contrast, GFP fused with the signal peptide of prolamin was secreted into the intercellular
space in rice calli. In addition, each of the four types of prolaminGFP fusion proteins was co-localized with the ER chaperone binding protein. These results suggest that the mature polypeptide of prolamin is capable of being retained in the ER and induce the formation of PBs in non-seed tissue, and that the rice callus heterologous transgene expression system is useful for studying the mechanisms of rice PB-I formation.
Keywords Rice callus Prolamin Protein body GFP
Introduction
Plant seeds store storage proteins as a source of the nitrogen required for the germinating seedling. Almost all plant seed storage proteins are accumulated in special storage compartments called protein bodies (PBs). To date, various types of PBs have been identied in plant seeds. In maize endosperm, storage proteins are assembled into ER and then form ER-derived PBs (Lending and Larkins 1989). In wheat endosperm, storage proteins form PBs inside vacuoles (Rubin et al. 1992; Toshi et...