Site-specific Accumulation Mechanism of Rice Prolamin within Type I Protein Body

Abstract

Prolamins, one of major rice seed storage proteins, accumulate within the endoplasmic reticulum (ER) and form the type I protein body (PB-I). Our previous study demonstrated that the 10 kDa, 13 kDa (13a, 13b), and 16 kDa prolamins are regularly stacked in layers within the PB-I. However, the site-specific accumulation mechanism of rice prolamin within the PB-I remains unclear. In this study, the influence of promoter and mature polypeptide for the accumulation site within the PB-I was investigated by using green fluorescence protein (GFP) as reporter protein.
The transgenic rice plants expressing the GFP or 13a prolamin-GFP fusions under the CaMV35S promoter or own promoter were produced (35S_pro:GFP, 35S_pro:13a-GFP, 13a_pro:13a-GFP). The GFP proteins localized in the cytosol of the 35S_pro:GFP seed, whereas the 13a-GFP localized in the core within PB-I of 35S_pro:13a-GFP. However, 13a-GFP localized the peripheral region of PB-I in the 13a_pro:13a-GFP seed. These findings show the importance of the prolamin molecules and the gene expression regulation controlled by the promoter in the site-specific accumulation of prolamins within PB-I.