Poster: Protein targeting & vesicular trafficking

Abs # 648: mRNA targeting to endoplasmic reticulum subdomains regulates the protein localization in rice endosperm cells

Presenter:	Washida, Haruhiko , was@wsu.edu
Authors	Washida, Haruhiko  (A)   Sugino, Aya  (A)   Katsube-Tanaka, Tomoyuki  (A)   Sakulsingharoj, Chotipa  (A)   Kaneko, Sachiyo  (A)   Wang, Changlin  (A)   Okita, Thomas W. (A)
Affiliations:	(A): Institute of Biological Chemistry, Washington State University

The rice storage proteins are stored in different endomembrane compartments; prolamines assemble into intracisternal inclusion granules forming spherical ER-bounded protein bodies (PB-I) whereas glutelins are packaged via the Golgi into storage vacuoles (PB-II). The packaging of these proteins into different intracellular compartments may be due to their site of synthesis as their RNAs are segregated on different ER subdomains, PB-ER (PB-ER, prolamines) and cisternal ER (cis-ER, glutelins). To determine whether there is a relationship between RNA localization and protein targeting to distinct protein bodies, transgenic rice expressing sunflower 2S albumin (2SA), maize 10kD zein and hybrid storage protein genes were obtained, and used to study the localization of the RNAs and protein in developing endosperm cells. 10kD zein-3'nos RNAs were found to be distributed on the PB-ER and the proteins localized within PB-I. Replacement of 3'UTR with corresponding sequences from glutelin RNA, which contains a cis-ER targeting zip code, results in re-directing the localization of 10kD zein-3'glutelin RNA from PB-ER to cis-ER. Under these conditions, the 10kD zein protein was observed to be accumulated in PB-II. Similar to glutelins, 2SA RNA was targeted to cis-ER and the protein localized to PB-II. However, 2SA hybrid RNAs containing the 10kD zein signal peptide coding sequence, which contains a PB-ER targeting zip code, results in localization to both cis and PB-ER, and the 2SA protein is found in both PB-I and II. These results indicate that seed storage protein localization within the endomembrane compartments is correlated closely with RNA distribution to specific ER subdomains.