Expression of unprocessed glutelin precursor alters polymerization without affecting trafficking and accumulation.
Rice glutelin is synthesized as a precursor in the endosperm endoplasmic reticulum and then deposited within the protein storage vacuole protein body-II (PB-II) as an aggregate, with a high degree of polymerized higher-order structure comprising mature acidic and basic subunits after post-translation processing cleavage. In order to investigate the functional role of this processing and its effect on folding assembly, wild-type GluA2 and its mutant cDNA (mGluA2), in which the conserved processing site (Asn-Gly) at the junction between the acidic and basic chains was replaced with Ala-Ala, were expressed under the control of the endosperm-specific GluB1 promoter in the mutant rice a123 line lacking glutelin GluA1, GluA2, and GluB4. The mGluA2 precursor was synthesized and stably targeted to PB-II without processing in the transgenic rice seeds like the wild-type GluA2. Notably, the saline-soluble mGluA2 precursor assembled with the other type of processed glutelin GluB as a trimer in PB-II, although such hetero-assembly with GluB was not detected in the transformant containing the processed GluA. Furthermore, the mGluA2 precursor in the glutelin fraction was deposited in PB-II by forming a quite different complex from the processed mature GluA2 products. These results indicate that post-translational processing of glutelin is not necessary for trafficking and stable accumulation in PB-II, but is required for the formation of the higher-order structure required for stacking in PB-II.
Wakasa
Yuhya
Y
Transgenic Crop Research and Development Center, National Institute of Agrobiological Sciences, Kannondai 3-1-3, Tsukuba, Ibaraki 305-8604, Japan.
Yang
Lijun
L
Hirose
Sakiko
S
Takaiwa
Fumio
F
D018506:Gene Expression Regulation, Plant; D005983:Glutens / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012275:Oryza / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011498:Protein Precursors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021381:Protein Transport
D011498:Protein Precursors; D005983:Glutens