title: Expression of ER quality control-related genes in response to changes in BiP1 levels in developing rice endosperm.
abstract: Binding protein (BiP) is the key chaperone involved in folding of secretory proteins such as seed storage proteins in the ER lumen. To obtain functional information about BiP1, a gene that is predominantly expressed during rice seed maturation, we generated several transgenic rice plants in which various levels of BiP1 protein accumulated in an endosperm-specific manner. Severe suppression (BiP1 KD) or significant over-expression (BiP1 OEmax) of BiP1 not only altered seed phenotype and the intracellular structure of endosperm cells, but also reduced seed storage protein content, starch accumulation and grain weight. Microarray and RT-PCR analyses indicated that expression of many chaperone and co-chaperone genes was induced in transgenic plants, with more prominent expression in the BiP1 KD line than in the BiP1 OEmax line. Transcriptional induction of most chaperones was observed in calli treated with dithiothreitol or tunicamycin, treatments that trigger ER stress, indicating that induction of the chaperone genes in transgenic rice was caused by an ER stress response. In transient assays using rice protoplasts, the ortholog (Os06g0622700) of the AtbZIP60 transcription factor was shown to be involved in activation of some chaperone genes. Slight increases in the BiP1 level compared with wild-type, accompanied by increased levels of calnexin and protein disulfide isomerase-like proteins, resulted in significant enhancement of seed storage protein content, without any change in intracellular structure or seed phenotype. Judicious modification of BiP1 levels in transgenic rice can provide suitable conditions for the production of secretory proteins by alleviating ER stress.
authors.affiliation: Transgenic Crop Research and Development Center, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki 305-8602, Japan.
authors.forename: Yuhya
authors.initials: Y
authors.lastname: Wakasa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yasuda
authors.forename: Youko
authors.initials: Y
authors.lastname: Oono
authors.forename: Taiji
authors.initials: T
authors.lastname: Kawakatsu
authors.forename: Sakiko
authors.initials: S
authors.lastname: Hirose
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Shimpei
authors.initials: S
authors.lastname: Hayashi
authors.forename: Lijun
authors.initials: L
authors.lastname: Yang
authors.forename: Fumio
authors.initials: F
authors.lastname: Takaiwa
mesh_terms: D050976:Basic-Leucine Zipper Transcription Factors / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D056625:Endosperm / Q000166:cytology*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D018832:Molecular Chaperones / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D012275:Oryza / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D012639:Seeds / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D018832:Molecular Chaperones; D010940:Plant Proteins; D018749:RNA, Plant