Institute of Agrobiological Sciences, National Agriculture and Food Research Organization Owashi 1-2, Tsukuba, Ibaraki 305-8602, Japan; EditForce, Agri-Bio Research Laboratory, Ito Campus, Kyushu University 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
Institute of Agrobiological Sciences, National Agriculture and Food Research Organization Owashi 1-2, Tsukuba, Ibaraki 305-8602, Japan.
J Plant Physiol. 2020 Feb;245:153109. doi: 10.1016/j.jplph.2019.153109. Epub 2019 Dec 24.
OsERdj7 is one of six endoplasmic reticulum (ER)-resident J-domain-containing proteins (J-proteins) encoded by the rice genome that acts as a co-chaperone for Hsp70 and is characterized by the presence of two transmembrane domains. It is N-glycosylated and primarily exists in a dimeric form with a molecular mass of 64 kDa. When the microsomal fraction of maturing seeds was treated with alkaline, high salt or detergent compounds, OsERdj7 was solubilized, even in alkaline and high salt environments, indicating that it is not tightly integrated in the ER membrane. Next, to investigate its role during seed maturation, expression of OsERdj7 was specifically downregulated using RNA interference (RNAi) under the control of the endosperm-specific 16 kDa prolamin promoter in transgenic rice. As a result, the unfolded protein response (UPR) was induced in maturing seeds via activation of OsIRE1/OsbZIP50 and ATF6 orthologs, such as OsbZIP39 and OsbZIP60, leading to upregulation of several chaperones and folding enzymes. Furthermore, some prolamins (RM4 and RM9) were retained in the ER lumen in the form of a mesh-like structure without deposition to the inherent ER-derived protein bodies (PB-Is), although major storage protein glutelins were normally transported to protein storage vacuoles (PB-IIs). On the other hand, induction of ER associated degradation (ERAD) increased OsERdj7 expression in transgenic rice seeds in which ERAD related genes were highly expressed. Due to PDIL2-3 and OsHard3 co-immunoprecipitating with OsERdj7 in rice protoplasts, this result implicates OsERdj7 in the translocation of some seed proteins within the ER lumen and in the degradation of misfolded or unfolded proteins.
OsERdj7 是水稻基因组编码的六个内质网 (ER) 驻留 J 结构域蛋白 (J-proteins) 之一，作为 Hsp70 的共伴侣，其特征是存在两个跨膜结构域。它是 N-糖基化的，主要以二聚体形式存在，分子量为 64 kDa。当成熟种子的微粒体部分用碱性、高盐或去污剂化合物处理时，OsERdj7 可溶解，即使在碱性和高盐环境中也是如此，这表明它与内质网膜结合不紧密。接下来，为了研究其在种子成熟过程中的作用，使用 RNA 干扰 (RNAi) 在胚乳特异性 16 kDa 醇溶蛋白启动子的控制下，在转基因水稻中特异性下调 OsERdj7 的表达。结果，通过激活 OsIRE1/OsbZIP50 和 ATF6 同源物（如 OsbZIP39 和 OsbZIP60），在成熟种子中诱导未折叠蛋白反应 (UPR)，导致几种伴侣蛋白和折叠酶的上调。此外，一些醇溶蛋白（RM4 和 RM9）以网格状结构保留在内质网腔中，而没有沉积到固有 ER 衍生的蛋白体（PB-Is）中，尽管主要的贮藏蛋白谷蛋白正常运输到蛋白贮藏液泡（PB-IIs）中。另一方面，在高度表达 ER 相关降解 (ERAD) 相关基因的转基因水稻种子中，诱导 ERAD 增加了 OsERdj7 的表达。由于 PDIL2-3 和 OsHard3 在水稻原生质体中与 OsERdj7 共免疫沉淀，这一结果表明 OsERdj7 参与了一些种子蛋白在内质网腔中的易位和错误折叠或未折叠蛋白的降解。
