Maegawa Kentaro, Takii Rumi, Ushimaru Takashi, Kozaki Akiko
Department of Biology, Shizuoka University, 836 Ohya Suruga-ku, Shizuoka, 422-8529, Japan.
Mol Genet Genomics. 2015 Oct;290(5):2019-30. doi: 10.1007/s00438-015-1056-0. Epub 2015 May 9.
Target of rapamycin (TOR) is a conserved eukaryotic serine/threonine kinase that functions as a central controller of cell growth. TOR protein is structurally defined by the presence several conserved domains such as the HEAT repeat, focal adhesion target (FAT), FKBP12/rapamycin binding (FRB), kinase, and FATC domains starting from the N-terminus. In most eukaryotes, TOR forms two distinct physical and functional complexes, which are termed as TOR complex 1 (TORC1) and TORC2. However, plants contain only TORC1 components, i.e., TOR, Raptor, and LST8. In this study, we analyzed the gene structure and functions of TORC components in rice to understand the properties of the TOR complex in plants. Comparison of the locations of introns in these genes among rice and other eukaryotes showed that they were well conserved among plants except for Chlamydomonas. Moreover, the intron positions in the coding sequence of human Raptor and LST8 were closer to those of plants than of fly or nematode. Complementation tests of rice TOR (OsTOR) components in yeast showed that although OsTOR did not complement yeast tor mutants, chimeric TOR, which consisted of the HEAT repeat and FAT domain from yeast and other regions from rice, rescued the tor mutants, indicating that the HEAT repeat and FAT domains are important for species-specific signaling. OsRaptor perfectly complemented a kog1 (yeast Raptor homolog) mutant, and OsLST8 partially complemented an lst8 mutant. Together, these data suggest the importance of the N-terminal region of the TOR, HEAT, and FAT domains for functional diversification of the TOR complex.
雷帕霉素靶蛋白（TOR）是一种保守的真核丝氨酸/苏氨酸激酶，作为细胞生长的中央控制器发挥作用。TOR蛋白在结构上由几个保守结构域定义，例如从N端开始的HEAT重复序列、粘着斑靶点（FAT）、FKBP12/雷帕霉素结合（FRB）、激酶和FATC结构域。在大多数真核生物中，TOR形成两种不同的物理和功能复合物，分别称为TOR复合物1（TORC1）和TORC2。然而，植物仅含有TORC1的组分，即TOR、Raptor和LST8。在本研究中，我们分析了水稻中TORC组分的基因结构和功能，以了解植物中TOR复合物的特性。比较水稻和其他真核生物中这些基因内含子的位置，结果表明，除衣藻外，它们在植物中保守性良好。此外，人类Raptor和LST8编码序列中的内含子位置与植物的比与果蝇或线虫的更接近。酵母中水稻TOR（OsTOR）组分的互补试验表明，虽然OsTOR不能互补酵母tor突变体，但由酵母的HEAT重复序列和FAT结构域以及水稻的其他区域组成的嵌合TOR拯救了tor突变体，这表明HEAT重复序列和FAT结构域对于物种特异性信号传导很重要。OsRaptor完全互补了kog1（酵母Raptor同源物）突变体，OsLST8部分互补了lst8突变体。总之，这些数据表明TOR的N端区域、HEAT和FAT结构域对于TOR复合物功能多样化的重要性。
