Anderson Garrett H, Hanson Maureen R
Molecular Biology and Genetics, Cornell University, Ithaca, NY 14850, USA.
BMC Plant Biol. 2005 Feb 21;5:2. doi: 10.1186/1471-2229-5-2.
TOR, the target of the antibiotic rapamycin in both yeast and mammalian cells, is a potent cell growth regulator in all eukaryotes. It acts through the phosphorylation of downstream effectors that are recruited to it by the binding partner Raptor. In Arabidopsis, Raptor activity is essential for postembryonic growth. Though comparative studies suggest potential downstream effectors, no Raptor binding partners have been described in plants.
AtRaptor1B, a plant Raptor homologue, binds the AML1 (Arabidopsis Mei2-like 1) protein in a yeast two-hybrid assay. This interaction is mediated by the N-terminal 219 residues of AML1, and marks AML1 as a candidate AtTOR kinase substrate in plants. The AML1 N-terminus additionally carries transcriptional activation domain activity. Plants homozygous for insertion alleles at the AML1 locus, as well as plants homozygous for insertion alleles at all five loci in the AML gene family, bolt earlier than wild-type plants.
AML1 interacts with AtRaptor1B, homologue of a protein that recruits substrates for phosphorylation by the major cell-growth regulator TOR. Identification of AML1 as a putative downstream effector of TOR gives valuable insights into the plant-specific mode of action of this critical growth regulator.
TOR是抗生素雷帕霉素在酵母和哺乳动物细胞中的作用靶点，在所有真核生物中都是一种有效的细胞生长调节因子。它通过下游效应器的磷酸化发挥作用，这些效应器由结合伴侣Raptor招募到它那里。在拟南芥中，Raptor活性对于胚后生长至关重要。尽管比较研究表明了潜在的下游效应器，但尚未在植物中描述过Raptor结合伴侣。
AtRaptor1B是一种植物Raptor同源物，在酵母双杂交试验中与AML1（拟南芥Mei2样蛋白1）结合。这种相互作用由AML1的N端219个残基介导，并将AML1标记为植物中AtTOR激酶底物的候选物。AML1的N端还具有转录激活域活性。AML1基因座插入等位基因的纯合植物，以及AML基因家族所有五个基因座插入等位基因的纯合植物，比野生型植物更早抽薹。
AML1与AtRaptor1B相互作用，AtRaptor1B是一种蛋白质的同源物，该蛋白质为主要细胞生长调节因子TOR招募用于磷酸化的底物。将AML1鉴定为TOR的推定下游效应器，为这种关键生长调节因子的植物特异性作用模式提供了有价值的见解。
