Essential cell growth regulator that controls development from early embryo to seed production. Controls plant growth in environmental stress conditions. Acts through the phosphorylation of downstream effectors that are recruited by the binding partner RAPTOR. Acts by activating transcription, protein synthesis and ribosome biogenesis, and inhibiting mRNA degradation and autophagy. Can phosphorylate TAP46, a regulatory subunit of protein phosphatase 2A that modulates cell growth and survival (PubMed:21216945). Involved in modulating the transition from heterotrophic to photoautotrophic growth by regulating the expression of chloroplast- and photosynthesis-associated genes (PubMed:27479935). Essential for auxin signaling transduction, probably acting in polysomes to maintain the active ATPK1/S6K1 (and thus TIF3H1/eIF3h) phosphorylation status that is critical for translation reinitiation (e.g. uORF-mRNAs loading) (PubMed:23524850, PubMed:27014314). Promotes abscisic acid (ABA) biosynthesis (PubMed:26459592). Involved in the regulation of sugar-mediated (e.g. glucose and sucrose) glycolysis- and mitochondrial bioenergetics-dependent root growth promotion (PubMed:23542588). Required for sugar (e.g. glucose) promotion of hypocotyl elongation in the dark, by activating the brassinosteroid pathway and stabilizing BZR1. The regulation of BZR1 degradation is dependent on autophagy (PubMed:27345161). Regulates the expression, phosphorylation and ribosome association of MRFs (e.g. MRF1, MRF3 and MRF4), especially under energy-deficient conditions (PubMed:29084871). (Microbial infection) Binding to cauliflower mosaic virus (CaMV) Tav protein is critical for both translation reinitiation and viral fitness (PubMed:21343906). When activated by CaMV P6, promotes CaMV translation by inhibiting cellular autophagy and suppressing both silencing and innate immunity, thus confering sensitivity to P.syringae (PubMed:27120694). (Microbial infection) Required during infection by some potyvirus such as Watermelon mosaic virus (WMV) but not for turnip mosaic virus (TuMV). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Almost insensitive to rapamycin (PubMed:23963679). Strongly repressed by specific active site inhibitors (asTORis) such as AZD-8055, TORIN2 and WYE-132, and, to a lesser extent, by KU63794, WYE-354 and TORIN1, leading to impaired photoautotrophic growth and abnormally early meristematic cells differentiation (PubMed:23963679, PubMed:23524850). Repression by TORIN1 leads to impaired responses to auxin, including gravitropism (PubMed:23524850). Combined treatment with rapamycin and active-site inhibitors (e.g. Torin1 and AZD-8055) results in synergistic inhibition of activity and plant growth (PubMed:27479935). Inhibition by KU63794 leads to reduced auxin content in root tips (PubMed:27014314). AZD-8055 treatment reduces abscisic acid (ABA) levels (PubMed:26459592). In addition, inhibition by AZD-8055 leads to a strong reduction of watermelon mosaic virus (WMV) infection (PubMed:25979731). Interacts with RAPTOR1 and itself. Interacts with FKBP12 in a rapamycin-dependent manner. Binds to LST8-1 (PubMed:22307851). Hyperactivated upon interaction with cauliflower mosaic virus (CaMV) Tav protein (PubMed:21343906). Associates to polysomes when activated by auxin or cauliflower mosaic virus (CaMV) Tav protein. A number of isoforms are produced. According to EST sequences. Highly expressed in root meristems, shoot apical meristem (SAM) and floral buds. One day after fertilization, expressed in endosperm, embryo, and the chalazal proliferating tissue. At globular stage, no longer expressed in endosperm, but still in embryo up to the heart and torpedo stages. In mature embryo, expressed in the apical and primary root meristems and dividing vascular tissues. During lateral root formation, expressed in the lateral root primordia and remains during the formation of the emerging secondary root meristem. Activation by auxin triggers recruitment to polysomes which release inactive ATPK1/S6K1. The kinase domain is required for its function. Activated by phosphorylation on Ser-2424 triggered by cauliflower mosaic virus P6 and auxin. Embryo lethality when homozygous. Premature arrest of endosperm and embryo development. RNAi mutant exhibits plant growth arrest and reduced expression of brassinosteroid (BR)-responsive genes, as well as abolished exogenous sugar-mediated promotion of BZR1 accumulation (PubMed:27345161). RNAi plants are impaired in sugar-mediated (e.g. glucose and sucrose) root growth promotion and associated genes expression (PubMed:23542588). In response to auxin, deficient plants have polysomes prebound by inactive ATPK1/S6K1, and loading of uORF-mRNAs and activation TIF3H1/eIF3h are impaired (PubMed:23524850). In RNAi plants, severe alteration of watermelon mosaic virus (WMV) infection, but only slight delay of turnip mosaic virus (TuMV) infection (PubMed:25979731). Deficient plants are resistant to viral infection by cauliflower mosaic virus (CaMV), by failing to support CaMV Tav protein-mediated transactivation of reinitiation (PubMed:21343906). Inducible silencing in seedlings or adult plants leads to plant growth arrest. Plants slightly silencing TOR show constitutive autophagy and reduced shoot and root growth, leaf size, seed production and resistance to osmotic stress. Plants overexpressing TOR show increased shoot and root growth, leaf size, seed production and resistance to osmotic stress. Plants expressing FKBP12 (BP12) are sensitive to rapamycin. BP12 plants repressed by rapamycin exhibit slower growth and development leading to poor nutrient uptake and light energy utilization. Belongs to the PI3/PI4-kinase family.