title: Insights into the TOR-S6K signaling pathway in maize (Zea mays L.). pathway activation by effector-receptor interaction.
abstract: The primordial TOR pathway, known to control growth and cell proliferation, has still not been fully described for plants. Nevertheless, in maize, an insulin-like growth factor (ZmIGF) peptide has been reported to stimulate this pathway. This research provides further insight into the TOR pathway in maize, using a biochemical approach in cultures of fast-growing (FG) and slow-growing (SG) calli, as a model system. Our results revealed that addition of either ZmIGF or insulin to SG calli stimulated DNA synthesis and increased the growth rate through cell proliferation and increased the rate of ribosomal protein (RP) synthesis by the selective mobilization of RP mRNAs into polysomes. Furthermore, analysis of the phosphorylation status of the main TOR and S6K kinases from the TOR pathway revealed stimulation by ZmIGF or insulin, whereas rapamycin inhibited its activation. Remarkably, a putative maize insulin-like receptor was recognized by a human insulin receptor antibody, as demonstrated by immunoprecipitation from membrane protein extracts of maize callus. Furthermore, competition experiments between ZmIGF and insulin for the receptor site on maize protoplasts suggested structural recognition of the putative receptor by either effector. These data were confirmed by confocal immunolocalization within the cell membrane of callus cells. Taken together, these data indicate that cell growth and cell proliferation in maize depend on the activation of the TOR-S6K pathway through the interaction of an insulin-like growth factor and its receptor. This evidence suggests that higher plants as well as metazoans have conserved this biochemical pathway to regulate their growth, supporting the conclusion that it is a highly evolved conserved pathway.
authors.affiliation: Biochemistry Department, Chemistry Faculty, UNAM , Mexico City 04510, Mexico.
authors.forename: Verónica
authors.initials: V
authors.lastname: Garrocho-Villegas
authors.forename: Raúl
authors.initials: R
authors.lastname: Aguilar C
authors.forename: Estela
authors.initials: E
authors.lastname: Sánchez de Jiménez
mesh_terms: D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D059828:Plant Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D010940:Plant Proteins / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D011132:Polyribosomes / Q000187:drug effects / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D011972:Receptor, Insulin / Q000819:agonists / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013002:Somatomedins / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects; D003313:Zea mays / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*
chemical_list: D007328:Insulin; D010940:Plant Proteins; D013002:Somatomedins; C434664:zea-mays insulin-like growth factor; D011972:Receptor, Insulin; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases