The bacterial elicitor flagellin activates its receptor in tomato cells according to the address-message concept.
flg22, a peptide corresponding to the most conserved domain of bacterial flagellin, acts as a potent elicitor in plants. Here, we have used an iodinated derivative of flg22 ((125)I-labeled Tyr-flg22) as a molecular probe for the flagellin receptor in tomato cells. This radioligand showed rapid binding to a single class of specific, saturable, high-affinity receptor sites in intact cells and membrane preparations. Binding, although essentially nonreversible under physiological conditions, was not covalent, and chemical cross-linking was required to specifically label a single polypeptide of 115 kD. Intact flagellin and elicitor-active flagellin peptides but not biologically inactive analogs efficiently competed for binding of radioligand. Peptides lacking the C terminus of the conserved domain, previously found to act as competitive antagonists of elicitor action in tomato cells, also competed for binding of radioligand. Thus, this novel, high-affinity binding site exhibited all the characteristics expected of a functional receptor of bacterial flagellin. For a model of receptor activation, we propose a two-step mechanism according to the address-message concept, in which binding of the N terminus (address) is the first step and activation of responses with the C terminus (message) is the second step.
Meindl
T
T
Friedrich Miescher-Institute, P.O. Box 2543, CH-4002 Basel, Switzerland.
Boller
T
T
Felix
G
G
D000468:Alkalies; D000595:Amino Acid Sequence; D001667:Binding, Competitive / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005408:Flagellin / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007457:Iodine Radioisotopes; D018551:Solanum lycopersicum / Q000166:cytology / Q000378:metabolism*; D008566:Membranes / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D000468:Alkalies; D007457:Iodine Radioisotopes; D009842:Oligopeptides; D011956:Receptors, Cell Surface; D005408:Flagellin