CHARACTERIZATION OF A 34-KDA SOYBEAN BINDING-PROTEIN FOR THE SYRINGOLIDE ELICITORS

Syringolides are water-soluble, low-molecular-weight elicitors that tr igger defense responses in soybean cultivars carrying the Rpg4 disease -resistance gene but not in rpg4 cultivars, I-125-syringolide 1 previo usly was shown to bind to a soluble protein(s) in extracts from soybea n leaves, A 34-kDa protein that accounted for I-125-syringolide 1 bind ing activity was isolated with a syringolide affinity-gel column, Part ial sequences of internal peptides of the 34-kDa protein were identica l to P34, a previously described soybean seed allergen, In soybean see ds, P34 is processed from a 46-kDa precursor protein and was shown to have homology with thiol proteases, P34 is a moderately abundant prote in in soybean seeds and cotyledons but its level in leaves is low, cDN As encoding 46-, 34-, and 32-kDa forms of the soybean protein were clo ned into the baculovirus vector, pVL1392, and expressed in insect cell s, The resulting 32- and 34-kDa proteins, but not the 46-kDa protein, exhibited ligand-specific I-125-syringolide binding activity, These re sults suggest that P34 may be the receptor that mediates syringolide s ignaling.