Cloning of soybean genes induced during hypersensitive cell death caused by syringolide elicitor

Syringolide elicitors produced by bacteria expressing Pseudomonas syringae pv. glycinea avirulence gene D (avrD) induce hypersensitive cell death (HCD) only in soybean (Glycine max [L.] Merr.) plants carrying the Rpg4 disease resistance gene. Employing a differential display method, we isolated 13 gene fragments induced in cultured cells of a soybean cultivar Harosoy (Rpg4) treated with syringolides. Several genes for isolated fragments were induced by syringolides in an rpg4 cultivar Acme as well as in Harosoy; however, the genes for seven fragments designated as SIH (for syringolide-induced/ HCD associated) were induced exclusively or strongly in Harosoy. cDNA clones for SIH genes were obtained from a cDNA library of Harosoy treated with syringolide. Several sequences are homologous to proteins associated with plant defense responses. The SIH genes did not respond to a non-specific beta-glucan elicitor, which induces phytoalexin accumulation but not HCD, suggesting that the induction of the SIH genes is specific for the syringolide-Harosoy interaction. HCD and the induction of SIH genes by syringolides were independent of H(2)O(2). On the other hand, Ca(2+) was required for HCD and the induction of some SIH genes. These results suggest that the induction of SIH genes by syringolides could be activated through the syringolide-specific signaling pathway and the SIH gene products may play an important role(s) in the processes of HCD induced by syringolides.