A FERREDOXIN-LIKE GENE MAY BE INVOLVED IN RECOGNITION OF THE HARPINPSS DURING THE INDUCTION OF HYPERSENSITIVE RESPONSE
HAO-JAN LIN, BOR-HENG LEE and TENG-YUNG FENG
Institute of Botany, Academia Sinica, Nankang, Taipei 11529, Taiwan, ROC
The plant molecule that recognizes proteinaceous harpins, which elicits the hypersensitive response (HR) in non-host plants, is unknown. We found that the elicitor activity of harpinPss from Pseudomonas syringae pv. syringae can be delayed in the presence of an amphipathic protein, AP1 (22 kDa ), extracted from sweet pepper by an amphipathic extraction method. We initiated the cloning of the gene encoding the AP1 protein by using rapid amplification of cDNA ends (RACE) with degenerate primers designed from the N-terminal amino acids of AP1. One cDNA clone (pap1) was isolated from pepper containing a deduced N-terminal amino-acid sequence practically identical with the derived N-terminal amino-acid sequence of AP1. Comparison of the pap1 amino-acid sequence with the GeneBank database indicated that it has high homology with the ferredoxin I gene. The putative mature peptide region encoded an estimated 22-kDa protein in the Escherichia coli expression system, which is identical with the estimated molecular weight of the AP1 protein. Infiltration of the pap1 peptide and harpinPss mixture delayed the HR when compared to the infiltration of harpinPss alone. In a yeast two-hybrid system, co-transformation of pap1 and the hrpZ gene, which encodes harpinPss, showed an interaction. Based on these results, we hypothesize that the ferredoxin-like ap1 gene may play a role in the recognition of harpinPss during the induction of HR.