Plant amphipathic proteins delay the hypersensitive response caused by harpinPssandPseudomonas syringaepv.syringae

Harpin_Pssfrom the plant pathogenPseudomonas syringaepv.syringaeis a proteinaceous elicitor that induces a hypersensitive response (HR) in non-host plants. The plant products which recognize harpin_Pssin the triggering of the HR are not yet known. According to the elicitor-receptor model, we hypothesize that an exogenous cell membrane receptor infiltrated into the intercellular space will interfere with the interaction between harpin_Pssand the putative receptor. We demonstrate a plant amphipathic protein (AP1) which can postpone the HR induced by harpin_Pssas well asP. syringaepv.syringae.AP1 was extracted by solubilizing proteins from healthy leaves in the non-polar n-octanol buffer followed by a polar Tris buffer. The amphipathic extracts were then further separated by gel filtration and anion exchange chromatography to obtain highly purified AP1. Similar proteins can be extracted from cotton, tomato, and sweet pepper. The N-terminal amino acid sequence of AP1 is conserved among cotton, tomato, and sweet pepper. The postponement of the harpin_Pss-mediated HR was characterized as a competitive dosage-dependent pattern of AP1. An analysis of the bacterial population development indicates that the effect of AP1 on the postponement of bacteria-mediated HR was attributed to the suppression of bacterial growth during the early stages of the HR. The time course analysis of the infiltration indicates that the postponement of HR resulted from the co-interaction between AP1 and the bacteria. Based on these results, we suggest that the postponement of bacteria-mediated HR is due to the interference of the interaction between harpin_Pssand the putative receptor in the plant. Our research provides a new approach to elucidating the role that plants may play in the nonhost response caused by pathogens.