cDNA cloning and characterization of a plant protein that may be associated with the harpin(PSS)-mediated hypersensitive response

Hypersensitive response-assisting protein (HRAP) is a novel plant protein t hat can intensify the harpin(PSS)-mediated hypersensitive response (HR) in harpin(PSS)-insensitive plants, such as the vegetative stage of sweet peppe r. In this report, we identified a HRAP cDNA clone from sweet pepper (Capsi cum annuum cv. ECW). The sequence of this cDNA clone showed no appreciable similarity to any other known sequences. However, it contained three positi vely charged regions, a typical signal peptide and a cAMP-dependent phospho rylation site. The hrap mRNA accumulated preferentially during the incompat ible interaction of sweet pepper leaves with a pathogenic bacterium, Pseudo monas syringae pv. syringae. When the hrap gene transcription level was hig h, the sweet pepper leaves readily expressed the harpin(P)SS-mediated HR. T he hrap gene transcription level in sweet pepper was also higher during the reproductive stage than during the vegetative stage. The HRAP distribution in an individual plant and different plant species was investigated. We fo und that all the organs of sweet pepper, except fruit, could express two di fferent forms of HRAP. Moreover, the hrap gene was presented in many plant species including tobacco, Arabidopsis, and rice. In conclusion, our result s suggest that the hrap gene is widely distributed throughout the plant wor ld and its transcription level correlates with plant sensitivity to harpin( PSS). The interaction between HRAP and harpin(PSS) reveals a novel way to i nterpret the interaction mechanism between plants and bacterial pathogens.