ACTIVATION OF HSR203, A PLANT GENE EXPRESSED DURING INCOMPATIBLE PLANT-PATHOGEN INTERACTIONS, IS CORRELATED WITH PROGRAMMED CELL-DEATH

hsr203J is a tobacco gene whose activation is rapid, highly localized, and specific for incompatible interactions between tobacco and the ba cterial pathogen Ralstonia solanacearum, The effect of other hypersens itive response (HR)-inducing pathogens and elicitors has been tested w ith transgenic plants containing the hsr203J promoter-GUS reporter gen e fusion, and confirms the generality of the preferential inducibility of the hsr203J gene promoter during incompatible interactions: bacter ial and viral pathogens inducing an HR in tobacco were able to induce the promoter fusion, as were inducers of KR-like responses such as har pin, elicitins, and PopA1 proteins. A tomato hsr203 homologous cDNA wa s isolated (Lehsr203) and used to examine the effect of avr gene produ cts on the expression of such genes. Lehsr203 was shown to be rapidly and transiently induced in leaves of the tomato Cf-9 line, following A vr9 product infiltration, but not in those of the Cf-0 line. Among pot ential effecters of HR or resistance such as H2O2, salicylic acid, met hyl jasmonate, and 2,6-dichloro-isonicotinic acid (INA), none is able to induce a significant increase in promoter activation. In contrast, heavy metals that cause leaf necrosis can trigger such an activation. In addition, hsr203-GUS fusion expression is detected in transgenic to bacco lines expressing the bO gene and exhibiting spontaneous HR-like lesions. Taken together, these results demonstrate a strong correlatio n between hsr203 and genetically controlled cell death in tobacco and tomato. The expression of this gene should be a useful marker for prog rammed cell death occurring in response not only to diverse pathogens, but also to diverse death-triggering extracellular agents.