MOTIVATION: The hypersensitive response (HR) is a process activated by plants after microbial infection. Its main phenotypic effects are both a programmed death of the plant cells near the infection site and a reduction of the microbial proliferation. Although many resistance genes (R genes) associated to HR have been identified, very little is known about the molecular mechanisms activated after their expression. RESULTS: The analysis of the product of one of the R genes, the Hin1 protein, led to the identification of a novel domain, which we named WHy because it is detectable in proteins involved in Water stress and Hypersensitive response. The expression of this domain during both biotic infection and response to desiccation points to a molecular machinery common to these two stress conditions. Moreover, its presence in a restricted number of bacteria suggests a possible use for marking plant pathogenicity. CONTACT: francesca.ciccarelli@embl.de SUPPLEMENTARY INFORMATION: Supplementary data (Figures S1 and S2 and Table S1) and the alignment in clustal format are available at http://www.bork.embl.de/~ciccarel/WHy_add_data.html.