Leucine Zipper-Like Motifs of Hrpz(Pss) Are Not Essential to Induce Hypersensitive Response in Tobacco

Harpins are heat-stable, glycine-rich proteins secreted by several Gram-negative phytopathogenic bacteria, involved in the induction of hypersensitive response in non-host plants. HrpZ(Pss) is highly heat stable, exists as a poly-dispersed, multimeric protein in nature and the functional significance for its existence in many oligomeric forms, remains still unclear. It was suggested that the leucine zipper-like motifs (LZMs) may take part in the formation of oligomeric aggregates, which may be responsible for HR elicitation by harpins and for their high thermal stability. To test the involvement of LZMs in HR elicitation and induction of defense responses, we have generated deletion mutants with or without LZMs and analysed their ability to induce HR, and/or activate the defense responses. The deletion mutant HrpZMM1, with no LZM also elicited HR as well as defense responses in tobacco suggesting the LZMs are not essential for elicitor activity of HrpZ(Pss). However, the ability to elicit defense responses may be linked with the ability to induce HR.