Virulence-dependent induction of Hsp70/Hsc70 in tomato by Ralstonia solanacearum

The selective induction of heat shock protein(s) (HSP) in human cells during bacterial, parasitic or viral infection and the accompanying cytoprotection initiated an interest in this conserved group of proteins - either as markers of disease outcome and severity or in novel therapeutic approaches. Knowledge concerning the induction and role of HSP in plant-pathogen interactions is however limited. The objective of this study was to investigate the expression of constitutive and inducible members of the 70-kDa HSP family (Hsp70/Hsc70) during compatible and incompatible interactions in tomato Lycopersicon esculentum L. cv. UC82B. Cell suspensions were co-cultured with virulent (biovar III) or avirulent (biovar II) strains of Ralstonia solanacearum, the causative agent of bacterial wilt, and samples harvested at specific time points for the analysis of pathogenesis-related protein-1 (PR-1) accumulation, phenylalanine ammonia-lyase (EC 4.3.1.5, PAL) activity, Hsp70/Hsc70 accumulation and cell survival. Besides inducing PRA (6-18 h, P < 0.05), biovar II caused a virulence-dependent induction of Hsp70/Hsc70 (24-48 h, P < 0.05) coinciding with the induction of PAL activity (24-48 h, P < 0.05) and maintenance of cell viability (48 h). It is proposed that, at least in tomato, Hsp70/Hsc70 is induced by avirulent strains of R. solanacearum as part of the defence response to chaperone newly synthesized defence proteins and to maintain cellular homeostasis essential for the execution of a defence response. <(c)> 2001 Editions scientifiques et medicales Elsevier SAS.