Interaction incompatible entre une bacterie phytopathogene Pseudomonas Solanacearum et le tabac (Nicotiana tabacum) : caracterisation de genes vegetaux

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Transcriptional activation of 2 classes of genes during the hypersensitive reaction of tobacco leaves infiltrated with an incompatible isolate of the phytopathogenic bacterium Pseudomonas solanacearum

Fourteen cDNA clones whose corresponding mRNAs accumulate during the hypersensitive reaction (HR) of tobacco leaves infiltrated with an incompatible strain of the bacterial pathogen Pseudomonas solanacearum have been subdivided by sequence homologies into 6 families. Studies on the accumulation of the mRNAs encoded by these genes in compatible and incompatible plant-bacterial interactions have been carried out and indicate that the 6 cDNA clones can be subdivided into 2 groups. In one group corresponding to 3 cDNA clones, the maximal level of mRNA accumulation is similar in both types of interaction, whereas in the other group, maximal mRNA accumulation in leaves undergoing an HR is 3- to 7-fold higher than in leaves infiltrated with the compatible strain. Within each group, the timing and kinetics of accumulation of the corresponding mRNAs differ for each individual cDNA clone. Run-on experiments indicate that transcriptional activation of these genes plays a major role in the control of their expression. Genomic hybridizations have been performed and indicate that the mRNAs corresponding to the cDNA clones are encoded by multigene families (6 to 20 genes)

Analysis of the synthesis of several pathogenesis-related proteins in tobacco leaves infiltrated with water and with compatible and incompatible isolates of Pseudomonas solanacearum

Pathogen attacks and treatment of many plant species by various chemicals induce the synthesis of pathogenesis-related (PR) proteins. These host-encoded, low molecular mass proteins have been well studied in tobacco reacting hypersensitively to infection by TMV. A partial cDNA clone encoding for β-1,3-glucanase was used as a probe to study the kinetics of accumulation of the corresponding mRNAs in tobacco leaves infiltrated with water or with compatible (K60), incompatible (GMI1000), and avirulent (GMI1178) isolates of a phytopathogenic bacterium, Pseudomonas solanacearum. A nonspecific accumulation of these transcripts, independent of the nature of the inoculum, was observed. Similar results were obtained with pCHN50, a chitinase-encoding cDNA clone. In addition, antibodies directed against several PR proteins were used to estimate the accumulation of these proteins in tobacco leaves infiltrated for 18 hr with the same P. solanacearum isolates or with water: no qualitative or quantitative difference could be detected. These data show that the stress provoked by our technique of infiltration of bacteria in leaves induces a nonspecific accumulation of these PR proteins. In addition, our results indicate that these polypeptides are not sufficient to provoke the appearance of necrotic lesions associated with the hypersensitive reaction