CYP76C2, an Arabidopsis thaliana cytochrome P450 gene expressed during hypersensitive and developmental cell death.

The characterisation of an Arabidopsis thaliana cytochrome P450-encoding cDNA clone, B72, preferentially expressed during the hypersensitive response (HR) provoked by the bacterial pathogen Pseudomonas syringae pathovar maculicola, is reported. The B72 cDNA clone corresponded to the CYP76C2 gene, which belongs to a small multigene family comprising four genes. HR-triggering bacteria harbouring different avirulence genes induced the accumulation of transcripts of this P450 gene. CYP76C2 gene expression was moreover associated with various processes leading to cell death such as leaf senescence, ageing of cell cultures, wounding as well as with treatment with the necrotising heavy metal salt, lead nitrate.

Structure of the Arabidopsis RPM1 gene enabling dual specificity disease resistance.

Plants can recognize pathogens through the action of disease resistance (R) genes, which confer resistance to pathogens expressing unique corresponding avirulence (avr) genes. The molecular basis of this gene-for-gene specificity is unknown. The Arabidopsis thaliana RPM1 gene enables dual specificity to pathogens expressing either of two unrelated Pseudomonas syringae avr genes. Despite this function, RPM1 encodes a protein sharing molecular features with recently described single-specificity R genes. Surprisingly, RPM1 is lacking from naturally occurring, disease-susceptible Arabidopsis accessions.

Perception and response in plant disease resistance.

Plants express sophisticated mechanisms for recognizing pathogens. The functionally defined repertoire of non-self perception is large; the number and nature of subsequent molecular events required for resistance is unknown. Recent cloning of disease resistance genes, and genetic identification of loci required for their function, allows dissection of the structure, evolution, and deployment within populations of pathogen-perception mechanisms. Roles for reactive oxygen species and programmed cell death in resistance have also been suggested recently. New results document a role for salicylic acid as a lynchpin in the establishment and maintenance of the 'effector functions' of disease resistance, and strategies for engineered plant protection are moving closer to reality.

hsr203J, a tobacco gene whose activation is rapid, highly localized and specific for incompatible plant/pathogen interactions.

A novel plant defense gene, hsr203J, whose corresponding mRNA accumulates preferentially during the incompatible interaction of tobacco (Nicotiana tabacum L.) with a pathogenic bacterium, Pseudomonas solanacearum, has been isolated and sequenced. No sequence homology of the putative product of this gene has been found in data bases. Evidence is presented here that the hsr203J gene promoter, when fused to the GUS reporter gene, is selectively expressed in response to the hypersensitive response (HR)-inducing bacteria in tobacco protoplasts and that the sequences responsible for this response are contained within 1.4 kb of the 5' noncoding region. The temporal and spatial patterns of hsr203J activation in leaves and roots inoculated with P. solanacearum indicate that the hsr203J promoter exhibits a rapid (3-6 h post-inoculation) and high level of induction only in plant cells inoculated with the HR-inducing bacterial isolate. In addition, this gene promoter which does not respond to various stress conditions and is only very weakly induced during compatible interactions, is strongly dependent on hrp (hypersensitive response and pathogenicity) genes of P. solanacearum. These data indicate that the hsr203J gene promoter exhibits new and original characteristics of activation with regard to the plant defense genes studied so far; its spatial and temporal program of activation together with its specific induction during the HR underline the importance of this gene as a molecular tool for studying the establishment and regulation of the HR.

Differential regulation in tobacco cell suspensions of genes involved in plant-bacteria interactions by pathogen-related signals.

Six cDNA clones whose corresponding mRNAs accumulate early during the hypersensitive reaction in tobacco leaves have been classified into 2 groups according to their maximum levels of accumulation in an incompatible versus a compatible interaction with Pseudomonas solanacearum. We present evidence that, at least in the first stages of the interaction, tobacco cell suspensions retain the ability to respond differentially to compatible and incompatible isolates of P. solanacearum. In addition, studies on the effect of a fungal elicitor on the accumulation of the mRNAs corresponding to the cDNA clones in cell suspensions indicate that only one group of genes responds to this treatment.

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).