ABSTRACT
ABSTRACT Tn5-induced mutations in Agrobacterium vitis F2/5 resulted in both altered grape necrosis and tobacco leaf panel collapse phenotypes, suggesting that the underlying mechanisms of the reactions are related. The reaction on tobacco resembles the classical hypersensitive response (HR) caused by several plant pathogenic bacteria in that it is observable within 14 h, is inhibited by treatment of plants with metabolic inhibitors, and results in the inability to recover the pathogen from the necrotic zone. Strains of A. vitis differ with regard to their efficiency of causing the reaction on tobacco. An EcoRI fragment from one mutant, M6, which is necrosis-altered and HR-minus, was cloned and sequenced. Sequence analysis revealed that the Tn5 insertion occurred in a region that shares significant homology with genes involved in long chain fatty acid production by the marine bacteria Shewanella spp. and Moritella marina. Complementation of M6 with a cosmid clone from an F2/5 DNA library restored the tobacco HR and grape necrosis phenotypes.
ABSTRACT
DNA sequencing of the Agrobacterium vitis pehA gene revealed a predicted protein with an M(r) of 58,000 and significant similarity to the polygalacturonases of two other plant pathogens, Erwinia carotovora and Ralstonia (= Pseudomonas or Burkholderia) solanacearum. Sequencing of the N terminus of the PehA protein demonstrated cleavage of a 34-amino-acid signal peptide from pre-PehA. Mature PehA accumulated primarily in the periplasm of A. vitis and pehA+ Escherichia coli cells during exponential growth. A. vitis PehA released dimers, trimers, and monomers from polygalacturonic acid and caused less electrolyte leakage from potato tuber tissue than did the E. carotovora and R. solanacearum polygalacturonases.
