A novel cucumber gene associated with systemic acquired resistance

Several genes were isolated by differential display of mRNAs from cucumber leaves inoculated with the bacterium, Pseudomonas syringae pv. lachrymans. A full-length cDNA encoding a novel pathogen-induced gene, Cupi4, was cloned and characterized in detail. While Cupi4 did not share evident homology with known sequences in the database at the nucleotide level, the predicted amino acid sequence of Cupi4 shared homology with the pathogen-inducible proteins, pMB57-10G 5′ of Brassica napus (21%) and CXc750/ESC1 of Arabidopsis thaliana (16%). Cupi4 transcripts accumulated after 12 h in leaves inoculated with P. s. lachrymans and after 48 h in the systemic upper leaves of the inoculated plants. Treatment with the chemical inducers of systemic acquired resistance (SAR), salicylic acid, 2,6-dichloroisonicotinic acid and benzothiadiazole as well as inoculation with different pathogens, P. s. syringae, Colletotrichum lagenarium and tobacco necrosis virus also led to the accumulation of Cupi4 transcripts. The increase of Cupi4 transcripts in both the inoculated first leaf and in systemic upper leaves suggested that the Cupi4 gene product is associated with systemic acquired resistance in cucumber. Induced expression of CUPI4 in different host strains of a bacterium, Escherichia coli, led to death of bacterial host cells, suggesting that CUPI4 might have antibacterial properties.