Expression of pathogenicity and virulence related genes in Pseudomonas syringae pv. syringae under copper stress

Stone fruit bacterial canker is one of the most destructive diseases of apricot in Iran. Copper-based compounds are widely used to protect plants against bacterial diseases, but pathogens frequently evolve resistance against copper (Cu). This study was conducted to investigate the genetic diversity of the Cu resistance gene copA among strains of the causal agent of canker disease of stone fruits Pseudomonas syringae pv. syringae (Pss), isolated from apricot trees in East Azarbaijan province of Iran. The phylogenic trees based on copA and rpoD are very similar to each other revealing no evidence of recombination. To test the hypothesis that pathogenicity- and virulence-related genes may be induced by Cu in Pss strains, quantitative real-time polymerase chain reaction (qRT-PCR) was used to evaluate the expression of genes algD, copA, fliC, hrpA, syrB and tatC, in the Cu sensitive Pss 170 strain upon exposure to Cu. Among the tested genes, the algD and copA involved in alginate synthesis and Cu resistance, respectively, showed the highest increase in expression compared to a non-copper (control): 4.75-fold and 2.68-fold, respectively. Based on these results and on the conservation of genes algD and copA in Pseudomonas pathovars, antimicrobials that target AlgD and CopA proteins should be developed to use in combination with Cu to increase control efficiency.