HOPA1’ A NEW PUTATIVE T3SS EFFECTOR OF PSEUDOMONAS SAVASTANOI PV. SAVASTANOI STRAIN DAPP-PG722, THE CASUAL AGENT OF OLIVE KNOT DISEASE

Recently, we reported the draft genome sequence of the Italian DAPP-PG722 strain of Pseudomonas savastanoi pv. savastanoi (Psv), which shows about 85% identity with the Psv genome of the French strain NCPPB3335. Since the Italian strain is less virulent than the French strain in both lignified and young micropropagated olive plants, bioinformatic analysis was performed to verify whether the difference in virulence is dependent on the effector repertoire of the two strains. Results showed that the two strains shared an identical T3SS repertoire, except for a new putative effector, named hopA1’, which is absent in the NCPPB3335 strain. In the DAPP-PG722 Psv genome, the hopA1’ gene is present in an incomplete hrc/hrp gene cluster. Phylogenetic analysis between the amino acid sequence of HopA1’ and those of the HopA1 and HopA2 present in several strains of the P. syringae complex, revealed a high identity of HopA1’ with HopA2 of P. syringae pv. aesculi strain 2250. Dot blot analysis and southern hybridization were carried out to verify the presence of hopA1’ among 35 Psv strains and 26 strains of the P. syringae complex isolated from herbaceous and woody plants. HopA1’ is present in a single copy in the chromosomal DNA of the DAPP-PG722 strain as well as in others 12 Psv strains and 5 strains of the P. syringae complex attacking woody plants. To investigate the role of hopA1’ in Psv virulence the mutant of this gene in the strain DAPP-PG722 and its ectopic expression in NCPPB3335 strain are in progress