The hrp genes of Pseudomonas cichorii are essential for pathogenicity on eggplant but not on lettuce

1 Laboratory of Plant Pathology and Biotechnology, Kochi University, 200 Monobe, Nankoku, Kochi 783-8502, Japan 2 Institute of Molecular Genetics, Kochi University, 200 Monobe, Nankoku, Kochi 783-8502, Japan Correspondence Yasufumi Hikichi yhikichi{at}cc.kochi-u.ac.jp Pseudomonas cichorii causes necrotic lesions in eggplant and rot in lettuce. Through transposon insertion into P. cichorii strain SPC9018 we produced two mutants, 4-57 and 2-99, that lost virulence on eggplant but not lettuce. Analyses showed that a transposon was inserted into the hrpG gene in 4-57 and the hrcT gene in 2-99. Nucleotide sequences of the hrp genes of SPC9018 are homologous to those of Pseudomonas viridiflava BS group strains. The pathogenicity of 4-57 on eggplant was restored by transformation with an hrpF operon, originating from either SPC9018 or the BS group member P. viridiflava strain 9504 (Pv9504). These data suggested the involvement of hrp genes in the pathogenicity of SPC9018 on eggplant, and functional conservation of hrpF operons between SPC9018 and Pv9504. Both the hrpS mutant and the hrpL mutant were unable to cause necrotic lesions on eggplant leaves but retained their pathogenicity against lettuce. These results suggest that the pathogenicity of P. cichorii is hrp -dependent in eggplant, but not in lettuce. Abbreviations: PCD, programmed cell death; TTSS, type III secretion system The GenBank/EMBL/DDBJ accession numbers for the hrp genes of SPC9018 and the hrpF operon of Pv9504 are AB433910 and AB434833, respectively.