HRP PILUS - AN HRP-DEPENDENT BACTERIAL SURFACE APPENDAGE PRODUCED BY PSEUDOMONAS-SYRINGAE PV TOMATO DC3000

Hypersensitive response and pathogenicity (hip) genes control the abil ity of major groups of plant pathogenic bacteria to elicit the hyperse nsitive response (HR) In resistant plants and to cause disease in susc eptible plants. A number of Hrp proteins share significant similaritie s with components of the type III secretion apparatus and flagellar as sembly apparatus In animal pathogenic bacteria, Here we report that Ps eudomonas syringae pv., tomato strain DC3000 (race 0) produces a filam entous surface appendage (Hrp pilus) of 6-8 nm in diameter in a solid minimal medium that Induces hip genes, Formation of the Hrp pilus is d ependent on at least two hip genes, hrpS and hrpH (recently renamed hr cC), which are involved in gene regulation and protein secretion, resp ectively, Our finding of the Hrp pilus, together with recent reports o f Salmonella typhimurium surface appendages that are involved in bacte rial invasion into the animal cell and of the Agrobacterium tumefacien s virB-dependent pilus that is involved in the transfer of T-DNA into plant cells, suggests that surface appendage formation is a common fea ture of animal and plant pathogenic bacteria in the infection of eukar yotic cells, Furthermore, we have identified HrpA as a major structura l protein of the Hrp pilus, Finally, we show that a nonpolar hrpA muta nt of P. syringae pv, tomato DC3000 is unable to form the Hrp pilus or to cause either an HR or disease in plants.