Mutational analysis of the Pseudomonas syringae pv. tomato hrpA gene encoding Hrp pilus subunit

Plant pathogenic Pseudomonas syringae strains harbour a type III secretion pathway suggested to be involved in the delivery of effector proteins from the bacteria into plant cells. During plant interaction, the bacteria appar ently produce surface appendages, termed Hrp pili, that are indispensable f or the secretion process. We have created an insertion mutation library, as well as deletion mutations to hrpA, the structural gene encoding Hrp pilin . Analysis of the mutants revealed gene regions important for hrpA expressi on, pilus assembly and pilus-dependent autoagglutination of the bacteria. T he majority of insertions in the amino-terminal half of the pilin were tole rated without bacterial interaction with plants being affected, while the c arboxy-terminus appeared to be needed for pilus assembly. Insertions in the 5' non-translated region and the first codons within the open reading fram e affected mRNA production or stability and abolished protein production.