Molecular Plant Pathology – Pathogen Profiles

From host recognition to T-DNA integration: the function of bacterial and plant genes in the Agrobacterium–plant cell interaction]

Tzvi Tzfira and Vitaly Citovsky
Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, NY 11794-5215, USA

Summary: Agrobacterium tumefaciens and its related species, A. rhizogenes and A. vitis, are the only known bacterial pathogens which ‘genetically invade’ host plants and stably integrate part of their genetic material into the host cell genome. Thus, A. tumefaciens has evolved as a major tool for plant genetic engineering. Further-more, this unique process of interkingdom DNA transfer has been utilized as a model system for studies of its underlying biological events, such as intercellular signalling, cell-to-cell DNA transport, protein and DNA nuclear import and integration. To date, numerous bacterial proteins and several plant proteins have been implicated in the A. tumefaciens–plant cell interaction. Here, we discuss the molecular interactions among these bacterial and plant factors and their role in the A. tumefaciens–plant cell DNA transfer. 
Taxonomic relationship:Bacteria; Proteobacteria; alpha subdivision; Rhizobiaceae group; Rhizobiaceaefamily; Agrobacterium genus. 
Microbiological properties: Gram-negative, nonsporing, motile, rod-shaped, soil-borne. 
Related species: A. rhizogenes (causes root formation in infected plants), A. vitis (causes gall formation on grapevines). 
Disease symptoms: Formation of neoplastic swellings (galls) on plant roots, crowns, trunks and canes. Galls interfere with water and nutrient flow in the plants, and seriously infected plants suffer from weak, stunted growth and low productivity. 
Host range: One of the widest host ranges known among plant pathogens; can potentially attack all dicotyledonous plant species. Also, under controlled conditions (usually in tissue culture), can infect, albeit with lower efficiency, several monocotyledonous species. 
Agronomic importance: The disease currently affects plants belonging to the rose family, e.g. apple, pear, peach, cherry, almond, roses, as well as poplar trees (aspen).