Identification of novel virulence genes and metabolic pathways required for full fitness of Pseudomonas savastanoi pv. savastanoi in olive (Olea europaea) knots

Comparative genomics and functional analysis of Pseudomonas syringae and related pathogens have mainly focused on diseases of herbaceous plants; however, there is a general lack of knowledge about the virulence and pathogenicity determinants required for infection of woody plants. Here, we applied signature-tagged mutagenesis (STM) to Pseudomonas savastanoi pv. savastanoi during colonization of olive (Olea europaea) knots, with the goal of identifying the range of genes linked to growth and symptom production in its plant host. A total of 58 different genes were identified, and most mutations resulted in hypovirulence in woody olive plants. Sequence analysis of STM mutations allowed us to identify metabolic pathways required for full fitness of P. savastanoi in olive and revealed novel mechanisms involved in the virulence of this pathogen, some of which are essential for full colonization of olive knots by the pathogen and for the lysis of host cells. This first application of STM to a P. syringae-like pathogen provides confirmation of functional capabilities long believed to play a role in the survival and virulence of this group of pathogens but not adequately tested before, and unravels novel factors not correlated previously with the virulence of other plant or animal bacterial pathogens. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.This work was supported by the Spanish MINECO grants AGL08-05311 and AGL11-30343-C02-01, co-financed by FEDER. IMM was supported by the Ramón Areces Foundation (Spain). We thank D. Holden (Imperial College, London, UK) for kindly providing the collection of tagged miniTn5Km2 transposons. A. de Vicente and A.J. Jimenez are thanked for help with the analysis of virulence inolive plants and for the preparation and microscopic visualization of olive knot sections, respectively. C. Beuzon and J.Ruiz-Albertare thanked for valuable advice regarding STM screening. We thank M. Duarte for excellent technical assistance. We are grateful to A. Barcelo and I. Imbroda for the micropropagation of olive plants.Peer Reviewe