Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2011
Publication Date: June 1, 2011
Citation: Thomashow, L.S., Mavrodi, D.V., Hassan, K.A., Paulsen, I.T., Loper, J.E., Alfano, J.R., Weller, D.M. 2011. Novel pathways revealed in P. fluorescens Q2-87 and Q8r1-96. Phytopathology. 101:S231. Technical Abstract: Pseudomonas fluorescens Q2-87 and Q8r1-96, both from a take-all decline field in Quincy, Washington, U.S.A., are almost indistinguishable in vitro, but only strain Q8r1-96 exhibits the “premier” phenotype distinguished by highly aggressive wheat root colonizing ability essential for the natural disease suppressiveness known as take-all decline (TAD). Despite their phenotypic similarity, comparison of the complete genomic sequences of Q2-87 and Q8r1-96 revealed that Q8r1-96 has 1,373 genes (22.8% of its genome) not present in Q2-87. These include 658 hypothetical and conserved hypothetical ORFs, 88 regulators, 70 transport and membrane proteins, and various enzymes, toxins, transposases, phages, etc. The two strains probably belong to different serovars; a large O-antigen biosynthesis cluster present in Q8r1-96 is very similar to that from serovar O-5 of P. aeruginosa and likely was acquired by horizontal gene transfer. Both Q2-87 and Q8r1-96 harbor type III secretion systems. The Q8r1-96 genome encodes three effectors, one of which has no known homologues. Q8r1-96 effectors are secreted in culture, injected into plant cells, and can suppress effector- and PAMP-triggered immune responses in tobacco. However, expression of the Q8r1-96 T3SS in the rhizosphere of wheat or pea had only a minor effect on colonization.