Why is Ralstonia solanacearum Race 3 cold tolerant? Using post-genomic analysis to explore strain-specific traits.
C. ALLEN, F. Meng, J. M. Jacobs, L. Babujee Department of Plant Pathology, University of Wisconsin-Madison.
Phytopathology 99:S166.

Abstract: Most strains of the bacterial wilt pathogen Ralstonia solanacearum are tropical, but one group, Race 3 biovar 2 (R3b2), is adapted to cooler environments and causes disease in temperate zones and tropical highlands. We compared the growth and virulence of R. solanacearum strains GMI1000 (tropical, biovar 3) and UW551 (R3b2, temperate) at temperate and tropical temperatures. The two strains grew similarly in media at 20°C and 28°C. At 28°C, both strains wilted tomato plants rapidly in a naturalistic soil-soak virulence assay. In contrast, at 20°C UW551 was much more virulent on tomato than GMI1000, suggesting that interaction with plants is required for the temperate epidemiological trait of R3b2. To understand the mechanisms of R3bv2 cold tolerance, we studied global gene expression patterns of the two strains at 20°C and 28°C using genomic microarrays. In rich medium, the strains’ expression profiles differed significantly with respect to both strain and temperature. In the four conditions, we found differential expression of genes involved in cell wall/membrane synthesis and function, carbohydrate transport and metabolism, transcription, replication, recombination and repair, and diverse unknown functions, including some specific to R3bv2. A hitherto cryptic quorum sensing system, SolIR, and a SolIR-dependent gene, aidA, were up-regulated in R3bv2 at 20°C. aidA, which was expressed around 12-fold higher at 20°C, is not present in the GMI1000 genome.