|GABRIEL, D. W.|
|NORMAN, D. J.|
Submitted to: International Congress on Molecular Plant-Microbe Interactions
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2007
Publication Date: N/A
Technical Abstract: Ralstonia solanacearum race 3 biovar 2 (R3B2) strains are one of only 10 USDA Select Agents, a category of quarantined pathogens reserved for the most serious threats to U.S. plant industry. The threat of R3B2 strains was not considered to be likely due to race (these are poorly defined) or biovar (utilization of three sugar alcohols), but rather ability to survive cold temperatures. R3B2 strains are distributed in the coldest areas of the world where R. solanacearum is found and are therefore thought to be cold tolerant, but there is little direct experimental data to support this assumption. More importantly, R3B2 strains do not even appear to be the most cold tolerant strains of the species. In this study, a freeze-thaw assay was developed that revealed that the survival of R3B2 strain UW551 is >100X higher than that of race 1 biovar 3 strain GMI1000 (Salanoubat, 2002). All R3B2 strains tested and some R1B1 strains, including P446 and P673 were more cold tolerant than some R3B2 strains by this assay. The 8X draft UW551 genome (http://vision.biotech.ufl.edu; Gabriel et al., 2005) was compared with the published genome of GMI1000, and no unusual pathogenicity factors were discovered. One putative UW551 cold shock gene, cspD3, was significantly larger than homologs in GMI1000 and three other less cold tolerant strains. Long versions of cspD3 were found conserved in the cold tolerant R1B1 strains. Cloned cspD3 from UW551 and from P446, each with their own promoters, conferred increased cold tolerance to both E. coli and to GMI1000. Cold tolerance genes, not race or biovar determining genes, should serve as the basis for quarantine regulations.