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Genetic factors of Pseudomonas syringae pv. glycinea which enhance survival
Abstract
Various genetic factors of Pseudomonas syringae pv. glycinea were analyzed. Avirulence gene D (avrD) was characterized in seven races (0 through 6) of Pseudomonas syringae pv. glycinea. The predicted encoded proteins were similar to the functional class II allele from P. s. pv. phaseolicola G50 race 2; however, nine amino acid positions contained mutations. Although RFLP analysis for the P. s. pv. glycinea avrD genes hardly varied, upstream and downstream flanking regions varied considerably. The presence of avrD in all tested isolates indicates that they provide an important function in the bacteria, but have been modified to escape defense recognition by Rpg4-containing soybean plants. The dnaK gene from P. s. pv. glycinea PG4180 was cloned and sequenced. The dnaK coding region was 1,917 bp and contained the characteristic $\sigma\sp{32}$ heat shock promoter 91 bp upstream of the translational start site. The PG4180 dnaK gene complemented an E. coli dnaK mutant for growth at temperatures above 37$\sp\circ$C. All attempts to eliminate dnaK function in PG4180 failed. An anti-DnaK monoclonal antibody was used to monitor DnaK levels; in P. s. pv. glycinea race 4, DnaK production increased with cell growth at 26$\sp\circ$C. At 32 and 38$\sp\circ$C, DnaK levels increased transiently, and then decreased rapidly. Expression of dhaK in Pseudomonas syringae pv. glycinea PG4180 was investigated by constructing dnaK::uidA transcriptional fusions in pBBR.GUS. Glucuronidase activity in PG4180 cells containing the transcriptionally active dnaK::uidA fusion increased with growth when the cells were incubated at 28$\sp\circ$C. When cells were incubated at 18$\sp\circ$C, dnaK::uidA expression remained low. dnaK::uidA expression increased markedly when cells were preincubated at 18$\sp\circ$C for 24 h and then shifted to 35$\sp\circ$C. However, cell growth was inhibited at 35$\sp\circ$C, indicating the DnaK did not aid in the acclimation of PG4180 to supraoptimal temperatures. In contrast, the cfl promoter showed optimal expression at 18$\sp\circ$C and was repressed at 35$\sp\circ$C. These results are relevant to bacterial blight of soybeans, the disease incited by P. s. pv. glycinea, which flourishes in wet, cool weather.
Subject Area
Plant pathology|Microbiology
Recommended Citation
Keith, Lisa Marie, "Genetic factors of Pseudomonas syringae pv. glycinea which enhance survival" (1998). ETD collection for University of Nebraska-Lincoln. AAI9902966.
https://digitalcommons.unl.edu/dissertations/AAI9902966