The same results were obtained when the cells were incubated in nutrient-rich B media (data not shown). These results indicated clearly that the regulation of hrpB expression by prhK, prhL, and prhM is dependent on prhG but not on hrpG. We have reported previously that the expression of prhG is positively regulated by PhcA (Y. Zhang, unpublished data). To examine the influence of prhL and prhM on the expression of phcA, we constructed deletion mutants of RK5043 (phcA-lacZYA), which resulted in RK5270 (ΔprhL) and RK5268 (ΔprhM). The expression levels of phcA were PLX-4720 cell line similar in the wild type and the prhL and prhM mutants (Table 2). This suggests that prhL and prhM
are not involved in the regulation of phcA expression. We used a Tn7-based broad-range bacterial cloning and expression system for complementation (Choi et al., 2005). When we tested this system for complementation in the hrpG mutant, HrpG function was completely recovered (data not shown). However, when prhK (in pUC2171), prhL (in pUC2170), and prhM (in pUC2169) were transposed into their corresponding mutants, PLX3397 research buy the gene functions were not restored (Table 3), despite the fact that no polar effects were observed, and that the transgenes were under the control of their endogenous promoter. Even transforming RK5204 (ΔprhK) and RK5208 (ΔprhL) with two genes at once [prhK and prhL (in pUC7170)] did not complement these mutants (Table 3). Instead, all three genes, prhK, prhL, and prhM,
were required at once to complement the three mutants (Table 3). We conclude that the coordinate expression of the three genes is likely to be necessary GBA3 for the precise control of prhG expression. Based on the expression
profile of prhK operon (Y. Zhang, unpublished data), PrhM may play a role in this coordination, although the exact function of PrhM remains to be elucidated. The pathogenicity of the mutants was tested by soil-soak inoculation. The popA mutant causes wilt in tomato plants (Kanda et al., 2003b). Tomato plants inoculated at the roots with RK5050 (popA-lacZYA) became wilted within 5 days postinoculation (dpi) and died by 12 dpi (Fig. 2a). None of the RK5050 prhK, prhL, or prhM mutants caused wilt in tomato plants (Fig. 2a). When the petiole inoculation method was used, the same phenotypes were observed (data not shown). The other R. solanacearum strain RK10001 caused the tomato plants to wilt even earlier than RK5050 (Fig. 2b). Unlike tomato plants inoculated with the OE1-1 mutants, tomato plants inoculated with the RS1002 prhK, prhL, or prhM mutants wilted eventually. However, all three mutants were less virulent than the wild type (Fig. 2b). RK10001 and the three mutants based on this strain elicited an HR with similar symptoms (data not shown). Although the prhKLM mutants drastically reduced the expression of hrp regulon in both the OE1-1 and RS1002 mutants, the disease symptoms caused by pathogens with different genetic backgrounds showed large variation.