| Ethylene response factors (ERFs) bind to the cis element GCC box that is present in the promoter region of many pathogen-related ( PR) genes. A large number of ERF genes are pathogen inducible, suggesting an important role of ERFs in plant-pathogen interactions. The tomato ERF gene Pti5 product interacts with the resistance protein Pto kinase. Overexpression of Pti5 or Pti5-VP16, a translational fusion with a constitutive transcriptional activation domain, in tomato enhanced resistance to Pseudomonas syringae pv. tomato. Constitutive expression of Pti5 or Pti5-VP16 did not affect the basal level of PR gene expression, but it accelerated pathogen-induced expression of GluB and Catalase. The results demonstrate a positive role of Pti5 in defense gene regulation and disease resistance, and suggest that a pathogen-activated post-transcriptional regulatory step is necessary for the pathogen-induction of the defense gene expression.; Not all ERF genes function in resistance to the bacterial pathogen. We found that the expression of an Arabidopsis ERF gene, RAP2.6, was closely associated with Pseudomonas syringae pathogenicity and plant susceptibility. A highly sensitive promoter-reporter line was developed by fusing the RAP2.6 promoter with a firefly luciferase gene LUC (RAP2.6-LUC ). Bacterial mutants hrcC, ΔCEL, and COR− that are either abolished in pathogenicity or reduced in virulence were largely defective in RAP2.6 promoter activation. We also show that the RAP2.6 promoter was a sensitive indicator for the activity of at least five individual bacterial effectors, AvrB, AvrRpt2, AvrPphB, HopPtoK, and AvrPphEPto. The presence of avrB, avrRpt2, and avrPphB in P. syringae pv. tomato DC3000 accelerated the RAP2.6 promoter induction. At least the avrB-mediated RAP2.6 activation was independent of R gene recognition. Conversely, the P. syringae pv. tomato DC3000 strain carrying a mutation in hopPtoK or avrPphE Pto was significantly reduced in RAP2.6-inducibility. These establish the RAP2.6-LUC reporter line as an ideal tool for the study of early activities of bacterial virulence factors.; Our studies support the idea that some ERF genes function positively to activate plant defense, whereas others may be actively manipulated by bacterial pathogens to promote parasitism. The latter can be used as an excellent tool to understand bacterial pathogenesis. |
