Sfa2 transcriptional regulator: a convergence node for fine tuning the expression of type III and VI secretion systems in Pseudomonas syringae pv. tomato DC3000    
C. CHIEN (1), Y. Lu (2), N. Lin (1) (1) Department of Agricultural Chemistry, National Taiwan University, Taiwan; (2) Department of Agricultural Chemistry, National Taiwan University, Malaysia

Pseudomonas syrinage pv. tomato (Pst), the causative agent of tomato speck disease, is comm used as a model to investigate plant-microbe interactions. It has been demonstrated that type three secretion system (T3SS) is required for its pathogenicity and virulence on tomato and Arabidopsis. In the absence of plant hosts, type six secretion system (T6SS) could contribute to adaptation and growth advantage against microbial competitors present in the same niches. In Pst DC3000, the expression of T3SS is induced by plant signals or conditions mimicking apoplastic fluid while that of T6SS is always detectable in a growth dependent manner. Although we observed that the expressions of T3SS and T6SS were regulated reciprocally, this regulation is irrelevant to the functions of sensor kinases RetS and LadS. To investigate whether and how T3SS and T6SS are co-regulated in Pst DC3000, we first examined hcp2 expression in Dsfa2 and DPSPTO_4453 (sigma 54) mutants, and found that both Sfa2 and PSPTO_4453 were required for hcp2 expression. Using a pathogenicity assay, we showed that deletion of PSPTO_4453 abolished Pst DC3000 ability to cause disease on tomato, but more bacterial growth was observed in tomato plants infected with Dsfa2. In contrast, fewer bacterial numbers was recovered in tomato plants inoculated with Dsfa2 overexpressing sfa2 on a plasmid. By means of semi-quantitative RT-PCR and real-time PCR, downregulation of hrpL and avrPto/avrPtoB was detected in Dsfa2. Taken together, through deciphering the role of Sfa2, we revealed that in Pst DC3000, T6SS itself encodes a transcription factor functioning as a convergence node to co-regulate the expression of T3SS and T6SS, probably via the interaction with PSPTO_4453.

Abstract Number: P6-138
Session Type: Poster