QUORUM SENSING IN THE PLANT PATHOGEN ERWINIA CAROTOVORA SUBSP

___________________________________________________________________7 A. INTRODUCTION _____________________________________________________________9 1. Plant pathogens ____________________________________________________________________9 2. The soft-rot pathogen Erwinia (Pectobacterium) _________________________________________9 3. Virulence determinants of Erwinia carotovora subsp. ____________________________________11 3.1. Plant cell wall -degrading enzymes __________________________________________________________ 11 3.2. Secretion systems ________________________________________________________________________ 13 3.2.1. The type III secretion system and effector proteins__________________________________________ 13 3.3. Other virulence determinants _______________________________________________________________ 14 3.3.1. Motility ____________________________________________________________________________ 14 3.3.2. Siderophores and tolerance to oxidative stress _____________________________________________ 14 4. Virulence regulation in Ecc _________________________________________________________15 4.1. Global activators and repressors_____________________________________________________________ 15 4.2. Two-component signal transduction systems __________________________________________________ 18 5. Cell-to-cell communication by quorum sensing _________________________________________20 5.1. The AHSL signaling molecule and LuxI-type proteins___________________________________________ 21 5.2. LuxR-type proteins _______________________________________________________________________ 23 5.2.1. Mechanism of action__________________________________________________________________ 24 5.3. Quorum sensing in the plant pathogen Erwinia carotovora subsp. _________________________________ 26 5.3.1. Quorum sensing regulators of Ecc _______________________________________________________ 26 5.3.2. Quorum sensing controls a wide variety of functions ________________________________________ 27 5.3.3. Cross-talk between quorum sensing and the regulatory network _______________________________ 28 5.4. Quorum quenching _______________________________________________________________________ 29 B. AIMS OF THE STUDY________________________________________________________30 C. MATERIALS AND METHODS _________________________________________________31 D. RESULTS AND DISCUSSION _________________________________________________34 1. The acyl side chain of AHSLs defines the specificity of the communication system____________34 1.1. Specificity of AHSL sensing in Ecc__________________________________________________________ 34 1.2. Identification of critical residues in the AHSL synthase that determine acyl side chain length ___________ 35 1.3. Mutations causing changes in bacterial communication __________________________________________ 36 2. ExpR1 and ExpR2 control virulence and quorum sensing specificity _______________________37 2.1. ExpR1 and ExpR2 act as negative regulators of virulence ________________________________________ 37 2.2. ExpR1 and ExpR2 bind AHSL and determine the AHSL sensing specificity of Ecc ___________________ 38 2.3. ExpR1 and ExpR2 control RsmA, a global negative regulator of virulence __________________________ 39 2.4. ExpR1 changes the communication language __________________________________________________ 40 3. Identification of new quorum sensing targets in Ecc_____________________________________41 3.1. Identification of a plant ferredoxin-like protein and the regulator Hor as quorum sensing targets _________ 41 3.2. ExpR1 and ExpR2 control the expression of ferE and hor via RsmA _______________________________ 42 3.3. Contribution of Hor and FerE to virulence ____________________________________________________ 43 3.4. Quorum sensing regulate oxidative stress tolerance _____________________________________________ 44 E. CONCLUDING REMARKS AND FUTURE PERSPECTIVES _______________________45 F. ACKNOWLEDGEMENTS _____________________________________________________48 G. REFERENCES ______________________________________________________________50