Pathogen-Induced Defense Signaling and Signal Crosstalk in Arabidopsis

............................................................................................................................................. 8 INTRODUCTION.................................................................................................................................... 9 PLANT-PATHOGEN INTERACTION .........................................................................................................11 PHYTOPATHOGENIC BACTERIA.............................................................................................................12 PLANT DEFENSE ...................................................................................................................................13 Preformed defenses ........................................................................................................................13 Inducible defenses ..........................................................................................................................14 Elicitation of plant defense........................................................................................................................... 15 General elicitors ...................................................................................................................................... 15 Race-specific elicitors ............................................................................................................................. 16 Elicitor perception ................................................................................................................................... 17 Defense signaling ......................................................................................................................................... 18 Role of reactive oxygen species in defense signaling............................................................................. 20 Role of nitric oxide in defense signaling ................................................................................................ 22 Salicylic acid-mediated defense signaling .............................................................................................. 22 Nature of the systemic signal............................................................................................................. 25 Jasmonic acid-mediated defense signaling ............................................................................................. 26 Jasmonic acid in systemic signaling .................................................................................................. 27 Ethylene-mediated defense signaling...................................................................................................... 28 Abscisic acid................................................................................................................................................. 30 Role of ABA in abiotic stress responses................................................................................................. 31 Role of ABA in biotic stress responses................................................................................................... 33 CROSSTALK BETWEEN SIGNALING PATHWAYS .....................................................................................35 MODEL ORGANISM ERWINIA CAROTOVORA ............................................................................................37 OPEN QUESTIONS .................................................................................................................................39 AIMS OF THE STUDY.........................................................................................................................40 MATERIALS AND METHODS...........................................................................................................41 RESULTS AND DISCUSSION ............................................................................................................ 42 ERWINIA CAROTOVORA AND ELICITORS HRPN AND PEHA TRIGGER DISTINCT BUT INTERACTING DEFENSE RESPONSES AND CELL DEATH IN ARABIDOPSIS (I) ..................................................................42 HrpN elicits lesion formation and induces resistance to E. carotovora in Arabidopsis .................42 Establishment of HrpN-triggered resistance requires both SA and JA signaling ...........................43 Synergistic action of elicitors HrpN and PehA triggers enhanced defense gene expression and cell death.........................................................................................................................................44 PLANT RESPONSES TO E. CAROTOVORA (II, III) .....................................................................................44 CHLOROPHYLLASE 1 AFFECTS INDUCTION OF DEFENSE PATHWAYS IN PLANTS (II) .............................. 45 RNAi silencing of chlorophyllase 1 (AtCLH1) improves resistance to E. carotovora in Arabidopsis .................................................................................................................................... 45 Resistance of AtCLH1 RNAi-silenced plants is light-dependent and involves increased accumulation of ROS ..................................................................................................................... 46 Silencing of AtCLH1 affects the balance between SAand JA-dependent defenses in Arabidopsis ................................................................................................................................. 47 ERD15 IS A NEGATIVE REGULATOR OF ABA RESPONSES IN ARABIDOPSIS (III) .................................... 49 ERD15 is rapidly induced by both biotic and abiotic factors ......................................................... 49 Modulation of ERD15 expression affects abiotic stress tolerance by influencing ABA sensitivity ...................................................................................................................................... 49 Insensitivity to ABA enhances resistance of Arabidopsis to E. carotovora................................... 51 ERD15 is a negative regulator of ABA responses in Arabidopsis ................................................. 52 CONCLUDING REMARKS AND FUTURE PERSPECTIVES ...................................................... 53 ACKNOWLEDGMENTS ..................................................................................................................... 56 REFERENCES ...................................................................................................................................... 58