Pantoea eucalyptii INDUCES SYSTEMIC RESISTANCE IN Arabidopsis thaliana AGAINST Botrytis cinerea BY PRIMING DEFENSE RESPONSES

ROMERO, FERNANDO MATIAS; MARINA, MARÍA; ROSSI, FRANCO RUBÉN; VIAUD, MURIEL; PIECKENSTAIN, FERNANDO LUIS

Santa Cruz

Simposio; XVII International Botrytis Symposium; 2016

Universidad de Chile

Many endophytic bacteria colonize host tissues internally without causing damage or eliciting disease symptoms. Some of them also promote plant growth. Previously, we obtained a collection of bacterial endophytes from leaves of field-grown tomato and identified strains capable to systemically protect this plant against B. cinerea infection. In the present work we used the model plant A. thaliana to analyze the mechanisms involved in the induction of systemic resistance to B. cinerea by one of these strains, Pantoea eucalypti NT6 (PeNT6). In order to evaluate if PeNT6 triggers induced systemic resistance (ISR) in A. thaliana, plants were soil-inoculated with this bacterium and challenged by leaf inoculation with B. cinerea four weeks later. PeNT6 inoculation reduced (30-60%) the size of necrotic lesions caused by B. cinerea. Inoculation with PeNT6 had no effect on the expression of the defense-related genes PR1, PDF1.2, MPK3 and WRKY33. However, plants inoculated with PeNT6 and further challenged with B. cinerea exhibited higher levels of MPK3 and WRKY33 expression than those plants challenged with B. cinerea without previous inoculation with the bacterium. NT6 was unable to trigger ISR in A. thaliana mutants affected in defense signaling pathways mediated by jasmonic acid (coi1), ethylene (ein2) and salicylic acid (sid2). However, the npr1 mutant showed an ISR similar to the wild type. Mutants in MPK3 and MPK6 showed a differential response. While the mpk3 mutant showed no induction of resistance, the mpk6 showed a similar level of ISR to wild type plants. ISR triggered by PeNT6 also involved priming of callose deposition upon Botrytis infection. Finally, the use of a GFP-labeled B. cinerea strain allowed us to determine that in planta germination of fungal conidia was retarded in NT6-inoculated plants. Results hereby presented demonstrate that P. eucalypti triggers ISR to B. cinerea by priming specific components of the defense machinery, such as the kinase MPK3 and the transcription factor WRKY33. ISR triggered by NT6 was also found to depend on jasmonic acid, ethylene and salicylic acid signaling pathways, but did not depend on the regulatory protein NPR1. The kinase MPK3 was also found to play a key role in the onset of ISR by PeNT6. These findings contribute to understand the mechanisms underlying ISR to B. cinerea provided by plant inoculation with beneficial bacteria with the potential to be used as biological control agents.