Abstract
Plant defense responses to biotic stresses are complex biological processes, all governed by sophisticated molecular regulations. Induced systemic resistance (ISR) is one of these defense mechanisms where beneficial bacteria or fungi prime plants to resist pathogens or pest attacks. In ISR, the defense arsenal in plants remains dormant and it is only triggered by an infection, allowing a better allocation of plant resources. Our group recently described that the well-known beneficial bacterium Paraburkholderia phytofirmans PsJN is able to induce Arabidopsis thaliana resistance to Pseudomonas syringae pv. tomato (Pst) DC3000 through ISR, and that ethylene, jasmonate and salicylic acid are involved in this protection. Nevertheless, the molecular networks governing this beneficial interaction remain unknown. To tackle this issue, we analyzed the temporal changes in the transcriptome of PsJN-inoculated plants before and after being infected with Pst DC3000. These data were used to perform a gene network analysis to identify highly connected transcription factors. Before the pathogen challenge, the strain PsJN regulated 405 genes (corresponding to 1.8% of the analyzed genome). PsJN-inoculated plants presented a faster and stronger transcriptional response at 1-hour post infection (hpi) compared with the non-inoculated plants, which presented the highest transcriptional changes at 24 hpi. A principal component analysis showed that PsJN-induced plant responses to the pathogen could be differentiated from those induced by the pathogen itself. Forty-eight transcription factors were regulated by PsJN at 1 hpi, and a system biology analysis revealed a network with four clusters. Within these clusters LHY, WRKY28, MYB31 and RRTF1 are highly connected transcription factors, which could act as hub regulators in this interaction. Concordantly with our previous results, these clusters are related to jasmonate, ethylene, salicylic, acid and ROS pathways. These results indicate that a rapid and specific response of PsJN-inoculated plants to the virulent DC3000 strain could be the pivotal element in the protection mechanism.
Highlights
Plants face a myriad of pathogens and pests in their natural environment resulting in tremendous annual crop losses worldwide, ranging from 20 to 40% of potential crop yield [1,2]
We recently reported that P. phytofirmans PsJN reduces disease susceptibility in Arabidopsis thaliana plants to the virulent strain Pseudomonas syringae pv tomato (Pst) DC3000, through the activation of Induced systemic resistance (ISR), by means of salicylic acid (SA), jasmonic acid (JA) and ET dependent signaling pathways [41]
To get a better understanding of the molecular changes underlying the ISR triggered by strain PsJN in Arabidopsis plants infected with a virulent bacterium, a transcriptome-profiling assay using non-inoculated plants and strain PsJN-inoculated (0 hpi) plants was performed
Summary
Plants face a myriad of pathogens and pests in their natural environment resulting in tremendous annual crop losses worldwide, ranging from 20 to 40% of potential crop yield [1,2]. In the context of a growing human population, elucidating the mechanisms of plant defense has become extremely important. Plant defense responses to biotic stresses are complex biological processes, involving numerous changes at the biochemical, physiological, and molecular (transcriptional) level, all governed by an intricate grid of hierarchical and regulatory interactions [4]. These defense mechanisms are triggered partly by the hormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) [5,6,7,8,9,10]. SA is involved in resistance against biotrophic pathogens [11], while JA and ET participate in the regulation of defense response against necrotrophic pathogens and insects [12,13]
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