Project description: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 pathogen or pest attacks. In ISR the defense arsenal in plants remains dormant and it is only triggered by the infection, allowing a rapid response and a better allocation of plant resources. We recently described that the well-known beneficial bacterium Paraburkholderia phytofirmans PsJN is able to reduce Arabidopsis thaliana susceptibility to Pseudomonas syringae Pst DC3000 through ISR. 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 the infection with Pst DC3000 strain. These data were used to perform a gene network analysis to identify highly connected transcription factors that may be acting as hubs in controlling this ISR response. Before the pathogen challenge, strain PsJN regulated 405 genes (corresponding to 1.5% of the analyzed genome). PsJN-inoculated plants presented a faster and stronger transcriptional response 1-hour post infection (hpi) compared with the non-inoculated plants, which presented the highest transcriptional changes 24 hpi. A principal component analysis showed that PsJN-induced plant responses to the pathogen could be differentiated from those induced by the sole pathogen. Forty-eight transcription factors were regulated by PsJN 1 hpi, and a system biology analysis revealed a network with 4 modules where LHY, WRKY28, MYB31 and RRTF1 are highly connected transcription factors, that can be acting as hub regulators in this interaction. These modules are related to Jasmonate, Ethylene, Salicylic acid and ROS pathways. Additionally, the down- and up-regulation of ANAC32 and ORA59, respectively, support an important role of PDF1.2. These results indicate that a rapid and specific response of PsJN-inoculated plants to this virulent pathogen could be the pivotal element in the protection mechanism. A role for specific transcriptional regulators in the orchestration of this complex molecular response is also proposed
Project description:Phenolic compounds are implied in plant-microorganisms interaction and may be induced in response to plant growth-promoting rhizobacteria (PGPRs). Among PGPR, the beneficial bacterium Paraburkholderia phytofirmans PsJN was previously described to stimulate the growth of plants and to induce a better adaptation to both abiotic and biotic stresses. This study aimed to investigate the impact of PsJN on grapevine secondary metabolism. For this purpose, gene expression (qRT-PCR) and profiling of plant secondary metabolites (UHPLC-UV/DAD-MS QTOF) from both grapevine root and leaves were compared between non-bacterized and PsJN-bacterized grapevine plantlets. Our results showed that PsJN induced locally (roots) and systemically (leaves) an overexpression of PAL and STS and specifically in leaves the overexpression of all the genes implied in phenylpropanoid and flavonoid pathways. Moreover, the metabolomic approach revealed that relative amounts of 32 and 17 compounds in roots and leaves, respectively, were significantly modified by PsJN. Once identified to be accumulated in response to PsJN by the metabolomic approach, antifungal properties of purified molecules were validated in vitro for their antifungal effect on Botrytis cinerea spore germination. Taking together, our findings on the impact of PsJN on phenolic metabolism allowed us to identify a supplementary biocontrol mechanism developed by this PGPR to induce plant resistance against pathogens.
Project description:Grapevine flowering is an important stage in the epidemiology of Botrytis cinerea, the causal agent of gray mold disease. To prevent infection and to minimize postharvest losses, the control of this necrotrophic fungus is mainly based on chemical fungicides application. However, there is a growing interest in other control alternatives. Among them, the use of beneficial microorganisms appears as an eco-friendly strategy. This study aims to investigate the effect of Paraburkholderia phytofirmans PsJN, root-inoculated or directly sprayed on fruiting cuttings inflorescences to control B. cinerea growth. For this purpose, quantification by real time PCR of Botrytis development, direct effect of PsJN on fungal spore germination and chemotaxis were assayed. Our results showed a significant protective effect of PsJN only by direct spraying on inflorescences. Moreover, we demonstrated an inhibition exerted by PsJN on Botrytis spore germination, effective when there was a direct contact between the two microorganisms. This study showed that PsJN is positively attracted by the pathogenic fungus B. cinerea and forms a biofilm around the fungal hyphae in liquid co-culture. Finally, microscopic observations on fruit cuttings revealed a co-localization of both beneficial and pathogenic microorganisms on grapevine receptacle and stigma that might be correlated with the protective effect induced by PsJN against B. cinerea via a direct antimicrobial effect. Taking together, our findings allowed us to propose PsJN as a biofungicide to control grapevine gray mold disease.
Project description: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.