Impact of Paraburkholderia phytofirmans PsJN on Grapevine Phenolic Metabolism

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

Bacillus subtilis PTA-271 counteracts Botryosphaeria dieback in grapevine, triggering immune responses and detoxification of fungal phytotoxins

Plant pathogens have evolved various strategies to enter hosts and cause diseases. Particularly Neofusicoccum parvum, a member of Botryosphaeria dieback consortium, can secrete the phytotoxins (-)-terremutin and (R)-mellein during grapevine colonization. The contribution of phytotoxins to Botryosphaeria dieback symptoms still remains unknown. Moreover, there are currently no efficient control strategies of this disease, and agro-environmental concerns have raised increasing interest in biocontrol strategies to limit disease spread in vineyards, especially by using some promising beneficial bacteria. Here, we first examined in planta the biocontrol capacity of Bacillus subtilis PTA-271 against N. parvum Np-Bt67 strain producing both (-)- terremutin and (R)-mellein. We then focused on the direct effects of PTA-271 on pathogen growth and the fate of pure phytotoxins, and explored the capacity of PTA- 271 to induce or prime grapevine immunity upon pathogen infection or phytotoxin exposure. Results provided evidence that PTA-271 significantly protects grapevine cuttings against N. parvum and significantly primes the expression of PR2 (encoding a β-1,3-glucanase) and NCED2 (9-cis-epoxycarotenoid dioxygenase involved in abscisic acid biosynthesis) genes upon pathogen challenge. Using in vitro plantlets, we also showed that PTA-271 triggers the expression of salicylic acid- and jasmonic acid-responsive genes, including GST1 (encoding a glutathione-S-transferase) involved in detoxification process. However, in PTA-271-pretreated plantlets, exogenous (-)-terremutin strongly lowered the expression of most of upregulated genes, except GST1. Data also indicated that PTA-271 can detoxify both (-)- terremutin and (R)-mellein and antagonize N. parvum under in vitro conditions. Our findings highlight (-)-terremutin and (R)-mellein as key aggressive molecules produced by N. parvum that may weaken grapevine immunity to promote Botryosphaeria dieback symptoms. However, PTA-271 can efficiently attenuate Botryosphaeria dieback by enhancing some host immune responses and detoxifying both phytotoxins produced by N. parvum

Bacillus subtilis PTA-271 Counteracts Botryosphaeria Dieback in Grapevine, Triggering Immune Responses and Detoxification of Fungal Phytotoxins

Plant pathogens have evolved various strategies to enter hosts and cause diseases. Particularly Neofusicoccum parvum, a member of Botryosphaeria dieback consortium, can secrete the phytotoxins (-)-terremutin and (R)-mellein during grapevine colonization. The contribution of phytotoxins to Botryosphaeria dieback symptoms still remains unknown. Moreover, there are currently no efficient control strategies of this disease, and agro-environmental concerns have raised increasing interest in biocontrol strategies to limit disease spread in vineyards, especially by using some promising beneficial bacteria. Here, we first examined in planta the biocontrol capacity of Bacillus subtilis PTA-271 against N. parvum Np-Bt67 strain producing both (-)-terremutin and (R)-mellein. We then focused on the direct effects of PTA-271 on pathogen growth and the fate of pure phytotoxins, and explored the capacity of PTA-271 to induce or prime grapevine immunity upon pathogen infection or phytotoxin exposure. Results provided evidence that PTA-271 significantly protects grapevine cuttings against N. parvum and significantly primes the expression of PR2 (encoding a β-1,3-glucanase) and NCED2 (9-cis-epoxycarotenoid dioxygenase involved in abscisic acid biosynthesis) genes upon pathogen challenge. Using in vitro plantlets, we also showed that PTA-271 triggers the expression of salicylic acid- and jasmonic acid-responsive genes, including GST1 (encoding a glutathione-S-transferase) involved in detoxification process. However, in PTA-271-pretreated plantlets, exogenous (-)-terremutin strongly lowered the expression of most of upregulated genes, except GST1. Data also indicated that PTA-271 can detoxify both (-)-terremutin and (R)-mellein and antagonize N. parvum under in vitro conditions. Our findings highlight (-)-terremutin and (R)-mellein as key aggressive molecules produced by N. parvum that may weaken grapevine immunity to promote Botryosphaeria dieback symptoms. However, PTA-271 can efficiently attenuate Botryosphaeria dieback by enhancing some host immune responses and detoxifying both phytotoxins produced by N. parvum

Understand the Potential Role of Aureobasidium pullulans, a Resident Microorganism From Grapevine, to Prevent the Infection Caused by Diplodia seriata

Grapevine trunk diseases (GTDs) are one of the major concern amongst grapevine diseases, responsible for the decline of vineyards and for several economical losses. Since grapevine is naturally colonized by resident microorganisms such as Aureobasidium pullulans, the present challenge is to understand their biocontrol potential and how such microorganisms can be successfully integrated in the control of GTDs. In this context, the first priority consists to exploit the plant-beneficial-phytopathogen interactions in plant model systems, to identify the most prevalent equilibrium limiting expression of GTDs. In the current study, we deep characterized the interaction of a resident and abundant microorganism from grapevine – Aureobasidium pullulans strain Fito_F278 – against D. seriata F98.1, a Botryosphaeria dieback agent, and with plant (cv Chardonnay). Results revealed that A. pullulans strain Fito_F278 was able to reduce significantly the mycelium growth of D. seriata F98.1 at 33.41 ± 0.55%, under in vitro conditions, though this reduction is possibly dependent on a direct interaction between strain Fito_F278 and pathogen. Furthermore, strain Fito_F278 was able to promote an induction of some plant defense responses in cutting plants, 1 week after the D. seriata F98.1 infection. Results evidenced that strain Fito_F278 colonized efficiently grapevine at both epiphyte and endophyte level, could persist on plant roots for long-periods (up to 2 months after its inoculation) and grow at different pH and high salinity conditions. Moreover, a significant decrease of the microbial load from soil and rhizosphere was observed in plants treated with the strain Fito_F278, suggesting its competitivity potential in a microbial ecosystem. Altogether, the present study gives the first insights about the interaction of A. pullulans strain Fito_F278, a resident microorganism, with grapevine, its potential role against a Botryosphaeria dieback agent, and highlights its importance to toward more resilient grapevine

Burkholderia phytofirmans PsJN confers grapevine resistance against Botrytis cinerea via a direct antimicrobial effect combined with a better resource mobilization

Plant innate immunity serves as a surveillance system by providing the first line of powerful weapons to fight against pathogen attacks. Beneficial microorganisms and Microbial-Associated Molecular Patterns might act as signals to trigger this immunity. Burkholderia phytofirmans PsJN, a highly efficient plant beneficial endophytic bacterium, promotes growth in a wide variety of plants including grapevine. Further, the bacterium induces plant resistance against abiotic and biotic stresses. However, no study has deciphered triggered-mechanisms during the tripartite interaction between grapevine, B. phytofirmans PsJN and Botrytis cinerea. Herein, we showed that in contrast with classical rhizobacteria, which are restricted in the root system and act through ISR, B. phytofirmans PsJN is able to migrate until aerial part and forms at leaves surface a biofilm around B. cinerea mycelium to restrict the pathogen. Nevertheless, considering the endophytic level of PsJN in leaves, the plant protection efficacy of B. phytofirmans PsJN could not be explained solely by its direct antifungal effect. Deeper investigations showed a callose deposition, H2O2 production and primed expression of PR1, PR2, PR5 and JAZ only in bacterized-plantlets after pathogen challenge. The presence of PsJN modulated changes in leaf carbohydrate metabolism including gene expression, sugar levels and chlorophyll fluorescence imaging after Botrytis challenge. Our findings indicated that protection induced by B. phytofirmans PsJN was multifaceted and relied on a direct antifungal effect, priming of defense mechanisms as well as the mobilization of carbon sources in grapevine leaf tissues

Caractérisation du mode d’action des rhamnolipides dans la défense des plantes et l’induction d’une résistance contre des agents phytopathogènes biotrophes et nécrotrophes

National audienceLes rhamnolipides (RL) sont des glycolipides amphiphiles produits par différentes bactéries notamment du genre Pseudomonas et Burkholderia. Les RL comprennent généralement une chaîne d’acides gras couplée à un ou plusieurs rhamnoses. Il sont impliqués dans la formation de biofilms, dans la mobilité bactérienne et constituent, pour certaines bactéries, des facteurs de virulence (Vatsa et al. 2010). Nous avons montré que les RL sont perçus en tant qu’éliciteurs par les cellules de vigne et que cette reconnaissance provoque un influx de Ca2+, l’activation de plusieurs MAPK (Mitogen-Activated Protein Kinase), la production de formes actives de l’oxygène ainsi que l’expression d’une batterie de gènes de défense. Les RL permettent de protéger efficacement des vitroplants de vigne contre le champignon nécrotrophe Botrytis cinerea (Varnier et al. 2009). Les RL sont aussi capables de potentialiser les réponses de défense activées par d’autres éliciteurs, notamment issus de B. cinerea. Chez la plante modèle Arabidopsis thaliana, le prétraitement avec les RL active une résistance à l’oomycète biotrophe Hyaloperonospora arabidopsidis, à la bactérie hémibiotrophe Pseudomonas syringae pv. tomato ainsi qu’au champignon B. cinerea. En utilisant une approche mutant, nous avons démontré que la résistance induite par les RL implique des voies de signalisation différentes en fonction du type d’interaction (Sanchez et al. 2012). D’autre part, les RL ont une activité antimicrobienne directe sur les champignons ou les oomycètes. De manière plus générale, les RL sont reconnus pour leurs propriétés de biosurfactants et leur potentiel en bioremédiation. Ils sont aussi utilisés dans l’industrie alimentaire. Nos résultats suggèrent que ces molécules ont un potentiel important pour une utilisation en tant que SDN (stimulateur de défense naturel) dans le cadre de stratégies alternatives de lutte parasitaire chez la vigne. Sanchez L, Courteaux B, Hubert J, Kauffmann S, Renault JH, et al. (2012) Rhamnolipids Elicit Defense Responses and Induce Disease Resistance against Biotrophic, Hemibiotrophic, and Necrotrophic Pathogens That Require Different Signaling Pathways in Arabidopsis and Highlight a Central Role for Salicylic Acid. Plant Physiology 160: 1630-1641. Vatsa P, Sanchez L, Clément C, Baillieul F, Dorey S (2010) Rhamnolipid biosurfactants as new players in animal and plant defense against microbes. International Journal of Molecular Sciences 11: 5095-5108. Varnier AL, Sanchez L, Vatsa P, Boudesocque L, Garcia-Brugger A, et al. (2009) Bacterial rhamnolipids are novel MAMPs conferring resistance to Botrytis cinerea in grapevine. Plant, Cell & Environment 32: 178-193

Impacts of <em>Paraburkholderia phytofirmans</em> Strain PsJN on Tomato (<em>Lycopersicon esculentum</em> L.) Under High Temperature

Abnormal temperatures induce physiological and biochemical changes resulting in the loss of yield. The present study investigates the impact of the PsJN strain of Paraburkholderia phytofirmans on tomato (Lycopersicon esculentum Mill.) in response to heat stress (32°C). The results of this work showed that bacterial inoculation with P. phytofirmans strain PsJN increased tomato growth parameters such as chlorophyll content and gas exchange at both normal and high temperatures (25 and 32°C). At normal temperature (25°C), the rate of photosynthesis and the photosystem II activity increased with significant accumulations of sugars, total amino acids, proline, and malate in the bacterized tomato plants, demonstrating that the PsJN strain had a positive effect on plant growth. However, the amount of sucrose, total amino acids, proline, and malate were significantly affected in tomato leaves at 32°C compared to that at 25°C. Changes in photosynthesis and chlorophyll fluorescence showed that the bacterized tomato plants were well acclimated at 32°C. These results reinforce the current knowledge about the PsJN strain of P. phytofirmans and highlight in particular its ability to alleviate the harmful effects of high temperatures by stimulating the growth and tolerance of tomato plants

On a Cold Night: Transcriptomics of Grapevine Flower Unveils Signal Transduction and Impacted Metabolism

Low temperature is a critical environmental factor limiting plant productivity, especially in northern vineyards. To clarify the impact of this stress on grapevine flower, we used the Vitis array based on Roche-NimbleGen technology to investigate the gene expression of flowers submitted to a cold night. Our objectives were to identify modifications in the transcript levels after stress and during recovery. Consequently, our results confirmed some mechanisms known in grapes or other plants in response to cold stress, notably, (1) the pivotal role of calcium/calmodulin-mediated signaling; (2) the over-expression of sugar transporters and some genes involved in plant defense (especially in carbon metabolism), and (3) the down-regulation of genes encoding galactinol synthase (GOLS), pectate lyases, or polygalacturonases. We also identified some mechanisms not yet known to be involved in the response to cold stress, i.e., (1) the up-regulation of genes encoding G-type lectin S-receptor-like serine threonine-protein kinase, pathogen recognition receptor (PRR5), or heat-shock factors among others; (2) the down-regulation of Myeloblastosis (MYB)-related transcription factors and the Constans-like zinc finger family; and (3) the down-regulation of some genes encoding Pathogen-Related (PR)-proteins. Taken together, our results revealed interesting features and potentially valuable traits associated with stress responses in the grapevine flower. From a long-term perspective, our study provides useful starting points for future investigation

Le biocontrôle des stress biotiques et abiotiques chez le blé : c’est possible

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