Mauch-Mani, Brigitte

2018, Ben Rejeb, Ines, Mauch-Mani, Brigitte

La tomate compte parmi les légumes-fruits les plus importants sur le plan économique dans plusieurs pays. Cependant la sécheresse, la salinité et le les pathogènes constituent les principales causes de réduction et de variabilité des rendements des cultures. Bien que les plantes aient développé des capacités défensives contre ces stress, leur tolérance et résistance dépend du degré et de l’intensité du stress et aussi de l’espèce. Dans cette thèse, nous avons étudié le rôle de l’acide β-aminobutyrique (BABA) dans l’induction de la résistance contre le stress hydrique, le stress salin et la combinaison de salinité et infection avec Botrytis cinerea chez deux cultivars de tomate (cv Marmande : un cultivar résistant au stress et cv Cœur de Bœuf : un cultivar sensible au stress). Nos résultats ont montré que BABA atténue considérablement les effets nocifs d’un seul stress et aussi des stress combinés. Les plants de tomate sous contrainte hydrique ou saline, traités avec BABA accumulent plus de chlorophylle a et b, anthocyanine, ABA et montrent aussi une induction des gènes reliés au stress abiotique comparé aux plants non-traités. Nous avons trouvé une réduction des espèces réactives d’oxygène qui sont liées à une augmentation des antioxydants plus importante chez les plants traités avec BABA par rapport aux plants non-traités. Ce qui nous a surpris c’est que BABA induit plus de tolérance au cv Marmande qu’au cv Cœur de Bœuf. De plus, les plants traités avec BABA présentent une meilleure résistance contre la combinaison des deux stress par rapport aux plants non-traités suite à l’induction de l’accumulation de callose, d’H₂O₂, d’ABA, de SA et aussi l’expression de PR1 et PR5. Ceci ouvre de nombreuses perspectives quant à l’effet de BABA sur les métabolites., Tomatoes are among the most produced and consumed vegetable-fruit in many countries and is considered an economically important crop. However, drought, salinity and pathogen infection are the main causes of crop yield reduction and variability. Although plants have developed defensive capacities against these stresses, but plant tolerance and resistance depend on the degree and intensity of stress and on the species. In this thesis, we investigated the role of β-aminobutyric acid (BABA) in the induction of tolerance and resistance against drought stress, salt stress and combination of salinity and infection with Botrytis cinerea in two tomato cultivars (cv Marmande: a stress-resistant cultivar and cv Coeur de Boeuf: a stress-sensitive cultivar). Our results showed that BABA significantly reduces the harmful effects of a single and combined stress. Treated tomato plants with BABA in response to drought or salt stress accumulate more chlorophyll a and b, anthocyanin, ABA and genes related to abiotic stress compared to non-treated plants. We found a reduction in reactive oxygen species that are related to greater increase of antioxidant in treated-plants with BABA compared to non-treated ones. What surprised us is that BABA induces more tolerance to Marmande than to Coeur de Boeuf. In addition, plants treated with BABA show better resistance against the combination of both stresses compared to non-treated plants by induction of callose accumulation, H₂O₂, ABA, SA and the expression of PR1 and PR5. This opens many perspectives on the effect of BABA on metabolic study.

2013, Planchamp, Chantal, Mauch-Mani, Brigitte

To protect themselves against biotic and abiotic stresses, plants have developed a broad range of defense mechanisms that are constitutively present or that can be induced in response to a stress. Such induced defense can be the result of a resistance elicitation by non-pathogenic organisms that are present in soil and is then called induced systemic resistance (ISR). ISR confers plant resistance against a large variety of attackers such as pathogens and herbivores. In monocotyledonous plants this phenomenon has been less studied than in dicots such as Arabidopsis. Hence, the aim of this thesis was to enhance our knowledge on ISR in monocots and more specifically in maize plants.
To facilitate plant root manipulation for our experiments, we established a soil-free system for growing maize plants. Based on an existing system for root observation, we adapted a system that is convenient for working with beneficial as well as pathogenic microbes.
ISR establishment necessitates the local recognition of the beneficial microbe by the plant. Thus, we studied the reaction of maize after inoculation with a well-known maize colonizer rhizobacterium Pseudomonas putida KT2440. The presence of these bacteria activated plant immunity early in the interaction. We hypothesized that KT2440 manipulates root defense to be able to colonize roots. We observed that KT2440 had a beneficial effect on plant growth, showing their capacity to be a plant growth promoting rhizobacteria.
After analyzing the local plant response to KT2440 inoculation we tested the efficiency of KT2440 to induce a systemic defense against various types of attacks. We demonstrated that ISR triggered by KT2440 was efficient against an hemibiotrophic fungus, Colletotrichum graminicola, and a generalist herbivore, Spodoptera littoralis. However, the efficacy of ISR induced by KT2440 was dependent of the host-plant specialization of the leaf herbivores as ISR triggered by KT2440 did not affect the specialist S. frugiperda. Our transcript and metabolite analyses revealed the involvement of phenolic compounds as well as ethylene-dependent signaling in maize ISR. However, mechanisms involved in ISR induced by KT2440 in maize remain to be further investigated.

2011, Thuerig, Barbara, Slaughter, Ana R., Marouf, Elaheh, Held, Matthias, Mauch-Mani, Brigitte, Tamm, Lucius

The influence of site on resistance of grapevine (cv. Chasselas) to Plasmopara viticola was evaluated. Grapevine leaves from three vineyards in the region of Lake Neuchâtel (Switzerland) were tested for their susceptibility to P. viticola in the lab in five successive years (2004–2008), and the expression levels of four selected defence-related genes (Glucanase, Lipoxygenase 9, 9-cis epoxycarotenoid dioxygenase, Stilbene synthase) were studied in 1 year. In all 5 years of examination, differences between sites were substantial. In four out of 5 years, plants from site Hauvernier were much less susceptible to P. viticola than plants from site Auvernier. In another year, differences were less pronounced but still significant for one leaf age. Susceptibility of plants from a third site (Concise) varied from year to year. Differences in the genetic background were excluded by microsatellite analysis. Differences in susceptibility were mirrored in the constitutive expression pattern of four defence-related genes, with samples from the Hauterive site clearly separated from samples of the other two sites in redundancy analysis. Furthermore, it was evaluated whether site-specific resistance can be modulated by agronomic practices such as the application of organic amendments. In two commercial vineyards (cv. Pinot noir), soils had either not (control) or yearly (compost) been amended with a compost for the last 9 years. Leaves from plants grown in any of the two treatments did not differ in their susceptibility to P. viticola in both years of examination. Additionally, under controlled conditions, none of 19 different composts amended to the substrate of grapevine seedlings or cuttings affected their susceptibility to P. viticola, but 8 out of 19 composts reduced severity in the control bioassay Arabidopsis thaliana—Hyaloperonospora arabidopsidis, indicating that a modulation of site-specific susceptibility of grapevine plants by organic amendments is at the very least, difficult.

2010, Boachon, Benoît, Mauch-Mani, Brigitte

Dans la nature les plantes sont soumises à de nombreuses attaques de l’environnement tel que stress biotiques (Insectes, microorganismes pathogènes…) et abiotiques (Sècheresse, froid…). Cependant les plantes disposent de mécanismes de défenses naturelles complexes. En agriculture, malgré les efforts des sélectionneurs pour obtenir des variétés de plantes cultivées résistantes, les pertes de récoltes dues aux agents pathogènes restent très importantes. Les agriculteurs protègent leurs cultures à l’aide de produits phytosanitaires non sans soulever de nombreux problèmes sanitaires et environnementaux. Certaines molécules, appelées éliciteurs permettent de stimuler les défenses des plantes tandis que les agents primant tel que le BABA (acide β-aminobutyrique) permettent aux plantes de se préparer à mieux se protégèrent en cas d’attaques. La caractérisation des mécanismes de défenses des plantes ainsi que des mécanismes de virulence des pathogènes représente un enjeu important afin d’aborder la protection des plantes sous un autre angle.
Le but de ce travail de thèse a été d’aborder la recherche en phytopathologie moléculaire et les interactions plantes/pathogènes. Dans un premier temps, des outils de biologie moléculaire basés sur les réactions de polymérase en chaine en temps réel ont été développés afin de mesurer chez la plante modèle Arabidopsis thaliana la croissance de plusieurs microorganismes pathogènes ainsi que de mesurer les réponses de défense des plantes. Dans un deuxième temps ces méthodes ont été mises à contribution afin de disséquer les interactions de signalisation hormonale s’établissant lors de l’infection d’Arabidopsis par la bactérie pathogène Pseudomonas syringae. Les résultats obtenus permettent de mieux comprendre comment les bactéries, par le biais de leurs mécanismes de virulence, réduisent la mise en place des défenses naturelles des plantes par un jeu complexe de signalisation hormonale. Cette stratégie de virulence bactérienne peut être contournée en préparant les plantes à mieux se défendre avec l’utilisation d’agents primant tel que le BABA qui permet de rétablir les défenses naturelles des plantes en cas d’attaques.

2017, Martin, Charlotte, Mauch-Mani, Brigitte, Mascher, Fabio

La fusariose de l’épi est une des principales maladies des céréales, causée par les pathogènes du genre Fusarium. Elle engendre des pertes de rendement conséquentes ainsi que la contamination des grains en mycotoxines. Nocives pour la santé humaine et animale, ces toxines représentent une menace reconnue pour la sécurité alimentaire. L’utilisation de variétés résistantes permet de réduire considérablement les épidémies de fusariose. Dans toutes les céréales, cette résistance est cependant un caractère complexe et difficile à sélectionner. Il faut pour cela disposer à la fois d’une évaluation détaillée de l’impact de l’infection sur la plante, et d’une connaissance parfaite des mécanismes de résistance. Or, l’étude de la fusariose et de la résistance s’est principalement concentrée sur le blé, au détriment des autres céréales. Pour l’avoine particulièrement, la fusariose a été négligée longtemps et l’amélioration de la résistance est devenue une priorité pour lutter contre le nouveau risque sanitaire lié aux toxines de F.poae et F.langsethiae. Les travaux de sélection s’intéressent également de près aux composés bénéfiques pour la santé (CBS) présent dans les grains. En effet, les grains de blé contiennent des antioxydants dont les anthocyanes et les grains d’orge et d’avoine sont des sources reconnues de β-glucanes. Or, plusieurs CBS ont montré qu’ils pouvaient inhiber la croissance et la production de toxines des Fusarium en conditions in vitro, laissant ainsi suggérer qu’ils pourraient contribuer à la résistance contre la fusariose in planta.
L’objectif de cette thèse est de comprendre comment les grains de blé, d’orge et d’avoine se protègent contre les Fusarium. Le rôle des CBS dans la résistance des grains est étudié. Une première étude préliminaire nous a permis de comprendre les variations d’agressivité des pathogènes Fusarium au sein d’une population. Nous avons démontré que l’agressivité est liée au chémotype de la souche, est surtout conditionnée par l’environnement, mais n’est pas impactée par la résistance de l’hôte. Ces observations ont été essentielles pour la mise en place des infections artificielles au champ, ainsi qu’à l’aide à l’interprétation des résultats dans les essais suivants. Une deuxième étude nous a confirmé que les CBS peuvent contribuer in vivo à la résistance in vivo contre la fusariose. Nous avons en effet observé qu’au sein d’un large panel de variétés de blé, les plus résistantes contenaient, dans leurs épillets, les teneurs les plus élevées en acide férulique, principal antioxydant des céréales. Suite à ces résultats, les impacts de la fusariose, les éléments de résistance et la contribution de différents CBS ont été successivement étudiés dans les grains de blé, d’orge et d’avoine. Nous avons observé que le grain de blé possédait la résistance la plus complète pour lutter contre tous les dégâts que la fusariose peut causer, de la malformation des grains à l’accumulation de toxine deoxynivalénol (DON) produit par F.graminearum. Nous avons démontré qu’il peut également se prémunir contre la dégradation de ses composants, de sa qualité et de ses activités de synthèse. Les infections de F.graminearum dans le grain d’orge provoquent en plus d’une contamination en DON, des dégradations de la structure et de la composition du grain, notées entres autres par des réductions des teneurs en β-glucanes. Le grain d’orge possède des éléments de résistance distincts pour lutter indépendamment contre l’infection et contre l’accumulation en toxines. L’infection du grain d’avoine par F.poae et F.langsethiae a conduit à des contaminations en toxines, parfois sévères, sans causer aucun autre dégât ou symptôme. En comparaison avec le blé et l’orge, l’avoine possède un faible niveau de résistance contre ces contaminations. De plus, nos résultats suggèrent que la résistance d’une variété d’avoine dépend de la toxine en présence.
Le rôle des CBS dans la résistance des grains dépend du composé. Nos résultats montrent que les teneurs élevées en β-glucanes réduisent l’accumulation de toxines dans les grains d’orge, alors que les anthocyanes du grain de blé n’influencent pas la résistance. Dans le grain d’avoine, les contaminations en toxines ne sont pas modulée par les teneurs en β-glucanes, des augmentations de ces teneurs ont cependant été observées dans les grains les moins contaminés en toxine nivalénol.
En conclusion, les grains de blé, d’orge et d’avoine se protègent différemment contre la fusariose. La stabilité et l’héritabilité de la résistance est la plus élevée dans le blé, ce qui laisse présager d’un plus fort gain génétique dans la sélection de la résistance dans cette céréale que dans l’orge ou l’avoine. Par ailleurs nous avons démontré que si certains CBS intervenaient dans la résistance, augmenter leurs teneurs dans les grains ne permettra pas de limiter de façon significative les dégâts causés par la fusariose. Cela permettrait cependant le développement nouvelles variétés à la fois plus bénéfiques pour la santé et résistantes aux toxines., Fusarium head blight FHB is one of the main cereal disease. FHB is caused by the complex of Fusarium pathogens and results in significant yield losses and contamination of grain with mycotoxins. These toxins constitute a substantial risk to human health and a threat for food safety. The most dominant toxin is deoxynivalenol (DON), produced by F.gramineraum. The use of resistant varieties is the most sustainable way to control disease outbreaks and damages. In all cereals, resistance is a complex character, based on cumulative effects of many elements and so, difficult to select. An accurate assessment of all the impacts of Fusarium infection on plants and a perfect knowledge of resistance mechanisms are both necessary to breed resistant varieties. Yet, previous resistance studies of FHB and of resistance elements were mainly focused on wheat. For oats in particular, FHB is an emerging issue, and efficient resistance is now required to face the increasing occurrence of F.poae and F.langsethiae and their highly noxious toxins. Besides FHB resistance, breeding programs are now focusing more and more on nutritional values and the increase of Health Promoting Compounds HPC in cereal grains. Indeed, wheat grains can contain high amounts of antioxidants including anthocyanin compounds, barley and oat grains are sources of β-glucan. Interestingly, several cereal endogenous HPCs shown inhibitive effects on Fusarium growth and toxin synthesis in vitro conditions, hence suggesting they could contribute to FHB resistance in planta.
The aim of this thesis is to understand how the wheat, barley and oat grains protect themselves against Fusarium pathogens. The role of several HPC in resistance was investigated. A first preliminary study allowed us to understand the variability of the aggressiveness of Fusarium strains. We demonstrated that strain aggressiveness is related to the chemotype. Aggressiveness is mainly conditioned by the environment and not impacted by the resistance of the host. These observations have been necessary for both optimizing artificial inoculations in our field tests and interpreting the results of subsequent experiments. In a second study, we confirmed that CBS can contribute to FHB resistance in vivo. Indeed, we observed that, within a large panel of wheat genotypes, the most resistant varieties contained the highest contents of ferulic acid in the flower tissues. Following these results, the impact of FHB, the resistance elements and the contribution of different HPC in resistance have been successively studied in grains of wheat, barley and oat. For these studies, panels of wheat, barley and oat varieties have been artificially infected with Fusarium pathogens in different field tests across Switzerland. We observed that wheat grain displays the most complete resistance to protect itself against FHB damages DON accumulation and grain deformation. We have detected a novel resistance type that preserves the constituents and the baking quality of the grain. In barley grains, besides significant DON contamination, infections of F.graminearum caused damages on grain structure and composition. In particular, infection reduced the concentration of β-glucan in the grain. We demonstrated that the barley grain has distinct resistance elements to protect itself against fungal infection and toxin accumulation. In oat, we observed that both F.poae and F.langsethiae infections result in severe toxin contaminations, without any other symptoms or visual damages on the plant or the grain. Among the tested varieties, none was able to avoid contaminations. Our results suggest the presence of distinct resistance elements operating against the different Fusarium toxins.
The role of HPC in resistance depends on the compound. Our results show, that β-glucans reduce the mycotoxin charge in barley grains, while anthocyanins do not influence the resistance of wheat grains. In oat grain, accumulation of toxin was not modulated by β-glucans, yet increases of β-glucan contents were observed in grains resistant to nivalenol contamination.
To conclude, wheat, barley and oat protect themselves against Fusarium pathogens deploying different resistance mechanism. The stability and elevated heritability of resistance highlights the highest genetic gain that can be expected when selecting wheat for FHB resistance than in barley or oat. We demonstrated that if some HPC partially enhance grain resistance, enhancing HPC contents in grains will not drastically limit the threat associated with mycotoxins. However, it allows to develop new varieties that combine elevated HPC content and resistance to toxins.

2011, Tsai, Chia-Hong, Singh, Prashant, Chen, Ching-Wei, Thomas, Jerome, Weber, Johann, Mauch-Mani, Brigitte, Zimmerli, Laurent

The priming agent β-aminobutyric acid (BABA) is known to enhance Arabidopsis resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 by potentiating salicylic acid (SA) defence signalling, notably PR1 expression. The molecular mechanisms underlying this phenomenon remain unknown. A genome-wide microarray analysis of BABA priming during Pst DC3000 infection revealed direct and primed up-regulation of genes that are responsive to SA, the SA analogue benzothiadiazole and pathogens. In addition, BABA was found to inhibit the Arabidopsis response to the bacterial effector coronatine (COR). COR is known to promote bacterial virulence by inducing the jasmonic acid (JA) response to antagonize SA signalling activation. BABA specifically repressed the JA response induced by COR without affecting other plant JA responses. This repression was largely SA-independent, suggesting that it is not caused by negative cross-talk between SA and JA signalling cascades. Treatment with relatively high concentrations of purified COR counteracted BABA inhibition. Under these conditions, BABA failed to protect Arabidopsis against Pst DC3000. BABA did not induce priming and resistance in plants inoculated with a COR-deficient strain of Pst DC3000 or in the COR-insensitive mutant coi1-16. In addition, BABA blocked the COR-dependent re-opening of stomata during Pst DC3000 infection. Our data suggest that BABA primes for enhanced resistance to Pst DC3000 by interfering with the bacterial suppression of Arabidopsis SA-dependent defences. This study also suggests the existence of a signalling node that distinguishes COR from other JA responses.

2011, Lebeda, Ales, Holmes, Gerald J., Mauch-Mani, Brigitte, Jeger, Michael J.

2014, Ben Rejeb, I., Pastor, Victoria, Mauch-Mani, Brigitte

2011, Erb, Matthias, Balmer, Yves, de Lange, Elvira S., von Merey, Georg, Planchamp, Chantal, Robert, Christelle Aurélie Maud, Röder, Gregory, Sobhy, Islam, Zwahlen, Claudia, Mauch-Mani, Brigitte, Turlings, Ted

Determining links between plant defence strategies is important to understand plant evolution and to optimize crop breeding strategies. Although several examples of synergies and trade-offs between defence traits are known for plants that are under attack by multiple organisms, few studies have attempted to measure correlations of defensive strategies using specific single attackers. Such links are hard to detect in natural populations because they are inherently confounded by the evolutionary history of different ecotypes. We therefore used a range of 20 maize inbred lines with considerable differences in resistance traits to determine if correlations exist between leaf and root resistance against pathogens and insects. Aboveground resistance against insects was positively correlated with the plant's capacity to produce volatiles in response to insect attack. Resistance to herbivores and resistance to a pathogen, on the other hand, were negatively correlated. Our results also give first insights into the intraspecific variability of root volatiles release in maize and its positive correlation with leaf volatile production. We show that the breeding history of the different genotypes (dent versus flint) has influenced several defensive parameters. Taken together, our study demonstrates the importance of genetically determined synergies and trade-offs for plant resistance against insects and pathogens.

2011, Legay, Guillaume, Marouf, Elaheh, Berger, Dave, Neuhaus, Jean-Marc, Mauch-Mani, Brigitte, Slaughter, Ana R.

Grapevine (Vitis vinifera) is the most widely cultivated and economically important fruit crop, but is susceptible to a large number of diseases. Downy mildew, caused by the obligate biotrophic oomycete pathogen Plasmopara viticola, is a common disease present in all regions where vines are cultivated. We used suppression subtractive hybridization (SSH) to generate two cDNA libraries enriched for transcripts induced and repressed, respectively, in the susceptible grapevine cultivar Chasselas 24 h after inoculation with P. viticola. Differential screening on glass slide microarrays yielded over 800 putative genes that were up-regulated in response to P. viticola infection and over 200 that were down-regulated. One hundred and ninety four of these, were sequenced, identified and functionally categorised. Transcript abundance of twelve genes over a 48 h time course was examined by reverse transcriptase quantitative real-time PCR (RT-qPCR). Ten of these genes were induced/enhanced by P. viticola challenge, confirming the results of the SSH. The vast majority of the genes identified are related to defence. Interestingly, many genes involved in photosynthesis were down-regulated.