Preformed expression of defense is a hallmark of partial resistance to rice blast fungal pathogen Magnaporthe oryzae

Background: Partial resistance to plant pathogens is extensively used in breeding programs since it could contribute to resistance durability. Partial resistance often builds up during plant development and confers quantitative and usually broad-spectrum resistance. However, very little is known on the mechanisms underlying partial resistance. Partial resistance is often explained by poorly effective induction of plant defense systems. By exploring rice natural diversity, we asked whether expression of defense systems before infection could explain partial resistance towards the major fungal pathogen Magnaporthe oryzae. The constitutive expression of 21 defense-related genes belonging to the defense system was monitored in 23 randomly sampled rice cultivars for which partial resistance was measured. Results: We identified a strong correlation between the expression of defense-related genes before infection and partial resistance. Only a weak correlation was found between the induction of defense genes and partial resistance. Increasing constitutive expression of defense-related genes also correlated with the establishment of partial resistance during plant development. Some rice genetic sub-groups displayed a particular pattern of constitutive expression, suggesting a strong natural polymorphism for constitutive expression of defense. Constitutive levels of hormones like salicylic acid and ethylene cannot explain constitutive expression of defense. We could identify an area of the genome that contributes to explain both preformed defense and partial resistance. Conclusion: These results indicate that constitutive expression of defense-related genes is likely responsible for a large part of partial resistance in rice. The finding of this preformed defense system should help guide future breeding programs and open the possibility to identify the molecular mechanisms behind partial resistance. ( Résumé d'auteur

Phenotypic and transcriptomic analyses reveal major differences between apple and pear scab nonhost resistance

Nonhost resistance is the outcome of most plant/pathogen interactions, but it has rarely been described in Rosaceous fruit species. Apple (Malus x domestica Borkh.) have a nonhost resistance to Venturia pyrina, the scab species attacking European pear (Pyrus communis L.). Reciprocally, P. communis have a nonhost resistance to Venturia inaequalis, the scab species attacking apple. The major objective of our study was to compare the scab nonhost resistance in apple and in European pear, at the phenotypic and transcriptomic levels.  Macro- and microscopic observations after reciprocal scab inoculations indicated that, after a similar germination step, nonhost apple/V. pyrina interaction remained nearly symptomless, whereas more hypersensitive reactions were observed during nonhost pear/V. inaequalis interaction. Comparative transcriptomic analyses of apple and pear nonhost interactions with V. pyrina and V. inaequalis, respectively, revealed differences. Very few differentially expressed genes were detected during apple/V. pyrina interaction, preventing the inferring of underlying molecular mechanisms. On the contrary, numerous genes were differentially expressed during pear/V. inaequalis interaction, allowing a deep deciphering. Pre-invasive defense, such as stomatal closure, could be inferred, as well as several post-invasive defense mechanisms (apoplastic reactive oxygen species accumulation, phytoalexin production and alterations of the epidermis composition). In addition, a comparative analysis between pear scab host and nonhost interactions indicated that, although specificities were observed, two major defense lines seems to be shared in these resistances: cell wall and cuticle potential modifications and phenylpropanoid pathway induction. This first deciphering of the molecular mechanisms underlying a nonhost scab resistance in pear offers new possibilities for the genetic engineering of sustainable scab resistance in this species. Concerning nonhost scab resistance in apple, further analyses must be considered with the aid of tools adapted to this resistance with very few cells engaged

Putative role of arthropod vectors in African swine fever virus transmission in relation to their bio-ecological properties

African swine fever (ASF) is one of the most important diseases in Suidae due to its significant health and socioeconomic consequences and represents a major threat to the European pig industry, especially in the absence of any available treatment or vaccine. In fact, with its high mortality rate and the subsequent trade restrictions imposed on affected countries, ASF can dramatically disrupt the pig industry in afflicted countries. In September 2018, ASF was unexpectedly identified in wild boars from southern Belgium in the province of Luxembourg, not far from the Franco-Belgian border. The French authorities rapidly commissioned an expert opinion on the risk of ASF introduction and dissemination into metropolitan France. In Europe, the main transmission routes of the virus comprise direct contact between infected and susceptible animals and indirect transmission through contaminated material or feed. However, the seasonality of the disease in some pig farms in Baltic countries, including outbreaks in farms with high biosecurity levels, have led to questions on the possible involvement of arthropods in the transmission of the virus. This review explores the current body of knowledge on the most common arthropod families present in metropolitan France. We examine their potential role in spreading ASF—by active biological or mechanical transmission or by passive transport or ingestion—in relation to their bio-ecological properties. It also highlights the existence of significant gaps in our knowledge on vector ecology in domestic and wild boar environments and in vector competence for ASFV transmission. Filling these gaps is essential to further understanding ASF transmission in order to thus implement appropriate management measures

Basal expression of rice defence genes associated with partial resistance against Magnaporthe grisea

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Analyse des systèmes inductibles et préformés de défense du riz à Magnaporthe oryzae au travers de l'expression de gènes

Equipe 4Le riz constitue actuellement l’aliment de base de plus de la moitié de la population mondiale et l’une des maladies les plus importantes du riz est la pyriculariose, causée par le champignon phytopathogène Magnaporthe oryzae. Améliorer la résistance variétale du riz à Magnaporthe oryzae est donc un enjeu alimentaire et économique d’une portée considérable. Afin d’obtenir des variétés présentant une résistance durable, il est toutefois nécessaire d’améliorer notre connaissance des mécanismes de défense mis en place chez le riz pour contrer Magnaporthe oryzae. Au cours de ce travail de thèse nous nous sommes engagés dans une analyse transcriptomique intégrée des différentes formes de résistance présentes chez le riz, ainsi que dans l’étude approfondie d’un phénomène nouveau de la résistance préformée : l’expression constitutive des gènes de défense. Outre la mise en évidence et la validation de nouveaux marqueurs de l’expression inductible comme constitutive, il ressort de ce travail que la gestion de l’arsenal de défense est polymorphe. Ce travail montre également qu’il est possible d’identifier au sein du génome du riz des QTL de résistance à Magnaporthe oryzae probablement conditionnés par des gènes de défense ainsi que des QTL d’expression contrôlant simultanément l’expression constitutive de plusieurs gènes et contenant ainsi potentiellement des régulateurs centraux de ce phénomène nouveau de la résistance préformée du riz à Magnaporthe oryzae

Analyse des systèmes inductibles et préformés de défense du riz à Magnaporthe oryzae au travers de l'expression de gènes

Le riz constitue actuellement l'aliment de base de plus de la moitié de la population mondiale et l'une des maladies les plus importantes du riz est la pyriculariose, causée par le champignon phytopathogène Magnaporthe oryzae. Améliorer la résistance variétale du riz à Magnaporthe oryzae est donc un enjeu alimentaire et économique d'une portée considérable. Afin d'obtenir des variétés présentant une résistance durable, il est toutefois nécessaire d'améliorer notre connaissance des mécanismes de défense mis en place chez le riz pour contrer Magnaporthe oryzae. Au cours de ce travail de thèse nous nous sommes engagés dans une analyse transcriptomique intégrée des différentes formes de résistance présentes chez le riz, ainsi que dans l'étude approfondie d'un phénomène nouveau de la résistance préformée : l'expression constitutive des gènes de défense. Outre la mise en évidence et la validation de nouveaux marqueurs de l'expression inductible comme constitutive, il ressort de ce travail que la gestion de l'arsenal de défense est polymorphe. Ce travail montre également qu'il est possible d'identifier au sein du génome du riz des QTL de résistance à Magnaporthe oryzae probablement conditionnés par des gènes de défense ainsi que des QTL d'expression contrôlant simultanément l'expression constitutive de plusieurs gènes et contenant ainsi potentiellement des régulateurs centraux de ce phénomène nouveau de la résistance préformée du riz à Magnaporthe oryzaeRice is the staple food of more than the half of the world population and the rice blast disease, caused by the fungus Magnaporthe oryzae, is one of the most serious diseases of this crop. Breeding for resistance to the blast fungus is a considerable alimentary and economic issue. In order to get long-lasting resistance varieties, we need to improve our knowledge of defence reactions developed during rice blast disease resistance. In this study, we made an integrated analysis of the different forms of resistance present in rice, along with a detailed study of a novel preformed resistance phenomenon: the constitutive expression of defence genes. Besides the identification of new inducible and constitutive expression markers, we showed that the defence arsenal regulation is polymorphic. This work also points out that some disease resistance QTLs of rice are probably conditioned by defence genes. Besides, expression QTLs that simultaneously control the constitutive expression of several genes were identified. These regions potentially contain major regulators of this novel phenomenon of preformed resistanceMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Transfert intergénérique et fonctionnalité d’un gène majeur de résistance à la tavelure.

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An apple amiRNA efficiently silences the phytoene desaturase gene in apple.

National audienceArtificial miRNA (amiRNA) is a powerful technology to silence genes of interest with a high specificity, either to validate their function or to create new traits. To set up such a gene regulation tool for apple, we designed two amiRNA constructs based on an apple endogenous miRNA backbone that was previously characterized (Md-miRNA156h), and we checked their efficiency on an easily scorable marker gene: the phytoene desaturase gene (PDS). Two pairs of miRNA:miRNA* regions were designed according to the recommendations published by Whartman et al. (2008). The monocistronic Md-miRNA156h with these PDS targets was placed under the CaMV 35S promoter and cloned using the Gateway recombination method in the destination plasmid pK7WG2D, generating the two plasmids pAmiPDS-h and pAmiPDS-w. Two Agrobacterium-mediated transformation experiments were performed on the cultivar ‘Gala’, with a rate of transformation of 2 % for pAmiPDS-w and 3.4 % for pAmiPDS-h. In total, 5 and 10 independent transgenic clones were recovered, respectively. Most transgenic lines had a typical albino and dwarf phenotype. However, three clones had a wild type green phenotype. Molecular analyses are underway to correlate the phenotype with the degree of expression of the amiRNA gene and of the PDS gene. This study is the first demonstration in apple of the functionality of an amiRNA based on an endogenous miRNA backbone. It provides important opportunities for apple genetic functional studies as well as apple genetic improvement projects