Etude du rôle des cytokinines végétales et fongiques dans l'interaction riz-Magnaporthe oryzae

The blast disease caused by Magnaporthe oryzae is one of the most devastating diseases on rice leading to important yield loss. Plant hormones, like salicylic acid, play a central role in plant resistance establishment. Among these hormones, cytokinins (CKs) are adenine derivatives well described to modulate root/shoot growth and differentiation, cell viability and nutrient distribution. Previous studies have shown that these hormonal compounds can also affect plant host resistance in different pathosystems involving monocot or dicot host plants and microbes (bacteria, oomycetes or fungi). In rice, CKs were described to act synergistically with the salicylic acid pathway to induce defense marker genes expression. However, no resistance phenotype associated with CKs was observed and the way that CKs could act in planta during infection is still unknown. In this work, a resistance phenotype induced by exogenous application of the CK kinetin was characterized and the role of endogenous CKs in rice resistance was investigated by phenotyping plant CK mutants. An exogenous supply of kinetin before infection led to a higher induction of defense marker genes that was associated with limited fungal penetration and invasion, suggesting. However the way CKs affected resistance or susceptibility (or virulence see below) depended on the timing at which they were applied (before or after inoculation). Rice lines mutated for a putative cytokinin- UDP-glycosyl transferase (CK-UGT) were produced. The ck-ugt mutants were more resistant, suggesting that endogenous CKs can also contribute to resistance. Defense marker genes were expressed higher in the absence of infection in the ck-ugt rice mutants, compared to the WT plants. In parallel of these analyses of CK on the plant side, we studied the possible role of CK produced by Magnaporthe. Indeed M.oryzae produces and secretes CKs. However, the way fungal CKs are involved in the rice blast disease development as well as the biosynthesis pathway in M.oryzae were not established. A putative tRNA-IPT (isopentenyl transferase) conserved across organisms was identified in M.oryzae. Mutant analysis of this gene confirmed that this enzyme, thus named CKS1, is required for CK production. Knock-out cks1 fungal mutants were less virulent on rice, affected in penetration and invasion compared to the control complemented strain. They triggered a stronger accumulation of reactive oxygen species and a higher expression of defense marker genes. Aspartate and glutamate, two amino acids important for M.oryzae growth, were differently affected at and around the infected zone by cks1 strain suggesting that fungal CKs could contribute to drain/consume nutrients during infection. Similarly, sugar accumulation was also differently disturbed, indicating that fungal-derived CKs may be required for maintaining a progressive sugar production during host invasion, probably by affecting photosynthesis process. Our results show that fungal CKs, in a non-gall forming fungal pathogen, could act as dual effectors by inhibiting defense and modifying nutrient fluxes. Furthermore, CKs are known to affect some physiological processes in fungi, like stress resistance, nutrition or sexual reproduction. In order to test whether CKs modulate Magnaporthe stress tolerance, the effect of CKs on the mycelial growth in different stressful conditions in vitro was tested. The results indicate that CKs increased osmotic and oxidative stress tolerance and suggest that they also affected nutrient acquisition as well as sexual reproduction. Since the CKS1 gene is highly conserved, the effect of the cks1 mutation could be studied in other fungi showing different lifestyles for improving our knowledge on the role these hormonal compounds play among microbes or in plant-microbe interactions.Magnaporthe oryzae est un champignon filamenteux responsable de la principale maladie du riz, la pyriculariose. Ce pathosystème est très étudié, notamment dans le but de contribuer à l’identification de facteurs pouvant permettre le développement de résistances efficaces. Si certaines hormones végétales, comme l’acide salycilique, sont requises pour la mise en place des défenses de la plante, d’autres sont impliquées dans des processus développementaux. Parmi elles, les cytokinines (CKs) sont des dérivés d’adénine décrites pour participer à la croissance et la différenciation de l’appareil aérien et racinaire. Elles contribuent à la répartition des nutriments et impactent également la viabilité des cellules, en retardant la senescence ou en induisant la mort cellulaire. Des études précédentes ont montré que les CKs pouvaient perturber la résistance de la plante hôte dans différents pathosystèmes. Chez le riz, les CKs agissent en synergie avec l’acide salicylique pour induire l’expression des gènes marqueurs des défenses. Cependant aucun phénotype de résistance associé aux CKs n’a été observé in planta. Mes travaux montrent qu’un apport exogène de CKs (kinétine, BAP) affecte la résistance du riz à Magnaporthe avant infection, de manière dose dépendante. Le phénotype de résistance observé est corrélé avec une plus forte expression des défenses pendant infection, limitant la pénétration et l’invasion du champignon. Des plantes de riz mutées pour une probable cytokinine UDP-glucosyl transferase (CK-UGT) ont été obtenues. Ces mutants ck-ugt sont affectés dans le métabolisme des CKs et sont également plus résistants à M. oryzae. Hors infection, une plus forte expression des gènes de défense a été mesurée chez les plantes mutantes, confirmant que les CKs endogènes affectent directement ou indirectement les défenses de l’hôte. En parallèle de ces analyses sur la plante, mes travaux ont aussi porté sur le rôle des CKs produites par M.oryzae. En effet, leur rôle dans l’interaction ainsi que la voie de leur biosynthèse chez le champignon n’était pas caractérisé. Conservées au sein des différents organismes, les tRNA-IPT (isopentenyl transferase) sont décrites pour participer à la biosynthèse de CKs. Un seul gène homologue a été identifié chez M. oryzae et nommé CKS1 car sa délétion abolit la production de CKs. Le mutant de Magnaporthe cks1 est moins virulent (pénétration et invasion in planta réduites) que la souche témoin complémentée. Il induit une plus forte accumulation des espèces actives de l’oxygène et une plus forte expression des défenses chez la plante. Les dosages des acides aminés et des sucres pendant infection ont montré que les concentrations de ces nutriments étaient différemment perturbées par la souche déficiente en CKs. Ces résultats suggèrent que les CKs fongiques pourraient être requises pour affecter la répartition des acides aminés et contribuer une accumulation progressive de sucres au cours de l’infection. Ainsi, chez un champignon qui n’induit pas de tumeurs, les CKs pourraient agir comme des effecteurs qui auraient une double fonction d’inhibition des défenses et de drainage des nutriments. Chez les champignons, ces hormones induisent également des réponses physiologiques comme la résistance à certains stress, les processus de nutrition et la reproduction sexuée. Ces effets ont été étudiés chez Magnaporthe dans différentes conditions de croissance in vitro plus ou moins stressantes. Les résultats indiquent que les CKs augmentent la tolérance au stress osmotique et oxydatif et suggèrent qu’elles affecteraient aussi l’absorption des nutriments ainsi que la reproduction sexuée. Comme le gène CKS1 est conservé, cette mutation peut être caractérisée chez d’autres organismes fongiques présentant des modes de vie différents de manière à mieux comprendre le rôle de ces hormones dans les interactions plante-microorganisme mais également au sein des interactions microbiennes

Study of the role of plant and fungal cytokinins in the pathosystem rice-Magnaporthe oryzae

Magnaporthe oryzae est un champignon filamenteux responsable de la principale maladie du riz, la pyriculariose. Ce pathosystème est très étudié, notamment dans le but de contribuer à l’identification de facteurs pouvant permettre le développement de résistances efficaces. Si certaines hormones végétales, comme l’acide salycilique, sont requises pour la mise en place des défenses de la plante, d’autres sont impliquées dans des processus développementaux. Parmi elles, les cytokinines (CKs) sont des dérivés d’adénine décrites pour participer à la croissance et la différenciation de l’appareil aérien et racinaire. Elles contribuent à la répartition des nutriments et impactent également la viabilité des cellules, en retardant la senescence ou en induisant la mort cellulaire. Des études précédentes ont montré que les CKs pouvaient perturber la résistance de la plante hôte dans différents pathosystèmes. Chez le riz, les CKs agissent en synergie avec l’acide salicylique pour induire l’expression des gènes marqueurs des défenses. Cependant aucun phénotype de résistance associé aux CKs n’a été observé in planta. Mes travaux montrent qu’un apport exogène de CKs (kinétine, BAP) affecte la résistance du riz à Magnaporthe avant infection, de manière dose dépendante. Le phénotype de résistance observé est corrélé avec une plus forte expression des défenses pendant infection, limitant la pénétration et l’invasion du champignon. Des plantes de riz mutées pour une probable cytokinine UDP-glucosyl transferase (CK-UGT) ont été obtenues. Ces mutants ck-ugt sont affectés dans le métabolisme des CKs et sont également plus résistants à M. oryzae. Hors infection, une plus forte expression des gènes de défense a été mesurée chez les plantes mutantes, confirmant que les CKs endogènes affectent directement ou indirectement les défenses de l’hôte. En parallèle de ces analyses sur la plante, mes travaux ont aussi porté sur le rôle des CKs produites par M.oryzae. En effet, leur rôle dans l’interaction ainsi que la voie de leur biosynthèse chez le champignon n’était pas caractérisé. Conservées au sein des différents organismes, les tRNA-IPT (isopentenyl transferase) sont décrites pour participer à la biosynthèse de CKs. Un seul gène homologue a été identifié chez M. oryzae et nommé CKS1 car sa délétion abolit la production de CKs. Le mutant de Magnaporthe cks1 est moins virulent (pénétration et invasion in planta réduites) que la souche témoin complémentée. Il induit une plus forte accumulation des espèces actives de l’oxygène et une plus forte expression des défenses chez la plante. Les dosages des acides aminés et des sucres pendant infection ont montré que les concentrations de ces nutriments étaient différemment perturbées par la souche déficiente en CKs. Ces résultats suggèrent que les CKs fongiques pourraient être requises pour affecter la répartition des acides aminés et contribuer une accumulation progressive de sucres au cours de l’infection. Ainsi, chez un champignon qui n’induit pas de tumeurs, les CKs pourraient agir comme des effecteurs qui auraient une double fonction d’inhibition des défenses et de drainage des nutriments. Chez les champignons, ces hormones induisent également des réponses physiologiques comme la résistance à certains stress, les processus de nutrition et la reproduction sexuée. Ces effets ont été étudiés chez Magnaporthe dans différentes conditions de croissance in vitro plus ou moins stressantes. Les résultats indiquent que les CKs augmentent la tolérance au stress osmotique et oxydatif et suggèrent qu’elles affecteraient aussi l’absorption des nutriments ainsi que la reproduction sexuée. Comme le gène CKS1 est conservé, cette mutation peut être caractérisée chez d’autres organismes fongiques présentant des modes de vie différents de manière à mieux comprendre le rôle de ces hormones dans les interactions plante-microorganisme mais également au sein des interactions microbiennes.The blast disease caused by Magnaporthe oryzae is one of the most devastating diseases on rice leading to important yield loss. Plant hormones, like salicylic acid, play a central role in plant resistance establishment. Among these hormones, cytokinins (CKs) are adenine derivatives well described to modulate root/shoot growth and differentiation, cell viability and nutrient distribution. Previous studies have shown that these hormonal compounds can also affect plant host resistance in different pathosystems involving monocot or dicot host plants and microbes (bacteria, oomycetes or fungi). In rice, CKs were described to act synergistically with the salicylic acid pathway to induce defense marker genes expression. However, no resistance phenotype associated with CKs was observed and the way that CKs could act in planta during infection is still unknown. In this work, a resistance phenotype induced by exogenous application of the CK kinetin was characterized and the role of endogenous CKs in rice resistance was investigated by phenotyping plant CK mutants. An exogenous supply of kinetin before infection led to a higher induction of defense marker genes that was associated with limited fungal penetration and invasion, suggesting. However the way CKs affected resistance or susceptibility (or virulence see below) depended on the timing at which they were applied (before or after inoculation). Rice lines mutated for a putative cytokinin- UDP-glycosyl transferase (CK-UGT) were produced. The ck-ugt mutants were more resistant, suggesting that endogenous CKs can also contribute to resistance. Defense marker genes were expressed higher in the absence of infection in the ck-ugt rice mutants, compared to the WT plants. In parallel of these analyses of CK on the plant side, we studied the possible role of CK produced by Magnaporthe. Indeed M.oryzae produces and secretes CKs. However, the way fungal CKs are involved in the rice blast disease development as well as the biosynthesis pathway in M.oryzae were not established. A putative tRNA-IPT (isopentenyl transferase) conserved across organisms was identified in M.oryzae. Mutant analysis of this gene confirmed that this enzyme, thus named CKS1, is required for CK production. Knock-out cks1 fungal mutants were less virulent on rice, affected in penetration and invasion compared to the control complemented strain. They triggered a stronger accumulation of reactive oxygen species and a higher expression of defense marker genes. Aspartate and glutamate, two amino acids important for M.oryzae growth, were differently affected at and around the infected zone by cks1 strain suggesting that fungal CKs could contribute to drain/consume nutrients during infection. Similarly, sugar accumulation was also differently disturbed, indicating that fungal-derived CKs may be required for maintaining a progressive sugar production during host invasion, probably by affecting photosynthesis process. Our results show that fungal CKs, in a non-gall forming fungal pathogen, could act as dual effectors by inhibiting defense and modifying nutrient fluxes. Furthermore, CKs are known to affect some physiological processes in fungi, like stress resistance, nutrition or sexual reproduction. In order to test whether CKs modulate Magnaporthe stress tolerance, the effect of CKs on the mycelial growth in different stressful conditions in vitro was tested. The results indicate that CKs increased osmotic and oxidative stress tolerance and suggest that they also affected nutrient acquisition as well as sexual reproduction. Since the CKS1 gene is highly conserved, the effect of the cks1 mutation could be studied in other fungi showing different lifestyles for improving our knowledge on the role these hormonal compounds play among microbes or in plant-microbe interactions

Plant Hormones: Key Players in Gut Microbiota and Human Diseases?

It is well established that plant hormones such as auxins, cytokinins (CKs), and abscisic acid (ABA) not only govern important plant physiological traits but are key players in plant–microbe interactions. A poorly appreciated fact, however,is that both microbes and animals produce and perceive plant hormones and their mimics. Moreover, dietary plant hormones impact on human physiological process such as glucose assimilation, inflammation, and cell division. This leads us to wonder whether plant hormones could ensure functions in microbes per se as well as in animal–microbe interactions. We propose here and explore the hypothes is that plant hormones play roles in animal–microbiota relation-ships, with consequences for human healt

Plant hormones: a fungal point of view

International audienceMost classical plant hormones are also produced by pathogenic and symbiotic fungi. The way these molecules favor the invasion of plant tissues and the development of fungi inside plant tissues is still largely unknown. In this review, we examine the different roles of such hormone production by pathogenic fungi. Converging evidence suggest that these fungal-derived molecules have potentially two modes of action: (i) they may perturb plant processes, either positively or negatively, to favor invasion and nutrient uptake and (ii) they may also act as signals for the fungi themselves to engage appropriate developmental and physiological processes adapted to their environment. Indirect evidences suggest that abscisic acid, gibberellic acid and ethylene produced by fungi participate to pathogenicity. There is now evidence that auxin and cytokinins could be positive regulators required for virulence. Further research should establish whether or not fungal-derived hormones act like other fungal effectors

Hors de chez moi et accessible, c’est possible?

Invisible, l’hyperréactivité aux stimulations sonores rend complexe le choix d’une activité. Une étude pluridisciplinaire a abouti à la création d’un prototype de technologie numérique qui aide les individus à se projeter dans leurs loisirs

Transcriptome sequencing of infected wheat samples collected during the wheat blast epidemic in Bangladesh in 2017 and release of raw sequence data on OpenWheatBlast website with open access

Wheat fields in Bangladesh were again infected by wheat blast fungus (<i>Magnaporthe oryzae</i>) in 2017 growing season, following the epidemic of 2016. Infected wheat samples were collected by Tofazzal Islam and team, and sent to the Sainsbury Laboratory for RNA extraction and sequencing. Library preparation and RNA-Seq sequencing runs were performed on Illumina HiSeq-2500 machines at the Earlham Institute to produce paired-end reads with ~267 bp average insert size. Here we report the release of these data to general public with open access on OpenWheatBlast website.<br

Cytokinin production by the rice blast fungus is a pivotal requirement for full virulence

BGPI : équipe 4International audiencePlants produce cytokinin (CK) hormones for controlling key developmental processes like source/sink distribution, cell division or programmed cell-death. Some plant pathogens have been shown to produce CKs but the function of this mimicry production by non-tumor inducing pathogens, has yet to be established. Here we identify a gene required for CK biosynthesis, CKS1, in the rice blast fungus Magnaporthe oryzae. The fungal-secreted CKs are likely perceived by the plant during infection since the transcriptional regulation of rice CK-responsive genes is altered in plants infected by the mutants in which CKS1 gene was deleted. Although cks1 mutants showed normal in vitro growth and development, they were severely affected for in planta growth and virulence. Moreover, we showed that the cks1 mutant triggered enhanced induction of plant defenses as manifested by an elevated oxidative burst and expression of defense-related markers. In addition, the contents of sugars and key amino acids for fungal growth were altered in and around the infection site by the cks1 mutant in a different manner than by the control strain. These results suggest that fungal-derived CKs are key effectors required for dampening host defenses and affecting sugar and amino acid distribution in and around the infection site

Plant probiotic bacteria suppress wheat blast fungus Magnaporthe oryzae Triticum pathotype

<b>Biological control of fearsome wheat blast by bacterial antagonist from native environment.</b

Genome sequences of candidate wheat blast biocontrol bacteria

In an effort to combat wheat blast disease in Bangladesh, Prof. Tofazzal Islam and team have identified several biocontrol bacteria that have the ability to inhibit fungal growth in wheat (Surovy et al., 2017). They have isolated a number of these agents and we have sequenced the genomes of four bacterial strains to 30x coverage. The genome sequence data is now available to download from links in the tables included in the document.<br

The Rice DNA-Binding Protein ZBED Controls Stress Regulators and Maintains Disease Resistance After a Mild Drought

Background: Identifying new sources of disease resistance and the corresponding underlying resistance mechanisms remains very challenging, particularly in Monocots. Moreover, the modification of most disease resistance pathways made so far is detrimental to tolerance to abiotic stresses such as drought. This is largely due to negative cross-talks between disease resistance and abiotic stress tolerance signaling pathways. We have previously described the role of the rice ZBED protein containing three Zn-finger BED domains in disease resistance against the fungal pathogen Magnaporthe oryzae. The molecular and biological functions of such BED domains in plant proteins remain elusive.Results: Using Nicotiana benthamiana as a heterologous system, we show that ZBED localizes in the nucleus, binds DNA, and triggers basal immunity. These activities require conserved cysteine residues of the Zn-finger BED domains that are involved in DNA binding. Interestingly, ZBED overexpressor rice lines show increased drought tolerance. More importantly, the disease resistance response conferred by ZBED is not compromised by drought-induced stress.Conclusions: Together our data indicate that ZBED might represent a new type of transcriptional regulator playing simultaneously a positive role in both disease resistance and drought tolerance. We demonstrate that it is possible to provide disease resistance and drought resistance simultaneously