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Rice yellow mottle virus (RYMV) causes one of the most devastating rice diseases in Africa. Management of RYMV is challenging. Genetic resistance provides the most effective and environment- friendly control. The recessive resistance locus rymv2 (OsCPR5.1) had been identified in African rice (O. glaberrima), however, introgression into O. sativa ssp. japonica and indica remains challenging due to crossing barriers. Here, we evaluated whether CRISPR/Cas9 genome editing of the two rice nucleoporin paralogs OsCPR5.1 (RYMV2) and OsCPR5.2 can be used to introduce RYMV resistance into the japonica variety Kitaake. Both paralogs had been shown to complement the defects of the Arabidopsis atcpr5 mutant, indicating partial redundancy. Despite striking sequence and structural similarities between the two paralogs, only oscpr5.1 loss-of-function mutants were fully resistant, while loss-of-function oscpr5.2 mutants remained susceptible, intimating that OsCPR5.1 plays a specific role in RYMV susceptibility. Notably, edited lines with short in-frame deletions or replacements in the N-terminal domain (predicted to be unstructured) of OsCPR5.1 were hypersusceptible to RYMV. In contrast to mutations in the single Arabidopsis AtCPR5 gene, which caused severely dwarfed plants, oscpr5.1 and oscpr5.2 single knockout mutants show neither substantial growth defects nor symptoms indicative of programmed cell death, possibly reflecting functional redundancy of the isoforms regarding other important functions. The specific editing of OsCPR5.1, while maintaining OsCPR5.2 activity, provides a promising strategy for generating RYMV-resistance in elite Oryza sativa lines as well as for effective stacking with other RYMV resistance genes or other traits.

International audience; Rice bacterial leaf blight (BLB) is caused by Xanthomonas oryzae pv. oryzae (Xoo) which injects Transcription Activator-Like Effectors (TALEs) into the host cell to modulate the expression of target disease susceptibility genes. Xoo major-virulence TALEs universally target susceptibility genes of the SWEET sugar transporter family. TALE-unresponsive alleles of OsSWEET genes have been identified in the rice germplasm or created by genome editing and confer resistance to BLB. In recent years, BLB has become one of the major biotic constraints to rice cultivation in Mali. To inform the deployment of alternative sources of resistance in this country, rice lines carrying alleles of OsSWEET14 unresponsive to either TalF (formerly Tal5) or TalC, two important TALEs previously identified in West African Xoo, were challenged with a panel of strains recently isolated in Mali and were found to remain susceptible to these isolates. The characterization of TALE repertoires revealed that talF and talC specific molecular markers were simultaneously present in all surveyed Malian strains, suggesting that the corresponding TALEs are broadly deployed by Malian Xoo to redundantly target the OsSWEET14 gene promoter. Consistent with this, the capacity of most Malian Xoo to induce OsSWEET14 was unaffected by either talC- or talF-unresponsive alleles of this gene. Long-read sequencing and assembly of eight Malian Xoo genomes confirmed the widespread occurrence of active TalF and TalC variants and provided a detailed insight into the diversity of TALE repertoires. All sequenced strains shared nine evolutionary related tal effector genes. Notably, a new TalF variant that is unable to induce OsSWEET14 was identified. Furthermore, two distinct TalB variants were shown to have lost the ability to simultaneously induce two susceptibility genes as previously reported for the founding members of this group from strains MAI1 and BAI3. Yet, both new TalB variants retained the ability to induce one or the other of the two susceptibility genes. These results reveal molecular and functional differences in tal repertoires and will be important for the sustainable deployment of broad-spectrum and durable resistance to BLB in West Africa.

Les plantes susceptibles d’établir une symbiose fixatrice d’azote avec l’actinomycète du sol Frankia sont appelées plantes actinorhiziennes. Ce sont principalement des plantes ligneuses, capables de coloniser des sols pauvres et de tolérer une grande variété de stress. Dans les régions tropicales arides et semi-arides, les arbres actinorhiziens de la famille des Casuarinaceae sont très utilisés pour réhabiliter les sols dégradés, protéger les zones côtières et les cultures de l’ensablement, et fournir du bois de chauffe. Les facultés d’adaptation de Casuarina aux sols carencés en éléments nutritifs sont liées à la plasticité racinaire remarquable de cet arbre qui adapte son programme de développement en fonction de son environnement. Les recherches entreprises dans notre laboratoire visent à comprendre les bases moléculaires de cette plasticité chez l’espèce Casuarina glauca. Des approches génomiques et des études d’analyse fonctionnelle de gènes candidats sont développées en partenariat avec des laboratoires du Sud.

L’initiative de la Grande Muraille Verte (GMV), projet transcontinental, est une réponse de l’Afrique à la désertification, à la pauvreté et au changement climatique. Elle repose sur une approche concertée, multisectorielle, mettant en synergie des actions de lutte contre ces trois fléaux majeurs pour le continent africain. La particularité de la GMV est, tout en créant et consolidant une ligne de défense par des activités de reboisement et d’aménagement, de contribuer efficacement au développement intégré des zones rurales et d’aider à la lutte contre la pauvreté dans le cadre d’un développement durable. Il s’agit de l’installation et de la mise en valeur intégrée d’espèces végétales à valeur économique adaptées aux terres arides et aux particularités locales, de bassins de rétention, de systèmes de production agricoles et autres activités génératrices de revenus. La GMV intègre ainsi plusieurs systèmes des plantations artificielles anciennes ou nouvelles, des unités agro-sylvo-pastorales. Des zones de parcours villageoises ou intercommunautaires, des parcs animaliers, des réserves communautaires et des couloirs de migration de faune. Cet édifice transcontinental est une référence de modèle d’intégration sous-régional mettant en exergue une initiative originale initiée par des pays fortement assujettis aux phénomènes de désertification et de changement climatique Il constitue un Modèle Multisectoriel de Développement Intégré des Zones Andes (MDI/ZA). Dédié à la lutte contre tes effets et l’avancée de la désertification, à la restauration et la mise en valeur des zones dégradées et au mécanisme de développement propre dû à sa forte capacité de séquestration de carbone. L’ouvrage vise un large public, notamment les scientifiques, enseignants, décideurs, techniciens charges de la mise en œuvre de la GMV et permet d’apprécier l’originalité du projet dans son approche concertée et multisectorielle et ses résultats dans le développement intégré des zones arides a semi-arides.

Soil and tailings contamination in the eastern region of Morocco was investigated by determining metallic trace elements (MTE) (As, Cd, Cu, Ni, Pb and Zn) using inductively coupled plasma-atomic emission spectrometry (ICP-AES). This work revealed extensive contamination of the sites studied and also showed a great variability in the concentrations of MTE according to the element analyzed and the site. The soil index pollution is considered very high because of the simultaneous presence of these elements. This combination of MTE in soils makes the region toxic to flora, fauna and local populations. An exploration of plant species growing on these contaminated areas will be considered in the context of the implementation of a program for phytoremediation., La contamination des sols et des résidus miniers dans la région orientale du Maroc a été évaluée par dosage des éléments-traces métalliques (ETM) (As, Cd, Cu, Ni, Pb et Zn) par ICP-AES (inductively coupled plasma-atomic emission spectrometry). Ce travail révèle une contamination importante des sites étudiés et souligne une grande variabilité dans les concentrations en ETM en fonction de l’élément analysé et du site étudié. L’index de pollution des stations étudiées est généralement très élevé du fait de la présence simultanée de plusieurs de ces éléments. Cette combinaison de différents ETM rend les sols de la région toxiques pour la flore, la faune et les populations locales. Une analyse des espèces végétales qui se développent sur ces zones polluées est envisagée dans le cadre de la mise en place d’un programme de phyto-remédiation.

La contamination des sols et des résidus miniers dans la région orientale du Maroc a été évaluée par dosage des éléments-traces métalliques (ETM) (As, Cd, Cu, Ni, Pb et Zn) par ICP-AES (inductively coupled plasma-atomic emission spectrometry). Ce travail révèle une contamination importante des sites étudiés et souligne une grande variabilité dans les concentrations en ETM en fonction de l_élément analysé et du site étudié. L'index de pollution des stations étudiées est généralement trés élevé du fait de la présence simultaneée de plusieurs de ces éléments. Cette combinaison de différents ETM rend les sols de la région toxiques pour la flore, la faune et les populations locales. Une analyse des espèces végétales qui se développent sur ces zones polluées est envisagée dans le cadre de la mise en place d'un programme de phytoremédiation

After water and light, nitrogen and phosphorus are the major elements limiting plant production worldwide. The use of fertilizers to offset these deficiencies is now actively disapproved because of their high price, their effect on climate change and their negative environmental impact. One solution could be to exploit plants that have acquired the ability to adapt to deficient environments. One example is given by plants that develop symbiotic associations with nitrogen-fixing bacteria in order to benefit from the large reservoir of atmospheric nitrogen. Two groups of plants are known to form nitrogen-fixing root nodules: legumes that associate with rhizobia and plants belonging to eight angiosperm families, called actinorhizal plants, that associate with the actinomycete Frankia. These plants can thrive on nitrogen-poor soil and have long been used to increase soil fertility. Among them, Casuarina a tropical tree originating from Australia, presents a very important ecological asset for Southern countries due to its high ability to colonize deficient soils. Our team has focused on the cellular and molecular studies of the plant genes involved at different steps of the interaction between Frankia and Casuarina glauca. Several candidate genes from Casuarina have been characterized, including cg12, a subtilase gene expressed during early infection events, CgMT1 a metallothionein gene involved in stress responses and CgSymRK, a gene from the signalling pathway involved at the beginning of the symbiosis. More recently, a genomic approach has been initiated in order to sequence the ESTs from roots and nodules of Casuarina. Comparison between our data and legumes EST databases should reveal molecular mechanisms that are common and unique to the two endophytic root nodule symbioses and bring new information to further our understanding of the evolution of plant endosymbiosis across the plant kingdom.

The symbiosis between the actinorhizal tree Allocasuarina verticillata and the actinomycete Frankia leads to the formation of root nodules inside which bacteria fix atmospheric nitrogen. Actinorhizal nodule organogenesis starts with the induction of cell divisions in the root cortex and in the pericycle cells opposite protoxylem poles near Frankia-infected root hairs. To study the ability of Frankia to induce progression through the cell cycle, we monitored the expression of the beta-glucuronidase (gus) gene driven by the promoter from cdc2aAt, an Arabidopsis cyclin-dependent kinase gene that displays competence for cell division, during plant growth and nodule ontogenesis. In non-symbiotic tissues, the gus gene was mainly expressed in primary and secondary meristems of roots and shoots. Auxins and cytokinins were found to induce reporter gene activity in the root system of whole plants, showing that the promoter cdc2aAt displayed the same regulation by hormones in Allocasuarina as that reported in Arabidopsis. In transgenic nodules, gus expression was found to be restricted to the phellogen. During the early stages of the interaction between Frankia and the plant root system, cdc2aAt was strongly induced in the lateral roots surrounded by hyphae of the actinomycete. Histochemical analysis of beta-glucuronidase activity revealed that cells from the pericycle opposite protoxylem poles were very deeply stained. These data indicate that upon Frankia infection, cells from the lateral roots, and notably pericycle cells that can give rise to a nodule or a root primordium, prepare to re-enter the cell cycle.

cgMT1 is a metallothionein (MT)-like gene that was isolated from a cDNA library of young nitrogen-fixing nodules resulting from the symbiotic interaction between Frankia spp. and the actinorhizal tree Casuarina glauca. cgMT1 is highly transcribed in the lateral roots and nitrogen-fixing cells of actinorhizal nodules; it encodes a class I type 1 MT. To obtain insight into the function of cgMT1, we studied factors regulating the expression of the MT promoter region (PcgMT1) using a beta-glucuronidase (gus) fusion approach in transgenic plants of Arabidopsis thaliana. We found that copper, zinc, and cadmium ions had no significant effect on the regulation of PcgMT1-gus expression whereas wounding and H2O2 treatments led to an increase in reporter gene activity in transgenic leaves. Strong PcgMT1-gus expression also was observed when transgenic plants were inoculated with a virulent strain of the bacterial pathogen Xanthomonas campestris pv. campestris. Transgenic Arabidopsis plants expressing cgMT1 under the control of the constitutive 35S promoter were characterized by reduced accumulation of H2O2 when leaves were wounded and by increased susceptibility to the bacterial pathogen X. campestris. These results suggest that cgMT1 could play a role during the oxidative response linked to biotic and abiotic stresses.