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Opines are produced in plant cells transformed with the A. tumefaciens T-DNA. These opines can be used as nutrients by the phytopathogen and some of them act as signaling molecules controlling Ti plasmid dissemination through quorum-sensing. The present study aims at an enlarged understanding of the roles of opines during A. tumefaciens/plant host interactions. First, based on transcriptomic investigations, the agrocinopine-controled AccR regulon from A. tumefaciens C58 was thoroughly characterized. This one includes functions associated with (i) agrocinopines assimilation, (ii) nopaline assimilation, (iii) quorum-sensing and Ti plasmid conjugation, (iv) At plasmid conjugation. Moreover our analysis showed that co-regulation of Ti and At plasmid conjugations correlated with the co-transfer of the two replicons. In a second step using functional genetic and structural biology we quantified the selective advantage conferred to colonizing A. tumefaciens populations by the assimilation of the opines nopaline and octopine. The molecular basis which underlies this selective advantage, especially regarding the sensing and import of the two opines within the bacterial cytoplasm, were also described. Finally combining metabolomics and reverse genetic with in planta conjugation assays we demonstrated the opposite effects of GABA and opine/quorum-sensing signaling on the dissemination of Ti plasmids. In conclusion our results reveal the interlink between opine, quorum-sensing and GABA signaling during A. tumefaciens/plant host interactions. They noticeably highlight the impact of this interlink on host colonization and the dissemination of Ti and At plasmid genes which are critical for the virulence and the adaption of the bacteria to the tumor lifestyle., Les opines sont des molécules produites dans les cellules végétales transformées par l’ADN-T d’A. tumefaciens. Ces opines peuvent être utilisées comme nutriments par le phytopathogène et certaines d’entre elles agissent comme signaux moléculaires contrôlant la dissémination du plasmide de virulence Ti via la signalisation quorum-sensing. Le présent travail vise à une compréhension élargie du rôle des opines au cours des interactions A. tumefaciens-plantes hôtes. En se basant d’abord sur des analyses transcriptomiques, le régulon AccR d’A. tumefaciens C58, contrôlé par les opines agrocinopines, a été défini : celui-ci inclut des fonctions associées (i) à l’assimilation des agrocinopines, (ii) à l’assimilation de la nopaline, (iii) à la signalisation quorum-sensing et la conjugaison du plasmide Ti, (iv) à la conjugaison du plasmide At. La corrélation entre la co-régulation des conjugaisons des plasmides Ti et At et le co-transfert des deux réplicons a en outre été mise en évidence. Dans un second temps, associant des approches de génétique fonctionnelle à des travaux collaboratifs en biologie structurale, l’avantage sélectif conféré par les opines nopaline et octopine à A. tumefaciens au sein des tumeurs végétales a été quantifié. Les bases moléculaires sous-jacentes à cet avantage sélectif, notamment celles associées à la perception et l’importation des deux opines dans le cytoplasme bactérien, ont été décrites. Enfin, en combinant des approches de métabolomique et de génétique inverse avec des tests de conjugaison in planta, les effets opposés de la signalisation GABA d’une part et des signalisations opine et quorum-sensing d’autre part sur la dissémination du plasmide Ti ont été démontrés. En conclusion, nos résultats révèlent l’intrication des signalisations opine, quorum-sensing et GABA au cours de l’interaction A. tumefaciens-plantes hôtes. Ils soulignent en particulier les impacts de cette intrication sur la colonisation de l’hôte ainsi que sur la dissémination des gènes de virulence et d’adaptation à l’environnement tumeur portés par les plasmides Ti et At.

International audience; The plant pathogen Agrobacterium tumefaciensC58 harbours three independent type IV secretion (T4SS) machineries. T4SS(T-DNA) promotes the transfer of the T-DNA to host plant cells, provoking tumour development and accumulation of opines such as nopaline and agrocinopines. T4SS(pTi) and T4SS(pAt) control the bacterial conjugation of the Ti and At plasmids respectively. Expression of T4SS(pTi) is controlled by the agrocinopine-responsive transcriptional repressor AccR. In this work, we compared the genome-wide transcriptional profile of the wild-type A.tumefaciens strain C58 with that of its accR KO-mutant to delineate the AccR regulon. In addition to the genes that encode agrocinopine catabolism and T4SS(pTi), we found that AccR also regulated genes coding for nopaline catabolism and T4SS(pAt). Further opine detection and conjugation assays confirmed the enhancement of nopaline consumption and At plasmid conjugation frequency in accR. Moreover, co-regulation of the T4SS(pTi) and T4SS(pAt) correlated with the co-transfer of the At and Ti plasmids both in vitro and in plant tumours. Finally, unlike T4SS(pTi), T4SS(pAt) activation does not require quorum-sensing. Overall this study highlights the regulatory interplays between opines, At and Ti plasmids that contribute to a concerted dissemination of the two replicons in bacterial populations colonizing the plant tumour.

International audience; During the past ten years, emerging data revealed the role of E2F factors in various plant physiology aspects. E2F involvement in cell cycle and plant development was particularly investigated and highlighted some plant specificities, espacially in postembryonic development. A major role of E2F is its transcriptional activity governing specific gene induction throughout the cell cycle and also strong induction of DNA repair genes in response to DNA damage, notably in the context of DNA double strand break (DSB) response. More challenging is the implication of E2F in nuclear foci with gamma-H2AX, a marker of DSB, probably independently of its transcriptional activity, in the DNA damage response.