Actinorhizal nitrogen fixing nodules: infection process, molecular biology and genomics

Actinorhizal hosts are non-leguminous perennial plants belonging to 8 angiosperm families. They are capable of forming root nodules as a result of infection by a nitrogen-fixing actinomycete called Frankia. Actinorhizal nodules consist of multiple lobes, each of which represents a modified lateral root with infected cells in the expanded cortex. This article summarizes the most recent knowledge about this original symbiotic process. The infection process is described both at cytological and molecular levels. The use of transgenic Casuarinaceae for studying in actinorhizal nodules the regulation of several symbiotic promoters from legumes is also discussed. With progress in plant genome sequencing, comparative genomics in legumes and actinorhizal plants should contribute to the understanding of the evolutionary history of nitrogen-fixing symbioses. Key words : Nitrogen-fixation, actinorhizal nodules, Frankia, Casuarina, symbiotic gene. African Journal of Biotechnology Vol. 2 (12), pp. 528-538, December 200

Transcriptome changes in Hirschfeldia incana in response to lead exposure

Hirschfeldia incana, a pseudometallophyte belonging to the Brassicaceae family and widespread in the Mediterranean region, was selected for its ability to grow on soils contaminated by lead (Pb). The global comparison of gene expression using microarrays between a plant susceptible to Pb (Arabidopsis thaliana) and a Pb tolerant plant (H. incana) enabled the identification of a set of specific genes expressed in response to lead exposure. Three groups of genes were particularly over-represented by the Pb exposure in the biological processes categorized as photosynthesis, cell wall, and metal handling. Each of these gene groups was shown to be directly involved in tolerance or in protection mechanisms to the phytotoxicity associated with Pb. Among these genes, we demonstrated that MT2b, a metallothionein gene, was involved in lead accumulation, confirming the important role of metallothioneins in the accumulation and the distribution of Pb in leaves. On the other hand, several genes involved in biosynthesis of ABA were shown to be up regulated in the roots and shoots of H. incana treated with Pb, suggesting that ABA-mediated signaling is a possible mechanism in response to Pb treatment in H. incana. This latest finding is an important research direction for future studies

Identification of genes involved in lead tolerance in Hirschfeldia incana (brassicaceae)

L'exploitation, puis l'abandon, des sites miniers, dans l'oriental marocain, a entraîné une importante pollution des zones avoisinantes, générée par la dispersion de déchets riches en Pb. Pour résoudre ce problème, des programmes de phytomanagement sont à développer. Cependant, la réalisation de ces projets se heurte à deux contraintes : une faible diversité des plantes métallophytes et une méconnaissance des mécanismes de la tolérance au Pb.Dans ce contexte, l'objectif de mon travail de thèse a été de sélectionner une ou des plantes susceptibles d'entrer dans un programme de phytoremédiation et d'identifier des gènes impliqués dans la tolérance au Pb. Dans un premier temps, l'analyse des sols et des résidus miniers a révélé une importante contamination polymétallique du site d'étude. Des prospections floristiques ont ensuite permis d'identifier une plante de la famille des brassicacées, Hirschfeldia incana, prédominante sur les sites miniers pollués et qui accumule le Pb. L'accumulation du Pb chez H. incana a été confirmée en conditions contrôlées et une stratégie « gène candidat » a montré l'implication dans la tolérance au Pb de deux gènes, l'un codant pour une métallothionéine MT2a et l'autre pour un transporteur membranaire HMA4. Enfin, la comparaison des transcriptomes d'H. incana et d'A. thaliana a abouti à l'édification d'une liste de gènes candidats susceptibles d'être impliqués dans la tolérance au Pb. L'analyse fonctionnelle de quatre de ces gènes, codant pour une ferritine, une métallothionéine, une protéine fixatrice du cuivre et une défensine, a précisé leur rôle dans la tolérance au Pb.Exploited, and then abandoned, mining sites, in the oriental Morocco, have polluted the neighboring regions, by dispersion of mining wastes containing Pb. Facing this problem, it is necessary to develop phytomanagement programs. Nevertheless, these project realisations encountered two major constraints: weak metallophyte plant diversity and misunderstanding of Pb tolerance mechanisms. In this context, the objectif of my work was to select plants compatible with a phytoremediation program and to identify genes implicated in lead tolerance. Firstly, soil and mining waste analysis has revealed an important polymetallic pollution of the studied region. Then, floristic explorations had permitted to identify a plant of the brassicaceae family, Hirschfeldia incana, which is predominant on the polluted mining regions and accumulated Pb. Pb accumulation in H. incana was confirmed in controlled conditions and a candidate gene approach has shown the lead tolerance implication of two genes, one coding for a metallothionein (MT2A) and the other a membrane transporter (HMA4). Finally, the transcriptome comparison from H. incana and A. thaliana has generated a list of candidate genes putatively implicated in Pb tolerance. Functional analysis of four genes, coding a ferretin, a metallothionein, a copper binding protein and a defensin, has permitted to clarify their role in Pb tolerance

The Complete Genome Resource of Xanthomonas oryzae pv. oryzae CIX2779 Includes the First Sequence of a Plasmid for an African Representative of This Rice Pathogen

The bacterial plant pathogen Xanthomonas oryzae pv. oryzae is responsible for the foliar rice bacterial blight disease. Genetically contrasted, continent-specific, sublineages of this species can cause important damages to rice production both in Asia and Africa. We report on the genome of the CIX2779 strain of this pathogen, previously named NAI1 and originating from Niger. Oxford Nanopore long reads assembly and Illumina short reads polishing produced a genome sequence composed of a 4,725,792-bp circular chromosome and a 39,798-bp-long circular plasmid designated pCIX2779_1. The chromosome structure and base-level sequence are highly related to reference strains of African X. oryzae pv. oryzae and encode identical transcription activator-like effectors for virulence. Importantly, our in silico analysis strongly indicates that pCIX2779_1 is a genuine conjugative plasmid, the first indigenous one sequenced from an African strain of the X. oryzae species. [Graphic: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license

Characterization of a Casuarina glauca nodule-specific subtilisin-like protease gene, a homolog of Alnus glutinosa ag12

In search of plant genes expressed during early interactions between #Casuarina glauca and #Frankia, we have isolated and characterized a #C. glauca gene that has strong homology to subtilisin-like protease gene families of several plants including the actinorhizal nodulin gene ag12 of another actinorhizal plant, #Alnus glutinosa. Based on the expression pattern of cg12 in the course of nodule development, it represents an early actinorhizal nodulin gene. Our results suggest that subtilisin-like proteases may be a common element in the process of infection of plant cells by #Frankia in both Betulaceae (#Alnus glutinosa) and Casuarinaceae (#Casuarina glauca$) symbioses. (Résumé d'auteur