Graciela N. Pastorino

Incompatibility may not be the rule in the Sinorhizobium fredii–soybean interaction

Abstract In this work we confirmed that three Sinorhizobium fredii strains—USDA191, SMH12 and HH103—can nodulate and fix nitrogen on 40 soybean cultivars tested. Nitrogen-fixation was as in other nitrogen-fixing symbiosis the result of the bacterial-plant genome interactions. Based on our results, and those of others, we propose that compatibility is most probably the rule for the S. fredii –soybean symbiosis.

Identification of fast and slow growing rhizobia nodulating soybean (Glycine max [L.] Merr) by a multiplex PCR reaction.

Two DNA fragments, a 730-bp and a 900-bp fragment, one homologous to host cultivar specificity genes nolBT of Sinorhizobium fredii and the other one homologous to RSalpha, an insertion-like sequence present in Bradyrhizobium japonicum, were generated by polymerase chain reaction (PCR) with two pairs of primers. The amount of each fragment generated by the multiplex PCR was proportional to the amount of template DNA present. The amplification of the 900-bp RSalpha fragment was more sensitive, since it was amplified from a smaller amount of template DNA than the 730-bp nolBT fragment. By running the multiplex reaction in the presence of template DNA isolated from different sources, we confirmed that the reaction can discriminate between S. fredii, Bradyrhizobium japonicum and Sinorhizobium xinjiangensis.

The mitochondrial genome of the plantpathogenic fungus Stemphylium lycopersici uncovers a dynamic structure due to repetitive and mobile elements

Stemphylium lycopersici (Pleosporales) is a plant-pathogenic fungus that has been associated with a broad range of plant-hosts worldwide. It is one of the causative agents of gray leaf spot disease in tomato and pepper. The aim of this work was to characterize the mitochondrial genome of S. lycopersici CIDEFI-216, to use it to trace taxonomic relationships with other fungal taxa and to get insights into the evolutionary history of this phytopathogen. The complete mitochondrial genome was assembled into a circular double-stranded DNA molecule of 75,911 bp that harbors a set of 37 protein-coding genes, 2 rRNA genes (rns and rnl) and 28 tRNA genes, which are transcribed from both sense and antisense strands. Remarkably, its gene repertoire lacks both atp8 and atp9, contains a free-standing gene for the ribosomal protein S3 (rps3) and includes 13 genes with homing endonuclease domains that are mostly located within its 15 group I introns. Strikingly, subunits 1 and 2 of cytochrome oxidase are encoded by a single continuous open reading frame (ORF). A comparative mitogenomic analysis revealed the large extent of structural rearrangements among representatives of Pleosporales, showing the plasticity of their mitochondrial genomes. Finally, an exhaustive phylogenetic analysis of the subphylum Pezizomycotina based on mitochondrial data reconstructed their relationships in concordance with several studies based on nuclear data. This is the first report of a mitochondrial genome belonging to a representative of the family Pleosporaceae.

Nodulation and Delayed Nodule Senescence: Strategies of Two Bradyrhizobium Japonicum Isolates with High Capacity to Fix Nitrogen

The purpose of this work was to study further two Bradyrhizobium japonicum strains with high nitrogen-fixing capacity that were identified within a collection of approximately 200 isolates from the soils of Argentina. Nodulation and nitrogen-fixing capacity and the level of expression of regulatory as well as structural genes of nitrogen fixation and the 1-aminocyclopropane-1-carboxylate (ACC) deaminase gene of the isolates were compared with that of E109-inoculated plants. Both isolates of B. japonicum, 163 and 366, were highly efficient to fix nitrogen compared to commercial strain E109. Isolate 366 developed a higher number and larger biomass of nodules and because of this fixed more nitrogen. Isolate 163 developed the same number and nodule biomass than E109. However, nodules developed by isolate 163 had red interiors for a longer period, had a higher leghemoglobin content, and presented high levels of expression of acdS gene, that codes for an ACC deaminase. In conclusion, naturalized rhizobia of the soils of Argentina hold a diverse population that might be the source of highly active nitrogen-fixing rhizobia, a process that appears to be based on different strategies.

Ensifer (Sinorhizobium) fredii Interacted More Efficiently than Bradyrhizobium japonicum with Soybean

Fil: Pastorino, Graciela Noemi. Universidad Nacional de La Plata; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina