Descripción: Fil:González, N.S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Removal of the poly(A) tail is the first step in the degradation of many eukaryotic mRNAs. In metazoans and yeast, the Ccr4/Caf1/Not complex has the predominant deadenylase activity, while the Pan2/Pan3 complex may trim poly(A) tails to the correct size, or initiate deadenylation. In trypanosomes, turnover of several constitutively-expressed or long-lived mRNAs is not affected by depletion of the 5'-3' exoribonuclease XRNA, but is almost completely inhibited by depletion of the deadenylase CAF1. In contrast, two highly unstable mRNAs, encoding EP procyclin and a phosphoglycerate kinase, PGKB, accumulate when XRNA levels are reduced. We here show that degradation of EP mRNA was partially inhibited after CAF1 depletion. RNAi-targeting trypanosome PAN2 had a mild effect on global deadenylation, and on degradation of a few mRNAs including EP. By amplifying and sequencing degradation intermediates, we demonstrated that a reduction in XRNA had no effect on degradation of a stable mRNA encoding a ribosomal protein, but caused accumulation of EP mRNA fragments that had lost substantial portions of the 5' and 3' ends. The results support a model in which trypanosome mRNAs can be degraded by at least two different, partially independent, cytoplasmic degradation pathways attacking both ends of the mRNA. © 2009 The Author(s).

Descripción: Sinorhizobium meliloti is a symbiotic nitrogen-fixing bacterium that elicits nodule formation on roots of alfalfa plants. S. meliloti produces two exopolysaccharides (EPSs), termed EPS I and EPS II, that are both able to promote symbiosis. EPS I and EPS II are secreted in two major fractions that reflect differing degrees of subunit polymerization, designated high- and low-molecularweight fractions. We reported previously that EPSs are crucial for autoaggregation and biofilm formation in S. meliloti reference strains and isogenic mutants. However, the previous observations were obtained by use of "domesticated" laboratory strains, with mutations resulting from successive passages under unnatural conditions, as has been documented for reference strain Rm1021. In the present study, we analyzed the autoaggregation and biofilm formation abilities of native S. meliloti strains isolated from root nodules of alfalfa plants grown in four regions of Argentina. 16S rRNA gene analysis of all the native isolates revealed a high degree of identity with reference S. meliloti strains. PCR analysis of the expR gene of all the isolates showed that, as in the case of reference strain Rm8530, this gene is not interrupted by an insertion sequence (IS) element. A positive correlation was found between autoaggregation and biofilm formation abilities in these rhizobia, indicating that both processes depend on the same physical adhesive forces. Extracellular complementation experiments using mutants of the native strains showed that autoaggregation was dependent on EPS II production. Our results indicate that a functional EPS II synthetic pathway and its proper regulation are essential for cell-cell interactions and surface attachment of S. meliloti. © 2012, American Society for Microbiology.

Descripción: Thelonectria is a recently established genus of common and ubiquitous fungi on woody hosts, previously placed in the genus Neonectria. Thelonectria coronata and T. veuillotiana occur sympatrically in tropical, subtropical and temperate regions. Previous taxonomic studies including T. coronata and T. veuillotiana suggested these fungi could represent species complexes; however, the morphological features used to define species exhibited few differences useful for testing this hypothesis. To assess the status of T. coronata and T. veuillotiana, phylogenetic analyses of six genomic regions were combined with a morphological examination of specimens. A multigene phylogeny reconstructed with maximum parsimony, maximum likelihood and Bayesian approaches identified five phylogenetic groups in T. coronata and six in T. veuillotiana. As is common for cryptic species, unequivocal diagnostic morphological characters could not be identified; however, average values of morphological traits correspond to the phylogenetic groups. An increased number of nonsynonymous/ synonymous substitutions in the b-tubulin gene and a decreased or absent production of conidia were detected within the T. coronata complex, possibly indicating the homothallic nature of these isolates. T. coronata and T. veuillotiana and related species are described and illustrated here; a dichotomous key to all species is provided. © 2012 by The Mycological Society of America.