Differential tolerance of high manganese among rapeseed genotypes

Cultivation of crop cultivars resistant to high soil manganese (Mn) may reduce the negative effects of Mn toxicity on crop yield. Three studies were carried out to select Brassica genotypes (B. napus and B. rapa) resistant to high Mn concentration and to characterise the nature of any Mn resistance found. In Experiment 1, 33 B. napus and nine B. rapa genotypes were screened in a sub-irrigated nutrient solution system. Based on visual symptoms and plant size, single plants were identified with resistance to high Mn from within cultivars of four B. napus and one B. rapa. Resistance was also identified in one B. napus doubled haploid genotype. In Experiment 2, a genotype resistant to high Mn and two genotypes (progenies from Experiment 1) sensitive to high Mn were exposed to eight Mn concentrations (9–500 M) for 2 weeks in nutrient solution. The relative shoot weight (RSW) and the relative root weight (RRW) of the genotype resistant to Mn were significantly greater at 100 M Mn than both genotypes sensitive to high Mn; the sensitive genotypes reacted similarly. The three genotypes had similar tissue Mn contents and the elevated Mn tissue contents did not induce deficiencies of Mg or Fe. In Experiment 3, 12 genotypes (progenies from Experiment 1) were screened in nutrient solution at 9 M Mn and with an additional 125 M Mn. The RRW and RSW of the genotypes ranged from 35 to 114 and 39 to 94%, respectively. All the selections sensitive to high Mn had a RSW <60% and thus were confirmed to be Mn sensitive, while all the selections resistant to Mn had a RSW >70% and thus were confirmed as Mn resistant. This evidence confirmed the availability of rapeseed germplasm resistant to Mn toxicity with an ability to withstand high content of Mn through internal tissue tolerance. Also, the observed Mn tolerance in this material is genetically controlled and not an artifact of our screening assays.     

A family 13 thioesterase isolated from an activated sludge metagenome: Insights into aromatic compounds metabolism

Activated sludge is produced during the treatment of sewage and industrial wastewaters. Its diverse chemical composition allows growth of a large collection of microbial phylotypes with very different physiologic and metabolic profiles. Thus, activated sludge is considered as an excellent environment to discover novel enzymes through functional metagenomics, especially activities related with degradation of environmental pollutants. Metagenomic DNA was isolated and purified from an activated sludge sample. Metagenomic libraries were subsequently constructed in Escherichia coli. Using tributyrin hydrolysis, a screening by functional analysis was conducted and a clone that showed esterase activity was isolated. Blastx analysis of the sequence of the cloned DNA revealed, among others, an ORF that encodes a putative thioesterase with 47–64% identity to GenBank CDS reported genes, similar to those in the hotdog fold thioesterase superfamily. On the basis of its amino acid similarity and its homology‐modelled structure we deduced that this gene encodes an enzyme (ThYest_ar) that belongs to family TE13, with a preference for aryl‐CoA substrates and a novel catalytic residue constellation. Plasmid retransformation in E. coli confirmed the clone's phenotype, and functional complementation of a paaI E. coli mutant showed preference for phenylacetate over chlorobenzene as a carbon source. This work suggests a role for TE13 family thioesterases in swimming and degradation approaches for phenyl acetic acid. Proteins 2017; 85:1222–1237. © 2017 Wiley Periodicals, Inc.