Selected isolates of Trichoderma gamsii induce different pathways of systemic resistance in maize upon Fusarium verticillioides challenge

The pink ear rot is one of the most damaging maize diseases, caused by the mycotoxigenic fungal pathogen, Fusarium verticillioides. The application of biological control agents, like antagonistic and/or resistance inducer microorganisms, is an option to reduce fungal infection and kernel contamination in a sustainable and environmentally friendly way. It is well known that Trichoderma species are non-pathogenic fungi able to antagonize plant pathogens and to induce systemic resistance in plants. The present work aimed to verify if Trichoderma spp., applied to maize kernels, affect the plant growth and induce systemic responses to F. verticillioides. Besides, the capability to reduce fumonisin concentration in liquid cultures was investigated. Two T. gamsii (IMO5 and B21), and one T. afroharzianum (B75) isolates, selected both for antagonism and for the ability to reduce root infections, significantly reduced the endophytic development of the stem-inoculated pathogen, compared to the control. The mechanisms of action appeared to be strain-specific, with IMO5 enhancing transcript levels of marker genes of Induced Systemic Resistance (ZmLOX10, ZmAOS, and ZmHPL) while B21 enhancing marker genes of Systemic Acquired Resistance (ZmPR1 and ZmPR5), as evinced by measuring their expression profiles in the leaves. Moreover, IMO5 promoted plant growth, while B21 was able to significantly reduce the fumonisin content in a liquid medium. The results of this work give new evidence that the seed application of T. gamsii is a promising tool for controlling F. verticillioides to be integrated with breeding and the adoption of good agricultural practices.

Isatis canescens is a rich source of glucobrassicin and other health-promoting compounds

BACKGROUND

Glucobrassicin (GBS), a glucosinolate contained in many brassica vegetables, is the precursor of chemopreventive compounds such as indole-3-carbinol. Large amounts of GBS would be needed to perform studies aimed at elucidating its role in the diet. This study was mainly undertaken to evaluate the flower buds of Isatis canescens as a source for GBS purification. In order to investigate the health-promoting potential of this species, glucosinolate, phenol and flavonoid content as well as the whole antioxidant capacity were also determined. Flower bud samples were collected in four localities around Mount Etna in Sicily, Italy, where I. canescens is widespread, as they are locally traditionally eaten.

RESULTS

I. canescens flower buds displayed high GBS concentrations, up to 60 µmol g(-1) dry weight. The purification method consisted of two chromatographic steps, which made it possible to obtain GBS with a purity of 92-95%, with a yield of 21 g kg(-1) . The total glucosinolates, phenols, flavonoids and antioxidant activity were considerable, with the southern locality showing the highest concentrations for all the phytochemicals.

CONCLUSION

I. canescens flower buds represent a naturally rich source of GBS, at a level suitable for its purification. Furthermore, flower bud consumption could provide an intake of health-promoting compounds, with possible antioxidant and chemopreventive properties.

A novel microplate-based screening strategy to assess the cellulolytic potential of Trichoderma strains

Bioconversion of lignocellulosic biomass to fuel requires a hydrolysis step to obtain fermentable sugars, generally accomplished by fungal enzymes. An assorted library of cellulolytic microbial strains should facilitate the development of optimal enzyme cocktails specific for locally available feedstocks. Only a limited number of strains can be simultaneously assayed in screening based on large volume cultivation methods, as in shake flasks. This study describes a miniaturization strategy aimed at allowing parallel assessment of large numbers of fungal strains. Trichoderma strains were cultivated stationary on microcrystalline cellulose using flat bottom 24-well plates containing an agarized medium. Supernatants obtained by a rapid centrifugation step of the whole culture plates were evaluated for extracellular total cellulase activity, measured as filter paper activity, using a microplate-based assay. The results obtained were consistent with those observed in shake-flask experiments and more than 300 Trichoderma strains were accordingly characterized for cellulase production. Five strains, displaying on shake-flasks at least 80% of the activity shown by the hyper-cellulolytic mutant Trichoderma Rut-C30, were correctly recognized by the screening on 24-well plates, demonstrating the feasibility of this approach. Cellulase activity distribution for the entire Trichoderma collection is also reported. One strain (T. harzianum Ba8/86) displayed the closest profile to the reference strain Rut-C30 in time course experiments. The method is scalable and addresses a major bottleneck in screening programs, allowing small-scale parallel cultivation and rapid supernatant extraction. It can also be easily integrated with high-throughput enzyme assays and could be suitable for automation.

Fluorescence quantitation of thyrocyte iodide accumulation with the yellow fluorescent protein variant YFP-H148Q/I152L

The thyroid gland accumulates iodide for the synthesis of thyroid hormones. The aim of the current study was to quantify iodide accumulation in cultured thyroid cells by live cell imaging using the halide-sensitive yellow fluorescent protein (YFP) variant YFP-H148Q/I152L. In vivo calibrations were performed in FRTL-5 thyrocytes to determine the sensitivity of YFP-H148Q/I152L to iodide. In the presence of ion-selective ionophores, YFP-H148Q/I152L fluorescence was suppressed by halides in a pH-dependent manner with 20-fold selectivity for iodide versus chloride and competition between the two halides. At a physiological pH of 7 and a chloride concentration of 15mM, the affinity constant of YFP-H148Q/I152L for iodide was 3.5mM. In intact FRTL-5 cells, iodide induced a reversible decrease in YFP-H148Q/I152L fluorescence. FRTL-5 cells concentrated iodide to 60 times the extracellular concentration. Iodide influx exhibited saturation kinetics with respect to extracellular iodide with a K(m) of 35 microM and a V(max) of 55 microM/s. Iodide efflux exhibited saturation kinetics with respect to intracellular iodide concentration with a K(m) of 2.2mM and a V(max) of 43 microM/s. The results of this study demonstrate the utility of YFP-H148Q/I152L as a sensitive and selective biosensor for the quantification of iodide accumulation in thyroid cells.

Cell-based imaging of sodium iodide symporter activity with the yellow fluorescent protein variant YFP-H148Q/I152L

The sodium iodide symporter (NIS) mediates iodide (I−) transport in the thyroid gland and other tissues and is of increasing importance as a therapeutic target and nuclear imaging reporter. NIS activity in vitro is currently measured with radiotracers and electrophysiological techniques. We report on the development of a novel live cell imaging assay of NIS activity using the I−-sensitive and genetically encodable yellow fluorescent protein (YFP) variant YFP-H148Q/I152L. In FRTL-5 thyrocytes stably expressing YFP-H148Q/I152L, I− induced a rapid and reversible decrease in cellular fluorescence characterized by 1) high affinity for extracellular I− (35 μM), 2) inhibition by the NIS inhibitor perchlorate, 3) extracellular Na+ dependence, and 4) TSH dependence, suggesting that fluorescence changes are due to I− influx via NIS. Individual cells within a population of FRTL-5 cells exhibited a 3.5-fold variation in the rate of NIS-mediated I− influx, illustrating the utility of YFP-H148Q/I152L to detect cell-to-cell difference in NIS activity. I− also caused a perchlorate-sensitive decrease in YFP-H148Q/I152L fluorescence in COS-7 cells expressing NIS but not in cells lacking NIS. These results demonstrate that YFP-H148Q/I152L is a sensitive biosensor of NIS-mediated I− uptake in thyroid cells and in nonthyroidal cells following gene transfer and suggest that fluorescence detection of cellular I− may be a useful tool by which to study the pathophysiology and pharmacology of NIS.

Silencing of the gene coding for the epsilon subunit of DNA polymerase III slows down the growth rate of Escherichia coli populations

Chromosome replication in Escherichia coli is accomplished by the multimeric enzyme DNA polymerase III; the relevance, in vivo, of the epsilon subunit (encoded by dnaQ) for processivity and fidelity of DNA polymerase III has been evaluated. To this aim, dnaQ has been conditionally silenced by means of in vivo expression of different antisense RNAs. Unexpectedly, the presence of the Shine-Dalgarno sequence is essential for the effectiveness of antisense constructs. Silencing of dnaQ induces a severe decrease in growth rate not paralleled by high mutation frequencies, suggesting that the epsilon subunit primarily affects the processivity of DNA polymerase III.