Protoplast formation and DNA-mediated transformation of Fusarium culmorum to hygromycin B resistance

Vib-PT, an Aromatic Prenyltransferase Involved in the Biosynthesis of Vibralactone from Stereum vibrans

Vibralactone, a hybrid compound derived from phenols and a prenyl group, is a strong pancreatic lipase inhibitor with a rare fused bicyclic β-lactone skeleton. Recently, a researcher reported a vibralactone derivative (compound C1) that caused inhibition of pancreatic lipase with a half-maximal inhibitory concentration of 14 nM determined by structure-based optimization, suggesting a potential candidate as a new antiobesity treatment. In the present study, we sought to identify the main gene encoding prenyltransferase in Stereum vibrans, which is responsible for the prenylation of phenol leading to vibralactone synthesis. Two RNA silencing transformants of the identified gene (vib-PT) were obtained through Agrobacterium tumefaciens-mediated transformation. Compared to wild-type strains, the transformants showed a decrease in vib-PT expression ranging from 11.0 to 56.0% at 5, 10, and 15 days in reverse transcription-quantitative PCR analysis, along with a reduction in primary vibralactone production of 37 to 64% at 15 and 21 days, respectively, as determined using ultra-high-performance liquid chromatography-mass spectrometry analysis. A soluble and enzymatically active fusion Vib-PT protein was obtained by expressing vib-PT in Escherichia coli, and the enzyme's optimal reaction conditions and catalytic efficiency (K_m /k _cat) were determined. In vitro experiments established that Vib-PT catalyzed the C-prenylation at C-3 of 4-hydroxy-benzaldehyde and the O-prenylation at the 4-hydroxy of 4-hydroxy-benzenemethanol in the presence of dimethylallyl diphosphate. Moreover, Vib-PT shows promiscuity toward aromatic compounds and prenyl donors.IMPORTANCE Vibralactone is a lead compound with a novel skeleton structure that shows strong inhibitory activity against pancreatic lipase. Vibralactone is not encoded by the genome directly but rather is synthesized from phenol, followed by prenylation and other enzyme reactions. Here, we used an RNA silencing approach to identify and characterize a prenyltransferase in a basidiomycete species that is responsible for the synthesis of vibralactone. The identified gene, vib-PT, was expressed in Escherichia coli to obtain a soluble and enzymatically active fusion Vib-PT protein. In vitro characterization of the enzyme demonstrated the catalytic mechanism of prenylation and broad substrate range for different aromatic acceptors and prenyl donors. These characteristics highlight the possibility of Vib-PT to generate prenylated derivatives of aromatics and other compounds as improved bioactive agents or potential prodrugs.

Formation and regeneration of protoplasts in Sclerotium rolfsii ATCC 201126

AIMS

Different cultural conditions for forming and reverting protoplasts were systematically studied to establish a rapid and efficient protocol for Sclerotium rolfsii ATCC 201126.

METHODS AND RESULTS

Osmotic stabilizer, lytic enzymes and mycelial age were the main factors influencing protoplast yields. An optimized protocol involving 1-h hydrolysis of 45-h-old mycelium with Trichoderma harzianum enzymes in a 1 : 1 (w/w) biomass : enzyme ratio and 0.6 mol l-1 MgSO4 as osmotic stabilizer was designed to produce approx. 2 x 109 protoplasts per gram biomass dry weight, with 99% viability. Differences on the lytic activity between batches of commercial enzymes were clearly evidenced. Protoplast release was highly efficient showing no remaining cell wall material as witnessed by fluorescent brightener 28. Up to 26% of purified protoplasts developed into the typical filamentous form after 50 h of incubation on 0.6 mol l-1 sucrose agar media.

CONCLUSIONS

The methodology herein proposed allowed a rapid, inexpensive and efficient protoplast production. Optimum yields were higher or in the order of that elsewhere reported for other S. rolfsii strains and the required lytic time was significantly shorter. Purified protoplasts successfully reverted to the filamentous morphology.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present research reports the former protocol for the isolation and reversion of protoplasts in S. rolfsii ATCC 201126 providing key factors to ensure optimum results. In addition, the described procedure constitutes a starting point for downstream genetic manipulation.

Agrobacterium and PEG-mediated transformation of the phytopathogen Venturia inaequalis

We report the development of two new transformation systems, polyethylene glycol (PEG)-mediated transformation of protoplasts and Agrobacterium tumefaciens-mediated transformation of mycelium, for the filamentous ascomycete Venturia inaequalis. New binary vectors have been created for the latter. Although transformation was initially achieved using a PEG-mediated method, this was superseded by the A. tumefaciens-mediated approach. The advantages of the latter include: ease of the protocol, no requirement for protoplasts; higher transformation efficiency; and single-site integration. A comparison between the two transformation methods is presented.