Exploring dynamic changes of fungal cellular components during nanoemulsion treatment by multivariate microRaman imaging.

Recently, essential oils (EO) have gained a lot of interest for use as antifungal agent in food and agricultural industry and extensive research is ongoing to understand their mode of action. However, the exact mechanism is not yet elucidated. Here, we integrated spectral unmixing and Raman microspectroscopy imaging to unveil the antifungal mechanism of green tea EO based nanoemulsion (NE) against Magnaporthe oryzae. The dramatic change in protein, lipid, adenine, and guanine bands indicate that NE has a significant impact on the protein, lipid and metabolic processes of purine. The results also demonstrated that the NE treatment caused damage to fungal hyphae by inducing a physical injury leading to cell wall damage and loss of integrity. Our study shows that MCR-ALS (Multivariate Curve Resolution-Alternating Least Squares) and N-FINDR (N-finder algorithm) Raman imaging could serve as a suitable complementary package to the traditional methods, for revealing the antifungal mechanism of action of EO/NE.

Preparation and characterization of a novel green tea essential oil nanoemulsion and its antifungal mechanism of action against Magnaporthae oryzae.

Blast is one of the most devastating fungal diseases of rice caused by Magnaporthe oryzae. Plant essential oil (EO) can function as antifungal agents and are regarded as a safe and acceptable method for plant disease control. However, EOs are unstable and hydrophobic, which limits its use. In the present study, we aimed for the preparation and characterization of a nanoemulsion (NE) from green tea essential oil (GTO) by ultrasonication method and determined the antifungal activity of NE onM. oryzae. The particle size and zeta potential of the NE were 86.98 nm and -15.1 mV, respectively. The chemical composition and functional groups of GTO and NE were studied by using GC-MS analysis, portable Raman spectroscopy, and FTIR coupled with chemometric analysis. GC-MS analysis showed the major components in GTO and NE were n-Hexyl cinnamaldehyde and L-α-Terpineol. Both GTO and NE showed good antioxidant activity and total phenol content. Moreover, the NE showed good antifungal activity againstM. oryzae which was further confirmed by scanning electron microscopy (SEM) examination. Also, confocal Raman micro-spectroscopy (CRM) revealed the antifungal mechanism of GTO and NE on M. oryzae which proves the cell damage. To the best of our knowledge, this is the first study on the antifungal activity of GTO and NE against M. oryzae and also the use of CRM for the evaluation of the chemical changes in single fungal hyphae in a holistic approach. This study suggests that the prepared NE could be a potential candidate for use as a substitute for synthetic fungicides.

PoMet3 and PoMet14 associated with sulfate assimilation are essential for conidiogenesis and pathogenicity in Pyricularia oryzae.

Pyricularia oryzae is the causal agent of blast disease on staple gramineous crops. Sulphur is an essential element for the biosynthesis of cysteine and methionine in fungi. Here, we targeted the P. oryzae PoMET3 encoding the enzyme ATP sulfurylase, and PoMET14 encoding the APS (adenosine-5'-phosphosulphate) kinase that are involved in sulfate assimilation and sulphur-containing amino acids biosynthesis. In P. oryzae, deletion of PoMET3 or PoMET14 separately results in defects of conidiophore formation, significant impairments in conidiation, methionine and cysteine auxotrophy, limited invasive hypha extension, and remarkably reduced virulence on rice and barley. Furthermore, the defects of the null mutants could be restored by supplementing with exogenous cysteine or methionine. Our study explored the biological functions of sulfur assimilation and sulphur-containing amino acids biosynthesis in P. oryzae.

Piriformospora indica promotes growth, seed yield and quality of Brassica napus L.

In current scenario, crop productivity is being challenged by decreasing soil fertility. To cope up with this problem, different beneficial microbes are explored to increase the crop productivity with value additions. In this study, Brassica napus L., an important agricultural economic oilseed crop with rich source of nutritive qualities, was interacted with Piriformospora indica, a unique root colonizing fungus with wide host range and multifunctional aspects. The fungus-treated plants showed a significant increase in agronomic parameters with plant biomass, lodging-resistance, early bolting and flowering, oil yield and quality. Nutritional analysis revealed that plants treated by P. indica had reduced erucic acid and glucosinolates contents, and increased the accumulation of N, Ca, Mg, P, K, S, B, Fe and Zn elements. Low erucic acid and glucosinolates contents are important parameters for high quality oil, because oils high in erucic acid and glucosinolates are considered undesirable for human nutrition. Furthermore, the expression profiles of two encoding enzyme genes, Bn-FAE1 and BnECR, which are responsible for regulating erucic acid biosynthesis, were down-regulated at mid- and late- life stages during seeds development in colonized plants. These results demonstrated that P. indica played an important role in enhancing plant growth, rapeseed yield and quality improvement of B. napus.

Bioactive metabolites from Phoma species, an endophytic fungus from the Chinese medicinal plant Arisaema erubescens.

Through bioassay-guided fractionation, the EtOAc extract of a culture broth of the endophytic fungus Phoma species ZJWCF006 in Arisaema erubescens afforded a new α-tetralone derivative, (3S)-3,6,7-trihydroxy-α-tetralone (1), together with cercosporamide (2), ß-sitosterol (3), and trichodermin (4). The structures of compounds were established on the basis of spectroscopic analyses. Compounds 1, 2, and 3 were obtained from Phoma species for the first time. Additionally, the compounds were subjected to bioactivity assays, including antimicrobial activity, against four plant pathogenic fungi (Fusarium oxysporium, Rhizoctonia solani, Colletotrichum gloeosporioides, and Magnaporthe oryzae) and two plant pathogenic bacteria (Xanthomonas campestris and Xanthomonas oryzae), as well as in vitro antitumor activities against HT-29, SMMC-772, MCF-7, HL-60, MGC80-3, and P388 cell lines. Compound 1 showed growth inhibition against F. oxysporium and R. solani with EC50 values of 413.22 and 48.5 µg/mL, respectively. Additionally, compound 1 showed no cytotoxicity, whereas compound 2 exhibited cytotoxic activity against the six tumor cell lines tested, with IC50 values of 9.3 ± 2.8, 27.87 ± 1.78, 48.79 ± 2.56, 37.57 ± 1.65, 27.83 ± 0.48, and 30.37 ± 0.28 µM, respectively. We conclude that endophytic Phoma are promising sources of natural bioactive and novel metabolites.