Insights into the Antifungal Properties of Myxobacteria Outer Membrane β-1,6-Glucanase

Neg1 overexpression in Trichoderma harzianum T4 enhanced its ability to produce spores and antagonistic activity against phytopathogenic fungi

Trichoderma harzianum T4 is a soil fungus that plays an important role in the biological control of plant diseases. The aim of this study was to functionally characterize the β-1,6-glucanase gene Neg1 in T. harzianum T4 and to investigate the effect of its overexpression on biocontrol traits, especially antagonism against pathogenic fungi. We found that overexpression of Neg1 did not affect growth of T. harzianum but enhanced sporulation of T. harzianum T4 cultures. Generally, spores are closely related to the defense ability of defense fungi and can assist their proliferation and improve their colonization ability. Secondly, overexpression of Neg1 also increased the secretion level of various hydrolytic enzymes and enhanced the antagonistic ability against phytopathogenic fungi of Fusarium spp. The results suggest that Neg1 is a key gene for improving the biocontrol effect of T. harzianum T4, which contributes to a better understanding of the mechanism of action of T. harzianum T4 as a fungal biocontrol agent.

Functional analysis of a novel endo-β-1,6-glucanase MoGlu16 and its application in detecting cell wall β-1,6-glucan of Magnaporthe oryzae

As an essential component of the fungal cell wall, β-1,6-glucan has an important role in the growth and development of fungi, but its distribution has not been investigated in Magnaporthe oryzae. Here, a novel β-1,6-glucanase from M. oryzae, MoGlu16, was cloned and expressed in Pichia pastoris. The enzyme was highly active on pustulan, with a specific activity of 219.0 U/mg at pH 5.0 and 50°C, and showed great selectivity for continuous β-1,6-glycosidic bonding polysaccharides. Based on this, β-1,6-glucan was selectively visualized in the vegetative hyphae, conidia and bud tubes of M. oryzae using a hydrolytically inactive GFP-tagged MoGlu16 with point mutations at the catalytic position (His-MoGlu16E236A-Gfp). The spore germination and appressorium formation were significantly inhibited after incubation of 105/ml conidia with 0.03 μg/μl MoGlu16. Mycelia treated with MoGlu16 produced reactive oxygen species and triggered the cell wall integrity pathway, increasing the expression levels of genes involved in cell wall polysaccharide synthesis. These results revealed that MoGlu16 participated in the remodeling of cell wall in M. oryzae, laying a foundation for the analysis of cell wall structure.

The Development of Aspergillus flavus and Biosynthesis of Aflatoxin B1 are Regulated by the Golgi-Localized Mn2+ Transporter Pmr1

Microorganisms rely on diverse ion transport and trace elements to sustain growth, development, and secondary metabolism. Manganese (Mn2+) is essential for various biological processes and plays a crucial role in the metabolism of human cells, plants, and yeast. In Aspergillus flavus, we confirmed that Pmr1 localized in cis- and medial-Golgi compartments was critical in facilitating Mn2+ transport, fungal growth, development, secondary metabolism, and glycosylation. In comparison to the wild type, the Δpmr1 mutant displayed heightened sensitivity to environmental stress, accompanied by inhibited synthesis of aflatoxin B1, kojic acid, and a substantial reduction in pathogenicity toward peanuts and maize. Interestingly, the addition of exogenous Mn2+ effectively rectified the developmental and secondary metabolic defects in the Δpmr1 mutant. However, Mn2+ supplement failed to restore the growth and development of the Δpmr1Δgdt1 double mutant, which indicated that the Gdt1 compensated for the functional deficiency of pmr1. In addition, our results showed that pmr1 knockout leads to an upregulation of O-glycosyl-N-acetylglucose (O-GlcNAc) and O-GlcNAc transferase (OGT), while Mn2+ supplementation can restore the glycosylation in A. flavus. Collectively, this study indicates that the pmr1 regulates Mn2+ via Golgi and maintains growth and metabolism functions of A. flavus through regulation of the glycosylation.