3-Methylpentanoic acid from Bacillus safensis suppresses wheat blast disease by targeting UDP-glucose 4-epimerase

Abstract

Wheat blast, caused by Magnaporthe oryzae Triticum (MoT), is a devastating disease threatening global food security. Current reliance on chemical fungicides is unreliable due to the development of resistant MoT populations, highlighting the need for safe and eco-friendly alternatives. Naturally occurring volatile organic compounds (VOCs) possess potent antifungal potential thereby inhibiting phytopathogen. In this study, we investigated the fungicidal potential of 3-methylpentanoic acid (3-MP), a VOC produced by Bacillus safensis and also found in snake-fruit aroma, on MoT pathogen. In vitro assays revealed dose-dependent inhibition of MoT mycelial growth, conidiogenesis, conidial germination, and appressorium formation, with complete suppression achieved at 100-125 {micro}M. Detached leaf, seedling, and spike assays demonstrated robust preventive and curative protection, highlighting translational potential under field conditions. Mechanistic investigations showed that 3-MP compromises membrane integrity, as confirmed by fluorescein diacetate staining, and targets UDP-glucose 4-epimerase (UGE), a key enzyme required for galactose metabolism and cell wall integrity in fungi. Molecular dynamics simulations revealed stable binding of 3-MP within the NAD-associated Rossmann fold of UGE, sterically blocking substrate access and perturbing NAD orientation. RT-PCR gene expression analysis corroborated this model, showing early induction followed by repression of UGE expression, consistent with collapse of UDP-glucose metabolism and impaired cell wall biosynthesis. This study for the first time identified 3-MP as a natural inhibitor of UGE and provided new insight into the antifungal mechanism of the compound, highlighting its potential for integrated wheat blast management. ImportanceWheat blast, caused by Magnaporthe oryzae Triticum (MoT), poses a catastrophic threat to global food security, particularly in South America, Africa, and South Asia. With MoT rapidly developing resistance to conventional chemical fungicides, there is an urgent need for sustainable, eco-friendly alternatives. Our study identifies 3-methylpentanoic acid (3-MP), a volatile organic compound produced by Bacillus safensis, as a potent antifungal agent against MoT. We demonstrate that 3-MP inhibits multiple life stages of the pathogen, including mycelial growth, conidiation, and appressorium formation. Furthermore, we provide molecular insights through molecular docking and MD simulations, identifying UDP-glucose 4-epimerase as a likely target of 3-MP. By revealing a dual-action (preventive and curative) natural compound and its potential mechanism, this work offers a promising blueprint for developing bio-based fungicides to combat devastating plant diseases while reducing the environmental footprint of agriculture.