Ustiloxins as Emerging Contaminants in Rice Agroecosystems: Environmental Occurrence, Ecotoxicological Impacts, and...

Ustiloxins are toxic cyclic peptides produced by the rice false smut fungus Ustilaginoidea virens. False smut disease turns rice grains into yellow-orange spores later turned into greenish-black smut balls, significantly reducing yield and grain quality. Due to their hydrophilic nature ustiloxins leach from spore balls and contaminate paddy soil, water, and rice products. They block eukaryotic cell division by binding tubulin and inhibit microtubule polymerization. This review provides information on advances in ustiloxin biology and control. It summarizes ribosomally synthesized and post-translationally modified peptides (RiPPs) biosynthesis and recent insights into pathway genes, regulatory networks including target of rapamycin (TOR) signaling, and comparative fungal genomics. Environmental occurrence is reviewed with emphasis on persistence in soil, water and translocation into rice grains. Ecotoxicological evidence is consolidated, spanning phytotoxicity, effects on beneficial microbes, aquatic organisms, and mammalian toxicity supported by in vivo and mechanistic studies. Progress in detection is outlined with improved LC-MS/MS, immunoassays, and emerging biosensors for field diagnostics. Management strategies are evaluated, including resistant cultivars, disease forecasting, fungicidal and biological controls, and post-harvest detoxification via enzymatic and physical approaches. A dedicated risk assessment discusses human dietary exposure, regulatory status, and the need for maximum limits. The review concludes by highlighting research priorities such as multi-omics, spread modeling, and biotechnological interventions, to close key knowledge gaps and enable effective monitoring and mitigation toward an ustiloxin-free rice agroecosystem.