The fungal phytotoxin Sphaeropsidin A from Diplodia cupressi induces oxidative stress and autophagy in Arabidopsis thaliana

The pimarane diterpene Sphaeropsidin A (SphA) is the main phytotoxin produced by the necrotrophic fungus Diplodia cupressi L., the causal agent of cypress canker. It has emerged as a highly versatile molecule due to its unique chemical structure and a remarkably broad spectrum of biological activities, which support its use as an eco-friendly herbicide, pesticide, or antibiotic against drug-resistant human pathogens. Although in recent years SphA has gained attention, especially for its potent anticancer properties and its ability to overcome multidrug resistance in human cells by targeting the regulatory volume increase process, its molecular mechanism of action in plants remains largely uncharacterized. This study investigates the physiological and biochemical effects of SphA using Arabidopsis thaliana plants and protoplasts as a model system. Our results demonstrate that SphA treatment significantly inhibits plant growth and induces leaf chlorosis, ion leakage, ROS accumulation and cell death. Subcellular analysis using confocal microscopy revealed that SphA targets multiple organelles; it hampers the functionality of mitochondria and chloroplasts, leading to the overproduction of reactive oxygen species and the disgregation of the tonoplast membrane, causing programmed cell death and autophagy. This study provides a deeper understanding of the cellular targets of SphA in plants, supporting its potential development as a nature-inspired bioherbicide.