Dematophora necatrix (syn. Rosellinia necatrix ), a fungal pathogen causing white root rot in trees, dies when exposed to 35 °C for more than 2 days. This study aimed to elucidate the mechanisms underlying fungal death under non-lethal heat conditions in the presence of soil microbes, testing the hypothesis that heat stress in D. necatrix is a trigger. After treatment at 35°C for 2–12 h, correlative analysis was conducted using one mycelium of D. necatrix (W562) for gene expression, growth recovery, and competition ability against the hyphosphere fungus Taralomyces pinophilus (TAi6s), and another analysis for growth recovery, vital staining, and ultrastructural observation. All samples fell into one of two phenotypes: regrowth on 1-day post-incubation (dpi) and W562 dominance, or regrowth on 2 dpi and TAi6s dominance. The mRNA data showed that the control (25 °C) formed a single cluster, whereas the heated samples formed four clusters, regardless of the treatment duration. The control and three clusters exhibited the former phenotypes, whereas the last cluster exhibited the latter. Cluster B, representing the 1 dpi phenotype, upregulated autophagy- and DNA repair-related genes, showing phagophores, suggesting an autophagy condition. In contrast, cluster Db, the 2 dpi phenotype, upregulated antioxidant and apoptosis-related genes (MCA1, but not AIF1) and exhibited outer nuclear membrane swelling and heterochromatin aggregation. These results suggest that autophagy is for survival, whereas pre-apoptotic or more severe stress levels in D. necatrix play a key role in synergistic cell death.
Nguyen et al. (Fri,) studied this question.