A nematode-trapping fungus orchestrates polarity cues, septins, and NOX signaling for trap formation.

Reprogramming cell morphogenesis in response to environmental cues is fundamental to microbial adaptation and survival. The nematode-trapping fungus (NTF) Arthrobotrys oligospora exemplifies this plasticity by developing adhesive traps to capture nematodes. However, mechanisms underlying trap morphogenesis and host invasion remain unclear. Using live-cell imaging, genetics, and functional assays, we show trap morphogenesis proceeds through localized redirection of hyphal growth followed by site-specific hyphal fusion, whereas infection development involves a transition from isotropic infection bulb expansion to multipolar invasive growth. These transitions are coordinated by the reorganization of conserved polarity proteins, asymmetric septin localization at the trap cell inner rim, and actin remodeling. Nematode-induced Nox1 signaling is required to recruit polarity and cytoskeletal machinery to the trap cell fusion site. Together, these findings establish NTF as a powerful model for understanding how conserved morphogenetic machinery drives the transition from linear hyphae to hyphal loops to trap nematodes.