Structural insights into interaction of maize lipoxygenase ZmLox3 with Ustilago maydis effector Rip1

Lipoxygenases (LOXs) are ubiquitous enzymes in plants and play pivotal roles in various plant physiological processes, including plant immunity. The biotrophic fungus Ustilago maydis secretes effector Rip1 to target Zea mays lipoxygenase 3 (ZmLox3), which acts as a negative modulator of extracellular ROS burst. This interaction suppresses ROS production in maize, but the molecular interaction mechanisms underlying effector-mediated lipoxygenase regulation remain elusive. In this study, we obtained the crystal structure of ZmLox3, revealing a conserved β-barrel domain in its amino-terminal domain and iron-binding site and substrate-binding pocket in carboxy-terminal domain. The AlphaFold3-generated complex model of Zmlox3 with Rip1 demonstrates that critical residue R43 of Rip1 stabilizes the interaction interface by forming the hydrogen bond network with the side chains of ZmLox3 residues S274, D333, and E772. Furthermore, Rip1 enhances ZmLox3 enzymatic activity, thereby reducing maize susceptibility to U. maydis infection. This study provides insights into the interaction between a pathogen effector and a host susceptibility protein, proposing a mechanistic basis for improving maize resistance breeding through rational modification of susceptibility genes.