P-651 - Nuclear localization sequence of MoHTR1, a Magnaporthe oryzae effector, for transcriptional reprogramming of immunity genes in rice

Plant pathogens deploy nuclear effector into host cell nuclei to manipulate host immunity. While several fungal nuclear effectors have recently been identified, the molecular mechanisms governing their nuclear import, particularly the role of nuclear localization signals (NLS), remain largely unclear. In our previous work, we characterized MoHTR1, a nuclear effector from the rice blast fungus Magnaporthe oryzae, which localizes to rice nuclei but not to fungal nuclei. Here, we identified the core NLS motif (RxKK) as essential for the nuclear localization of MoHTR1. This motif mediates its translocation into rice nuclei via interaction with host importin α. Remarkably, MoHTR1 NLS also facilitates the nuclear import of other M. oryzae cytoplasmic effectors when fused to them, underscoring its transport-driving capacity. Furthermore, both additional effector candidates from M. oryzae and native rice proteins containing the RxKK motif also localize to the nucleus, highlighting the crucial role of RxKK in this process. We also reveal that SUMOylation enhances the stability of MoHTR1 and promotes its nuclear translocation. Critically, the RxKK motif is indispensable for the pathogenicity of M. oryzae, enabling MoHTR1 to reprogram host immunity-related gene expression. Together, our findings provide insights into the significance of plant-specific NLS on fungal nuclear effectors and its role in plant-pathogen interactions.