The Signal Peptidase MoSpc2 Orchestrates Fungal Development, Protein Secretion and Pathogenicity in Magnaporthe oryzae.

The signal peptidase complex (SPC) is a crucial membrane enzyme complex involved in the process of protein secretion and maturation in both prokaryotic and eukaryotic cells. SPC is responsible for the cleavage of N-terminal signal sequences from nascent proteins, a sequence of amino acids that directs the newly synthesized protein to the secretory pathway. The yeast SPC is composed of four subunits: Spc1, Spc2, Spc3, and Sec11. To understand how SPC functions in the fungal plant pathogen, we identified the SPC component gene MoSPC2 and characterized its functions in M. oryzae. Through measuring the colony diameter of the ΔMospc2 mutant and control strains on culture medium plates, quantifying conidia production, observing conidial morphology, and assessing pathogenicity on rice and barley plants, we found that MoSpc2 contributes to fungal growth, asexual development, and pathogenicity. Since host-derived reactive oxygen species (ROS) are crucial for rice to defend against M. oryzae, we further investigated the role of MoSpc2 in ROS modulation. Our results indicate that MoSpc2 plays a pivotal role in suppressing the accumulation of ROS and regulating the activities of extracellular peroxidases and laccases. Notably, MoSpc2 mediates the accumulation and secretion of the effector protein MoSlp1. Furthermore, using affinity purification, we discovered MoSpc2-interacting proteins and identified potential SPC interactors. These candidates provide a foundation for future mechanistic studies aimed at elucidating their functional roles in SPC complex assembly and pathogenic regulation. Our results highlight the significance of the SPC component gene MoSPC2 involvement in fungal development and pathogenicity and widen our understanding of the connections between the SPC and fungal pathogenesis.