An antifungal effector from a plant-parasitic nematode modulates host fungal community composition and supports ecological fitness.

Host-associated microbiomes are increasingly recognized as key determinants of plant health, disease development, and ecosystem functioning. Plant pathogens, especially fungal pathogens, have been reported to secrete antimicrobial effectors to modulate the host microbiota and promote colonization. Plant-parasitic nematodes (PPNs) could also modulate host microbial communities, but the processes involved remain to be clarified. Here, we identify a secreted antifungal effector, BxylTLP6, from Bursaphelenchus xylophilus, the causal agent of pine wilt disease. BxylTLP6 degrades fungal cell walls and inhibits multiple plant-associated fungi, while the released oligoglucans serve as food-derived cues that guide nematode foraging toward fungal resources. In planta, silencing Bxyltlp6 significantly delayed disease progression. ITS-based mycobiome profiling revealed that BxylTLP6 modulates the pine endophytic fungal community by promoting Ascomycota, suppressing Basidiomycota, inhibiting wood-decaying fungi, and enriching pathogenic or parasitic taxa. These shifts are associated with enhanced nematode survival and pathogenicity. Our findings support the view that a TLP effector can modulate behavior and influence the host fungal microbiome, shedding light on how PPN may manipulate microbial environments to enhance their fitness.