The putative inositol transporter VdIPT1 negatively regulates Verticillium dahliae virulence: A cautionary example for cotton RNAi target selection

Upland cotton ( Gossypium hirsutum ), the world's dominant natural fiber crop, suffers severe yield and quality losses from Verticillium wilt. This highly destructive vascular disease, caused by the soilborne hemibiotrophic fungus Verticillium dahliae , poses a persistent threat to global cotton production. Nutrient transporters are increasingly recognized as candidate targets for innovative disease management, yet their functional roles and involvement in pathogenicity remain largely unexplored for non-canonical functions in V. dahliae . Here, we identified and functionally characterized VdIPT1 encoding a putative inositol transporter in V. dahliae . Deletion of VdIPT1 (Δ VdIPT1 ) unexpectedly promoted mycelial proliferation, conidiation capacity, and carbon/nitrogen assimilation, leading to enhanced virulence towards cotton seedlings. In agreement with fungal knockout phenotypes, both transient Host-Induced Gene Silencing (HIGS) and stable expression of VdIPT1 -RNAi constructs in cotton effectively silenced fungal VdIPT1 but compromised host defense rather than conferring disease resistance, resulting in exacerbated disease symptoms and elevated fungal biomass accumulation. Transcriptome profiling demonstrated that the impaired resistance in VdIPT1 -RNAi cotton was tightly linked to the transcriptional repression of core defense modules, particularly phenylpropanoid biosynthesis and plant–pathogen interaction signaling cascades. Our findings establish this putative inositol transporter VdIPT1 as a negative modulator of fungal virulence. Critically, silencing VdIPT1 is not a feasible HIGS-based resistance strategy. This work provides an important cautionary example, emphasizing that target genes must undergo thorough functional validation prior to their application in RNAi-mediated crop disease resistance breeding.