The Rab7 C-terminal intrinsically disordered region is a key determinant of development and pathogenicity in Aspergillus flavus.

Abstract

Rab7 GTPases coordinate late endosome maturation, vesicle trafficking, and vacuole biogenesis across eukaryotes, yet the functional contribution of the Rab7 C-terminal tail to organismal physiology remains incompletely defined. Here we present the crystal structure of Aspergillus flavus Rab7 (AflRab7), which reveals a well-ordered GTPase core, whereas its C-terminal tail is conserved across Aspergillus species yet lacks interpretable electron density, consistent with an intrinsically disordered region (IDR). Biochemical assays show that deletion of this IDR does not alter basal GTP hydrolysis, whereas genetic and cell-biological studies demonstrate that deletion of residues 191-205 causes severe growth retardation, defective conidiation and sclerotium formation, markedly reduces aflatoxin production, and fragmented vacuolar compartments. The IDR-deficient mutants further exhibit pronounced hypersensitivity to cell-wall stress and altered tolerance to membrane, osmotic, and redox challenges. Transcriptome profiling, supported by qPCR validation, reveals extensive transcriptional reprogramming upon loss of the C-terminal region, including dysregulation of pathways linked to development and secondary metabolism. Overall, our findings extend the mechanistic understanding of Rab7 beyond its catalytic pocket and establish the AflRab7 C-terminal IDR as a critical regulatory element that couples vacuolar dynamics to A. flavus development and aflatoxin biosynthesis, highlighting a tractable target for mitigating fungal toxigenic potential.