Work

Comprehensive functional mapping of accessory chromosomes identifies a dominant virulence-regulator paralog in tomato wilt pathogen

Year: 2026

Type: preprint

Abstract: Accessory chromosomes (ACs) serve as flexible genomic compartments that facilitate rapid adaptive evolution in eukaryotic microbes. In the tomato wilt pathogen Fusarium oxysporum f. sp. lycopersici , ACs are essential for virulence and host specificity; however, their structural complexity and functional redundancy have hindered a systematic characterization of their distinct roles. Here, we established a CRISPR/Cas9-based chromosomal dissection platform to generate a comprehensive functional map of pathogenicity determinants within ACs. Using this platform, we successfully generated a library of 36 large deletion mutants across the approximately 10 Mb putative AC region, enabling a chromosome-scale functional characterization of these compartments. A systematic screen of this library identified seven discrete AC segments that are indispensable for full virulence toward tomato. High-resolution chromosomal dissection of one virulence-associated segment through iterative subdivision and targeted gene disruption revealed that FTF1a-1 , a single member of the Fusarium transcription factor 1 ( FTF1 ) family that originated from the duplication of core-chromosomal virulence gene FTF2 into the AC region, functions as a dominant regulator of virulence. Given that the FTF1a-3 paralog contributes only marginally to virulence and the deletion of other paralogs does not markedly affect disease development, our findings demonstrate a functional hierarchy within the duplicated FTF1 gene family. These results imply that neofunctionalization of virulence genes within plastic fungal genomes promotes hyper-virulence and drives host-specific adaptation in F. oxysporum .

Source: bioRxiv (Cold Spring Harbor Laboratory)

DOI: 10.64898/2026.09.08.750270