AUTHOR=Vlieger Babette V. , Fokkens Like , Takken Frank L. W. , Rep Martijn 

TITLE=Divergent ECC1 effector homologs modulate host-specific virulence in cucurbit-infecting Fusarium oxysporum

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=Volume 15 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2025.1656785

DOI=10.3389/fcimb.2025.1656785

ISSN=2235-2988

ABSTRACT=Fusarium oxysporum (Fo) is a soil-borne fungal pathogen that causes wilt disease in
over one hundred plant species, with host-specific strains classified into formae
speciales (ff. spp.). For example, Fo f. sp. melonis (Fom) only causes
disease in melon while Fo f. sp. radicis-cucumerinum (Forc) can infect multiple
cucurbit species. The virulence factors underlying host specificity in these cucurbit-infecting formae  speciales have largely remained elusive, limiting our understanding of Fo-host interactions. A previous study identified Effector for Cucurbit Compatibility 1a (ECC1a), an avirulence protein from Fom that restricts cucumber infection when introduced into Forc. Here, we show that ECC1a is part of a previously unrecognized effector gene family, ECC1, abundantly present in strains that infect one or more cucurbit species. However, the role of this family in host compatibility is still poorly understood. Using gene knockout- and replacement strategies, we show that the ECC1 gene family contributes to virulence of both Forc and Fom on cucumber and melon. Specifically, ECC1a contributes to Fom virulence on melon and Forc virulence on cucumber. ECC1b appears to be primarily involved in Fom virulence on melon.Expression profiling reveals a potential role of ECC1 during early stages of infection, suggesting involvement in initial host colonization. Together, these findings highlight the host- and forma specialis-specific functions of ECC1 homologs in Fo pathogenicity.