Work

Deletion of Major Endoxylanase Genes in Fusarium graminearum Uncovers Distinct Virulence Phenotypes Influenced by the Genetic Background

Year: 2026

Type: article

Abstract: Fusarium graminearum, the main causal agent of Fusarium head blight of wheat, secretes endoxylanases to hydrolyse xylan, a major component of hemicellulose. Mutants of the highly expressed FGSG_03624 (xylB) gene previously showed a disease severity level similar to wild-type (WT) in wheat spikes. In this study, in contrast, three independent deletion mutants of FGSG_10999 (xylA), a second highly expressed endoxylanase gene, were significantly impaired in disease severity. Surprisingly, a knock-out mutant of xylA in the ΔxylB genetic background (ΔΔxylB+A) exhibited virulence comparable to that of ΔxylB and WT. The ΔxylA mutant shared with ΔΔxylB+A a marked reduction in xylanase activity during in vitro growth, and also with ΔxylB a decreased fungal biomass and deoxynivalenol (DON) accumulation in infected spikes. In contrast to ΔΔxylB+A and ΔxylB, ΔxylA revealed down-regulation of some endoxylanase and effector genes during spike infection. In addition, when grown on a wheat spike medium, the culture filtrate of ΔxylA showed a significant reduction in total protein secretion and a more severe impairment in necrotizing activity in Nicotiana benthamiana infiltrated leaves compared with ΔxylB and ΔΔxylB+A culture filtrates. When a deletion mutant of xylB was generated in the ΔxylA genetic background, the ΔΔxylA+B mutant displayed severely reduced virulence, similar to that of the parental ΔxylA. Altogether, these results demonstrate that xylA plays a critical role in F. graminearum pathogenicity through unexpected pleiotropic, network-level alterations, as also supported by the partial restoration observed by complementing the xylA gene in ΔxylA, highlighting the strong influence of genetic background on phenotypic outcomes.

Source: Molecular Plant Pathology

DOI: 10.1111/mpp.70362