Stable mutation of Sucrose:Fructan 6-frucosyltransferase (6-SFT) in hexaploid wheat reduces grain fructan levels and leaf susceptibility to yellow rust

Fructans serve as key reserve carbohydrates in many grasses, including wheat, and are synthesised from sucrose through the coordinated action of the enzymes 6-SFT, 1-SST, and 1-FFT. Fructan polymers accumulate primarily in stem tissues and are later mobilised to support spike and grain development following anthesis. Previous work has suggested that fructans may function as host susceptibility factors, potentially enhancing the severity of Fusarium head blight (FHB). To investigate this, genome-edited (GE) 6-SFT knock-out lines were generated in the wheat cultivar Cadenza. Mutations consisting of 61–70 bp deletions were identified across the three homoeologous loci located on chromosomes 4AL, 7AS, and 7DS. These deletions resulted in frameshifts and premature stop codons. Phenotypic evaluation of T1–T3 triple homozygous lines under controlled environmental conditions showed that most edited lines were comparable to control plants in terms of growth, grain morphology, and yield components. Notably, one of the six lines produced a significantly increased thousand grain weight (TGW). Biochemical analyses revealed that fructan levels in grains of T1–T3 edited lines were significantly reduced relative to non-GE and wildtype Cadenza plants, while starch content remained consistent across T2 GE and control lines. A major focus of this study was the assessment of disease responses in the GE lines. T2 homozygous seedling inoculation assays revealed altered responses to biotrophic pathogens: five lines displayed moderate resistance to yellow rust, and one line showed moderate resistance to powdery mildew. Importantly, FHB phenotyping of T3 adult plant demonstrated that two independent lines consistently exhibited reduced disease severity, with lower infection levels observed between 7 and 14 days post-inoculation. These findings support the hypothesis that fructan metabolism can influence host–pathogen interactions. The 6-SFT knock-out lines therefore provide a valuable genetic resource for dissecting the role of carbohydrate partitioning in disease development and for breeding wheat varieties with improved resistance to multiple fungal pathogens.