Intragenic overexpression of TONNEAU 1b enhances grain length and weight in durum wheat

Grain yield is a complex trait determined by multiple genes, physiological and developmental processes, including those governed by cytoskeletal dynamics. In this study, we investigated the role of the TONNEAU 1b (TON1b) gene, a core component of the TON1–TRM–PP2A (TTP) complex involved in microtubule organization and cell division plane positioning, in the polyploid context of durum wheat (Triticum turgidum ssp. durum). To explore its function and agronomic potential, we developed intragenic Svevo lines overexpressing TON1b under the control of the endosperm-specific 1Dx5 promoter, using a CRE-LOX recombination system to produce marker-free genotypes. Molecular and phenotypic analyses of fixed intragenic lines revealed significant increases in grain length, grain weight, spikelet number and total starch content, without compromising grain number per spike. Transcriptomic profiling indicated consistent TON1b overexpression alongside downregulation of CEN1 and TON2, and upregulation of GW7, suggesting a regulatory role in both cell division and elongation processes. These findings suggest a role of TON1b on cytoskeletal remodelling and grain development, offering a promising genetic lever for yield improvement in durum wheat.