Post-Translational Control of TaFT1 by WAPO1 Ubiquitination Shapes Spike Architecture and Yield in Wheat

Abstract

The florigen protein TaFT1 coordinately regulates heading time and spikelet number per spike (SNS), serving as a key yield determinant in wheat. However, how its stability is post-translationally controlled in the shoot apical meristem remains unclear. Here, we identify the F-box protein WHEAT ORTHOLOG OF APO1 (WAPO1), allelic to a major SNS quantitative trait locus (QSns.cau-7A), as a direct ubiquitin E3 ligase targeting TaFT1 for degradation. A crucial missense mutation (C47F) in the F-box domain of WAPO1 has a significant impact on the SNS. The elite allele WAPO-A1b (from large-spike germplasm AS420, encoding 47F) exhibits stronger binding affinity and ubiquitination activity toward TaFT1 compared with the allele WAPO-A1f (from cultivar Lunxuan987, encoding 47C). Enhanced degradation of TaFT1 by WAPO-A1b in the shoot apical meristem impairs the TaFT1–TaFDL transcriptional complex, thereby downregulating the floral identity gene VRN1/WAP1 and increasing SNS without delaying heading. Notably, the favourable WAPO-A1b allele has been positively selected in modern breeding, and its ectopic activation significantly boosts grain yield in field trials. Our work elucidates a post-translational pathway that fine-tunes spike architecture and highlights WAPO-A1b as a valuable genetic target for high-yield wheat breeding.