Post‐Translational Control of <scp>TaFT1</scp> by <scp>WAPO1</scp> Ubiquitination Shapes Spike Architecture and Yield in Wheat

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.