TaFT‐D1 positively regulates grain weight by acting as a coactivator of TaFDL2 in wheat

Abstract

SummaryFLOWERING LOCUS T (FT), a multifunctional regulator in crops, modulates multiple key agronomic traits such as flowering time or heading date and plant height; however, its role in grain development regulation is unclear. Herein, through genome‐wide association studies (GWAS), we identified TaFT‐D1, which encodes a phosphatidylethanolamine‐binding protein (PEBP), as a candidate gene for grain weight in wheat. A one‐bp insertion/deletion (InDel) (G/‐) in the third exon of TaFT‐D1, resulting in different protein lengths, was significantly associated with grain weight. TaFT‐D1 knockout via the CRISPR‐Cas9 system reduced grain size and weight, and TaFT‐D1 increased grain size by promoting cell proliferation and starch synthesis. Transcriptome analysis revealed a significant decrease in the expression of cell cycle‐ and starch synthesis‐related genes, including TaNAC019‐3A, TaSWEET15‐like‐7B, TaCYCD4;1 and TaCYCD3;2, in the taft‐d1 knockout line. TaFT‐D1 interacted with the bZIP transcription factor TaFDL2, and the tafdl2 mutant presented relatively small grains, suggesting that TaFDL2 is a positive regulator of grain size. Moreover, TaFDL2 bound to the promoters of downstream cell cycle‐ and starch synthesis‐related genes, activating their expression, whereas TaFT‐D1 increased this activation via TaFDL2. Interaction assays demonstrated that TaFT‐D1, Ta14‐3‐3A and TaFDL2 formed a regulatory complex. Furthermore, the TaFT‐D1(G) allele was significantly correlated with greater thousand‐grain weight and earlier heading. This favourable allele has undergone strong positive selection during wheat breeding in China. Our findings provide novel insights into how TaFT‐D1 regulates grain weight and highlight its potential application for yield improvement in wheat.