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

Yinhui Zhang, Haixia Liu, Yaojia Wang, Xuemei Si, Yuxue Pan, Mengjiao Guo, Meijuan Wu, Yuanhao Li, Hongxia Liu, Xueyong Zhang, Jian Hou, Tian Li, Chenyang Hao

Plant Biotechnology Journal; 18 March 2025; https://doi.org/10.1111/pbi.70032

Summary

FLOWERING 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.

See https://onlinelibrary.wiley.com/doi/10.1111/pbi.70032

Figure 1

FT-D1 was identified as a candidate gene controlling thousand-grain weight (TGW) on chromosome 7D through GWAS. (a) Manhattan and QQ plots showing significant associations with TGW on chromosome 7D for multiple environments. The black dashed line represents the threshold value. (b) Linkage disequilibrium diagram for peak SNPs. The black line at the top indicates the locations of candidate genes within this region, and the red star highlights the specific position of the candidate gene TaFT-D1. (c) Predicted expression profiles of 13 candidate genes in this region at different developmental phases and tissues according to an online public database (https://www.wheat-expression.com/). 1, roots, seedling (n = 8); 2, leaves/shoots, seedling (n = 174); 3, leaves/shoots, vegetative (n = 156); 4, roots, vegetative (n = 73); 5, leaves/shoots, reproductive (n = 151); 6, roots, reproductive (n = 8); 7, spike, reproductive (n = 278); 8, grain, reproductive (n = 166); and 9, spike, vegetative (n = 2). (d) Gene structure and key mutation sites of the candidate gene TaFT-D1. (e) Cloud and rain plot showing that FT-D1(G) has a significantly higher TGW BLUP value than does FT-D1(−). A natural population (NP) of 145 landmark cultivars were classified on the basis of a single nucleotide (G) insertion and deletion (InDel) in TaFT-D1. The scatter points represent these cultivars.