RING finger E3 ligases play an important role in regulating plant growth and development by mediating substrate degradation. In this study, we identified TaGW2L, encoding a Grain width and weight2 (GW2)-like RING finger E3 ligase, as a novel positive regulator of heading date in wheat (Triticum aestivum L.). TaGW2L exhibited high amino acid sequence similarities with TaGW2 homoeologs, particularly in the conserved RING finger domain. Expression analysis indicated that TaGW2L was constitutively expressed in various wheat tissues. TaGW2L showed transactivation activity in yeast and could interact with the ubiquitin-conjugating enzymes E2s. An in vitro ubiquitination assay verified that TaGW2L possessed a similar E3 ligase activity to TaGW2. Overexpression of the TaGW2L-7A homoeolog in wheat led to a significantly earlier heading date under both natural conditions and long-day conditions. Transcriptome analysis revealed that multiple known genes positively regulating wheat heading were significantly upregulated in the TaGW2L-7A-overexpression plants compared with the wild-type control. Together, our findings shed light on the role of TaGW2L in wheat heading date and provide potential applications of TaGW2L for the adaptation improvement of crops.

Grain Weight 8 (GW8) in rice is a SQUAMOSA Promoter-Binding Protein-Like (SPL) family transcription factor with multiple biological functions. In this study, three GW8 homoeologs were cloned from homoeologous group 7 chromosomes of wheat. Subcellular localization and trans-activation activity assays suggested that TaGW8 is a transcriptional activator. TaGW8 genes were preferentially expressed in young spikes and developing grains. Ectopic expressions of TaGW8 in Arabidopsis and rice resulted in enhanced vegetative growth, earlier flowering and larger seeds. TaGW8-7A was the most highly variable of the three homoeologs with four haplotypes (Hap-1/2/3/4). TaGW8-7B had two haplotypes (Hap-L/H). TaGW8-7A-Hap-2 was associated with high thousand-grain weight (TGW) and large kernel length and showed higher transcriptional levels and binding activity than the other haplotypes. The high frequency of TaGW8-7A-Hap-2 in Chinese wheat populations suggested that it had been extensively selected in breeding. This haplotype showed a high potential for exploitation in global wheat breeding because its frequency was low in exotic germplasm. TaGW8-7B-Hap-H produced abundant transcripts and was associated with early heading and maturity, less tiller number and high TGW. This haplotype might be suitable for multiple cropping systems due to short wheat season. In this study we identified sub-functionalization among TaGW8 homoeologs and obtained functional molecular markers that can be used in breeding for high grain yield.