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.

Common wheat (Triticum aestivum L.) is one of the most important crops because it provides about 20% of the total calories for humans. T. aestivum is an excellent modern species for studying concerted evolution of sub-genomes in polyploid species, because of its large chromosome size and three well-known genome donors. Establishment of common wheat genome reference sequence and development of high-density SNP chips provide an excellent foundation to answer questions of wheat evolution and breeding at the genomic level. By genotyping more than 600 accessions of common wheat and their diploid and tetraploid ancestors using a Wheat660K SNP array, we found dramatic genome changes due to tetraploidization and hexaploidization, in contrast to weaker influences of domestication and breeding on them. Further, since common wheat was introduced in China in 1500 BCE, Chinese landraces formed two subgroups (T. aestivum-L1 and T. aestivum-L2) with considerably diverse geographic distributions and agronomic traits. T. aestivum-L2, mainly distributed in central and east China is found to have more but smaller oval grains with early maturity characteristics. We found that variation and selection in intergenic regions of the A and B sub-genomes dominated this differentiation, in which chromosomes 7A and 3B took the leading roles due to the existence of putative genes related to defense responses and environmental adaption in the highly differentiated regions. Large haplotype blocks were detected on 3B (232.6–398.3 Mb) and 7A (211.7–272.9 Mb) in the landraces, forming two distinct haplotypes, respectively. We discovered that artificial crosses in breeding promoted recombination in the whole genome, however, this recombination and differentiation was highly asymmetric among the three sub-genomes in homoeologous regions. In addition, we found that the wide use of European and northern American cultivars in breeding at early era, led dramatic changes in Chinese wheat genome, whereas, the recent breeding functioned to optimize it. This study will provide the insight for reconsideration of wheat evolution and breeding, and a new strategy for parent selection in breeding.

The TaGS3 homoeologous genes (homoeologs) located on chromosomes 7A, 4A, and 7D in hexaploid wheat were cloned. Relative expression analysis of the three TaGS3 homoeologs revealed that the expression levels of TaGS3-4A and TaGS3-7D in developing grains were higher than that of TaGS3-7A. Genetic evidence showed that TaGS3 was a negative regulator of grain weight and grain size. Fifteen polymorphic sites and five haplotypes were detected in TaGS3-4A. Two molecular markers were developed to distinguish the five haplotypes. Association analysis using 260 accessions from Chinese wheat mini-core collection (MCC) indicated that TaGS3-4A affected thousand grain weight (TGW) and grain length (GL). HAP-4A-1 and HAP-4A-2 were favorable haplotypes that increased TGW and GL and had undergone strong selection during domestication of wheat. In addition, interaction of the TaGS3-4A and TaGS3-7D homoeologs had significant additive effects on the grain traits. Hap-4A-1/Hap-7D-2 was the best haplotype combination in increasing TGW and GL. The frequencies and geographic distributions of favorable TaGS3 haplotypes among 1388 wheat accessions from worldwide sources provided clues for selection of yield-related traits. Our findings demonstrated that TaGS3-4A had significant effects on TGW and GL. Marker-assisted selection of HAP-4A-1/2 combined with HAP-7D-2 has potential to increase wheat yields.

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.