Wheat, Triticum aestivum, is one of the world’s major cereal crops and is of considerable importance to human nutrition, supplying one-fifth of the calories consumed by humans. For important food crops such as wheat, rice and maize, grain yield mainly depends on grain number and size. In rice (Oryza sativa), GW2 was isolated from a major quantitative trait locus for grain size and weight, and encodes an E3 RING ligase that negatively regulates these yield components. Wheat has TaGW2 homologs in A, B and D genomes; and copies show distinct expression pattern during whole grain development in wheat. TaGW2-A was mapped in a genomic region on 6AS, encompassing previous reported QTLs for yield; and polymorphisms in TaGW2-A (promoter and intron 7) were associated with thousand-grain weight, in a worldwide wheat core collection. To investigate TaGW2 function, RNA interference was used to down-regulate TaGW2 transcripts levels. Surprisingly, transgenic wheat lines significantly showed decreased grain weight and size-related dimensions, and endosperm cell number compared to controls. The present study thus suggests that TaGW2 is a positive regulator of the final grain size in wheat, conversely to GW2 in rice. Biochemical and molecular analyses of the protein TaGW2-A revealed that 1) TaGW2-A is a functional E3 ubiquitine ligase in vitro, 2) TaGW2-A accumulates in the nucleolus, the nucleoplasm, and the cytosol, 3) E3 ubiquitine ligase activity seems to impact TaGW2-A subcellular localization. To investigate the TaGW2 signalling pathway(s), cDNA library from whole wheat grains was built and screened with the bait protein TaGW2(1-320). Preliminary results from the interactomic study suggest that TaGW2 may regulate cell division. Moreover, TaGW2 may also function as an E3 Nedd8 ligase, besides its E3 ubiquitin ligase function.
