). In this study, we obtain that TaCYP78A5 is highly expressed in ovaries and seed coat and locates inside the QTLs for grain weight and yield-related traits in wheat. Modified expression of TaCYP78A5 in maternal integument enhances grain weight and grain yield per plant by 4.3 8.8 and 9.6 4.7 , respectively, in field trials. Transcriptome and hormone metabolome analyses reveal that TaCYP78A5 participates in auxin synthesis pathway and promotes auxin accumulation and cell wall remodelling in ovary. Phenotype investigation and cytological observation show that localized overexpression of TaCYP78A5 in ovary outcomes in delayed flowering, which prolongs proliferation of maternal integument cells, increases the amount of seed coat cell and sooner or later promotes grain enlargement. Association analysis demonstrates that TaCYP78A5 haplotype Ap-HapII with greater activity is favourable for growing grain weight and grain yield per plant and has been positively chosen in wheat breeding in China. These findings reveal that TaCYP78A5 can serve as a valuable gene for enhancing wheat yield. recognized genetic maps, physical map and wheat genome reference sequence IWGSC Ref v1.0 (IWGSC, 2018). The outcomes showed that TaCYP78A5-2A locates within the QTLs related with grain thickness (GT), grain length (GL) and thousand-grain weight (TGW) in wheat (Figure S2). The above final results recommend that TaCYP78A5 may possibly play an important role in regulating grain weight and yield.Constitutive overexpression of TaCYP78A5 enhances grain weight but not grain yield per plantTo verify if TaCYP78A5 affects grain weight of wheat, we knocked down the expression of TaCYP78A5 in developing grains of wheat cultivar Shaan 512 which has large-size/heavy weight kernel (with TGW 52 g) by using barley stripe mosaic virusinduced gene silencing (BSMV-VIGS) technique as reported previously (Ma et al., 2012). The outcome showed that the grain size and weight of TaCYP78A5-knockdown plants (BSMV: TaCYP78A5) were significantly reduced, mGluR4 list compared with those from the control plants (BSMV:00) (Figure S3a ). We further investigated the cellular characteristics of seed coat, and identified that the amount of seed coat cells of BSMV:TaCYP78A5 plants was considerably decreased, but the size in the seed coat cell was not altered, compared with those of the control plants (Figure S3f ). These final results suggest that TaCYP78A5 regulates grain weight by promoting proliferation of seed coat cells. To receive enhanced yield of transgenic wheat and further confirm the biological impact of TaCYP78A5, we generated transgenic wheat lines constitutively overexpressing TaCYP78A5-2A below the handle of maize ubiquitin promoter (named as UBI lines for simplicity). Nine independent transgenic events had been obtained; of which two single-locus transgenic events (UBI-1 and UBI-4) with larger expression levels of TaCYP78A5 compared to Nav1.1 site wild-type plants (WT) are shown as representatives of UBI lines (Figure 2). The grain length, width and thickness from the UBI lines increased by 9.3 0.3 , 9.4 0.0 and three.5 .0 , respectively, (Figure 2a ), which resulted in substantially enhanced grain weight (by 26.9 0.7 ), compared with that of WT (Figure 2d). Additional cytological evaluation of grains at 15 days following fertilization (DAF) indicated that both the quantity along with the length of seed coat cells of UBI lines have been considerably larger than these of WT (Figure 2e,f). Taken collectively, TaCYP78A5 features a optimistic part in increasing grain weight of wheat. Un