). In this study, we obtain that TaCYP78A5 is hugely 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.eight and 9.six 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 number 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 rising grain weight and grain yield per plant and has been positively selected 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 inside the QTLs connected with grain PARP1 site thickness (GT), grain length (GL) and thousand-grain weight (TGW) in wheat (Figure S2). The above final results suggest that TaCYP78A5 might play an essential 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 building grains of wheat cultivar Shaan 512 which has large-size/heavy weight kernel (with TGW 52 g) by utilizing barley stripe mosaic virusinduced gene silencing (BSMV-VIGS) approach as reported previously (Ma et al., 2012). The result showed that the grain size and weight of TaCYP78A5-knockdown plants (BSMV: TaCYP78A5) were significantly lowered, compared with these on the handle plants (BSMV:00) (Figure S3a ). We additional investigated the cellular traits of seed coat, and located that the number of seed coat cells of BSMV:TaCYP78A5 plants was considerably decreased, however the size in the seed coat cell was not altered, compared with those with the control plants (Figure S3f ). These results recommend that TaCYP78A5 regulates grain weight by promoting proliferation of seed coat cells. To get elevated yield of transgenic wheat and further confirm the biological effect of TaCYP78A5, we generated transgenic wheat lines constitutively overexpressing TaCYP78A5-2A beneath the manage of maize ubiquitin promoter (named as UBI lines for simplicity). Nine independent transgenic SIRT2 site events have been obtained; of which two single-locus transgenic events (UBI-1 and UBI-4) with larger expression levels of TaCYP78A5 in comparison to wild-type plants (WT) are shown as representatives of UBI lines (Figure two). The grain length, width and thickness from the UBI lines increased by 9.three 0.3 , 9.four 0.0 and three.5 .0 , respectively, (Figure 2a ), which resulted in drastically increased grain weight (by 26.9 0.7 ), compared with that of WT (Figure 2d). Additional cytological evaluation of grains at 15 days after fertilization (DAF) indicated that both the quantity and the length of seed coat cells of UBI lines were considerably higher than these of WT (Figure 2e,f). Taken collectively, TaCYP78A5 includes a constructive role in growing grain weight of wheat. Un