A Role of Cytochrome P450 Protein CYP78As in the Control of Seed Size in Wheat (Triticum aestivum L.)

There are several studies describing quantitative trait loci (QTL) for seed size in wheat, but the relevant genes and molecular mechanisms remain largely unknown. Here, we report the functional characterization of the wheat TaCYP78A3 gene and its effect on seed size. TaCYP78A3 encoded wheat cytochrome P450 CYP78A3 and was specifically expressed in wheat reproductive organs. TaCYP78A3 activity was positively correlated with the final seed size. Its silencing caused cell number reduction in the seed coat, resulting in a 11% decrease in wheat seed size, whereas TaCYP78A3 overexpression induced more cells in the seed coat, leading to a 11%~48% increase in Arabidopsis seed size. In addition, the cell number of the final seed coat was determined by the TaCYP78A3 expression level, which affected the extent of integument cell proliferation in the developing ovule and seed. Unfortunately, TaCYP78A3 overexpression caused a reduced seed set due to an ovule developmental defect in Arabidopsis. Moreover, TaCYP78A3 overexpression affected embryo development by promoting embryo integument cell proliferation during seed development, which also ultimately affected the final seed size in Arabidopsis. In summary, our results indicated that TaCYP78A3 plays critical roles in influencing seed size by affecting the extent of integument cell proliferation. The present study provides direct evidence that TaCYP78A3 functions in affecting seed size in wheat and contributes to an understanding of the cellular basis of the gene influencing seed development.