Abstract：Expansin is a protein unique to the plant cell wall. It plays a key role in the expansion and relaxation of cell wall and decides the cell growth, to a great extent, during the process of plant growth. Both α-expansin (EXPA) and β-expansin (EXPB) are two larger expansin superfamilies. There are at least 34 α-expansin genes in rice (Oryza sativa). In this paper, we explored the effect of OsEXPA8 on cell division and growth of suspension cells from rice calli by transgenic techniques. Using the flow cytometry to analyze the difference of cell cycle between wild-type and transgenic suspension-cells for different culture time, we found that 35S::OsEXPA8 (overexpression) transgenic cells mainly remained in G2/M stage, while OsEXPA8-RNAi (knock-down) transgenic cells remain in G1 stage. Furthermore, the difference of cell number between wild-type and transgenic cells for different culture time were investigated by a hemocytometer, and the result showed 35S::OsEXPA8 overexpression cell＞wild-type cell＞OsEXPA8-RNAi transgenic cell number. In addition, the cell size was measured, and the result demonstrated 35S::OsEXPA8 overexpression cell＞wild-type cell＞OsEXPA8-RNAi transgenic cell. Finally, the callus was measured, and the result indicated 35S::OsEXPA8 overexpression callus＞wild-type callus＞OsEXPA8-RNAi transgenic callus. These results demonstrated that OsEXPA8 promoted suspension cell division and growth, and increased the cell number and size in rice. Therefore, OsEXPA8 plays an essential role in regulating the suspension cell growth and development in rice. This study would improve our understanding of the mechanism underlying the cell wall relaxation during plant cell growth, and can have signi?cant agricultural potential for improving crop growth by genetic modification.
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