Expression of a rice OsARGOS gene in Arabidopsis promotes cell division and expansion and increases organ size.

The ARGOS gene in Arabidopsis plays a key role in controlling plant organ size. To determine the function of it's ortholog in rice, a putative ARGOS orthologous gene from rice tissues was isolated and designated as OsARGOS. This gene has only one copy in the rice genome. OsARGOS transcripts were detected in most of rice tissues, particularly in the young tissues, and its expression was induced in rice seedlings by the application of either auxin or cytokinin. Arabidopsis plants expressing OsARGOS led to larger organs, such as leaves and siliques, compared with wild-type plants. Interestingly, the root growth was also enhanced in these transgenic Arabidopsis plants. Therefore, the biomass of the transgenic plants was significantly increased. Further analysis revealed that, different from the ARGOS and ARGOS-LIKE genes in Arabidopsis, the OsARGOS gene enlarged organ by an increase in both cell number and cell size. In addition, the transcript levels of several organ size-associated genes regulating either cell division or cell growth were upregulated in the transgenic Arabidopsis plants. We also transferred the OsARGOS gene to rice, but the transgenic plants did not show any changes in organ size compared with the control plants. It is likely that the function of OsARGOS in organ size control depends on other size regulators in rice. The expression of OsARGOS in Arabidopsis may activate the signaling pathways that control cell proliferation and cell expansion during the course of plant growth and development. Since the expression of OsARGOS causes organ enlargement, the potential application of this gene through genetic engineering may significantly improve the production of biomass in agricultural practice.