Objective RAC/ROPs are a class of plant-specific small G proteins, which are involved in multiple signaling pathways as molecular switches. OsRAC3 regulates rice (Oryza sativa L.) crown root development by interacting with cytokinin signaling components. However whether it affects traits in the aboveground parts of rice remains unclear. This study mainly aims to analyze the effects of OsRAC3 on spike development and yield traits of rice.

Method The inflorescence tissue of rice OsRAC3promoter::GUS transgenic plants were stained with GUS to analyze the expression pattern of OsRAC3. We also analyzed the main agronomic traits such as number of grains per spike, grain length, grain width and thousand grain weight of two experimental materials, constitutively activated mutant (CA-osrac3) and dominant negative mutant (DN-osrac3).

Result OsRAC3 was strongly expressed in floral meristems, stamen and pistill. CA-osrac3 had fewer grains but its grain length, grain width and thousand grain weight were significantly higher than those of wild-type. DN-osrac3 had a low number of spike branches and poor fertility, while the grain length, grain width and thousand grain weight were significantly lower than those of wild-type.

Conclusion OsRAC3 affects the developmental process of rice spikes, and the constitutively activated mutant CA-osrac3 promotes the growth of rice seeds. OsRAC3 has important applications in high-yield breeding and genetic improvement of rice.