Overexpression of the 16‐ kD a α‐amylase/trypsin inhibitor RAG 2 improves grain yield and quality of rice

Summary Increasing grain yield and improving grain quality are two important goals for rice breeding. A better understanding of the factors that contribute to the overall grain quantity and nutritional quality of rice will lay the foundation for developing new breeding strategies. RAG 2 is a member of 14‐to‐16‐ kD a α‐amylase/trypsin inhibitors in rice, which belong to the albumin of seed storage proteins. We found that RAG 2 was specifically expressed in ripening seed and its transcription peak was between 14 and 21 days after flowering. Grain size and 1000‐grain weight were obviously increased in RAG 2 ‐overexpressed lines compared with wild type, and grain size was reduced in RAG 2 ‐suppressed lines. In addition, the major storage substances of the seeds differed significantly in RAG 2 ‐overexpressed and RAG 2 ‐suppressed lines compared to wild type. The protein content and amount of total lipids were increased and decreased, respectively, in the seeds of RAG 2 ‐overexpressed and RAG 2 ‐suppressed lines. Overexpression of RAG 2 significantly increased grain size and improved grain quality and yield simultaneously. These results imply that RAG 2 might play an important role in regulating grain weight and seed quality of rice. The functional characterization of rice RAG 2 facilitates a further understanding of the mechanisms involved in grain size and seed quality and may be helpful in improving grain yield and quantity in cereal crops.