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Summary: Argonaute (AGO) proteins and small RNAs (sRNAs) are core components of the RNA‐induced silencing complex (RISC). It has been reported that miRNAs regulate plant height and grain size in rice, but which AGO is involved in grain size regulation remains unclear. Here, we report that enhanced expression of OsAGO17, a putative AGO protein, could improve grain size and weight and promote stem development in rice. Cytological evidence showed that these effects are mainly caused by alteration of cell elongation. Expression analyses showed that OsAGO17 was highly expressed in young panicles and nodes, which was consistent with the expression pattern of OsmiR397b. SRNA sequencing, stem‐loop RT‐PCR and sRNA blotting showed that the expression of OsmiR397b was reduced in ago17 and enhanced in the OsAGO17 OE lines. Four OsmiR397b target laccase (LAC) genes showed complementary expression patterns with OsAGO17 and OsmiR397b. Combined with the results of immunoprecipitation (IP) analysis, we suggested that OsAGO17 formed an RISC with OsmiR397b and affected rice development by suppression of LAC expression. In conclusion, OsAGO17 might be a critical protein in the sRNA pathway and positively regulates grain size and weight in rice. [ABSTRACT FROM AUTHOR]

Background: Pollen development is an important reproductive process that directly affects pollen fertility and grain yield in rice. Argonaute (AGO) proteins, the core effectors of RNA-mediated silencing, play important roles in regulating plant growth and development. However, few AGO proteins in rice were reported to be involved in pollen development. In this study, artificial microRNA technology was used to assess the function of OsAGO17 in pollen development. Results: In this study, OsAGO17, a rice-specific gene, was specifically expressed in rice pollen grains, with the highest expression in uninucleate microspores. Downregulation of OsAGO17 by artificial microRNA technology based on the endogenous osa-miRNA319a precursor was successfully achieved. It is found that downregulation of OsAGO17 could significantly affect pollen fertility and cause pollen abortion, thus suggesting that OsAGO17 functions in rice pollen development. In addition, the downregulation of OsAGO17 mainly caused a low seed-setting rate, thereby resulting in the reduction of grain yield, whereas the downregulation of OsAGO17 did not significantly affect rice vegetative growth and other agricultural traits including number of florets per panicle, number of primary branch per panicle, and 100-grain weight. Furthermore, the result of subcellular localization analysis indicated that the OsAGO17 protein was localized to both the nucleus and the cytoplasm. Conclusion: These results represent the first report of the biological function for OsAGO17 in rice and indicate that OsAGO17 may possibly play crucial regulatory roles in rice pollen development. It helps us to better understand the mechanism of pollen development in rice. [ABSTRACT FROM AUTHOR]