SummaryGrain weight is the most important component of rice yield and is mainly determined by grain size, which is generally controlled by quantitative trait loci (QTLs). Although numerous QTLs that regulate grain weight have been identified, the genetic network that controls grain size remains unclear. Herein, we report the cloning and functional analysis of a dominant QTL, grain length and width 2 (GLW2), which positively regulates grain weight by simultaneously increasing grain length and width. The GLW2 locus encodes OsGRF4 (growth‐regulating factor 4) and is regulated by the microRNA miR396c in vivo. The mutation in OsGRF4 perturbs the OsmiR396 target regulation of OsGRF4, generating a larger grain size and enhanced grain yield. We also demonstrate that OsGIF1 (GRF‐interacting factors 1) directly interacts with OsGRF4, and increasing its expression improves grain size. Our results suggest that the miR396c‐OsGRF4‐OsGIF1 regulatory module plays an important role in grain size determination and holds implications for rice yield improvement.

Leaves, the collective organ produced by the shoot apical meristem (SAM), are polarized along their adaxial-abaxial axis. In this study, we characterized two rice (Oryza sativa) allelic rolled-leaf mutants, rolled leaf 9-1 (rl9-1) and rl9-2, which display very similar phenotypes with completely adaxialized leaves and malformed spikelets. We cloned the RL9 gene by way of a map-based cloning strategy. Molecular studies have revealed that RL9 encodes a GARP protein, an orthologue of Arabidopsis KANADIs. RL9 is mainly expressed in roots, leaves, and flowers. The transient expression of a RL9-GFP (green fluorescent protein) fusion protein has indicated that RL9 protein is localized in the nucleus, suggesting that RL9 acts as a putative transcription factor.

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Higher yields of rice have always been a predominant goal in rice breeding techniques. However, the inheritances of rice yield and its components are still unknown, and no information regarding suitable alleles can be directly provided for improving the rice yield level until three major quantitative trait loci (QTLs) have been cloned and functionally characterized. These QTLs contain Gn1a for grain number per panicle and GS3 and GW2 for grain weight. It has been proven that these three genes show a potential in improving the rice yield level. However, the distribution of suitable alleles on these three loci in rice cultivars and germ plasm are yet to be elucidated, this retards the progress of the utilization of suitable alleles in rice breeding techniques to produce higher yields. In the present study, we developed a set of gene-tagged markers based on the gene mutation sites Gn1a-M1 and Gn1a-M2 for Gn1a, GW2-HapI for GW2, and GS3-PstI for GS3. The results demonstrated that these STS markers could clearly differentiate between the different alleles at each gene locus. A survey of the allele distributions of the abovementioned three genes was performed with 156 cultivars. It was observed that the 5150-Gn1a allele was absent on the Gn1a locus and only two type alleles (Ha-Gn1a and Ko-Gn1a) were present, of which 54.3% indica and 21.5% japonica cultivars contained the Ha-Gn1a allele. Two alleles (MH-GS3 and ZS-GS3) were detected on the GS3 locus, and 48.6% indica and 9.9% japonica cultivars harbored the suitable allele MH-GS3. Further, all the cultivars contained the FA-GW2 allele on GW2, whereas the WY-GW2 allele was not found. These results further suggested that some of the alleles residing in the indica subspecies have introgressed into the japonica group with a very low frequency. The gene-tagged markers developed in the present study can be directly used as a tool for marker-aided selection (MAS) in rice breeding techniques to produce higher yields.