The LARGE2-APO1/APO2 regulatory module controls panicle size and grain number in rice.

Panicle size and grain number are important agronomic traits and influence grain yield in rice (Oryza sativa), but the molecular and genetic mechanisms underlying panicle size and grain number control remain largely unknown in crops. Here we report that LARGE2 encodes a HECT-domain E3 ubiquitin ligase OsUPL2 and regulates panicle size and grain number in rice. The loss of function large2 mutants produce large panicles with increased grain number, wide grains and leaves, and thick culms. LARGE2 regulates panicle size and grain number by repressing meristematic activity. LARGE2 is highly expressed in young panicles and grains. Biochemical analyses show that LARGE2 physically associates with ABERRANT PANICLE ORGANIZATION1 (APO1) and APO2, two positive regulators of panicle size and grain number, and modulates their stabilities. Genetic analyses support that LARGE2 functions with APO1 and APO2 in a common pathway to regulate panicle size and grain number. These findings reveal a novel genetic and molecular mechanism of the LARGE2-APO1/APO2 module-mediated control of panicle size and grain number in rice, suggesting that this module is a promising target for improving panicle size and grain number in crops.

Natural Variation in the Promoter of GSE5 Contributes to Grain Size Diversity in Rice.

The utilization of natural genetic variation greatly contributes to improvement of important agronomic traits in crops. Understanding the genetic basis for natural variation of grain size can help breeders develop high-yield rice varieties. In this study, we identify a previously unrecognized gene, named GSE5, in the qSW5/GW5 locus controlling rice grain size by combining the genome-wide association study with functional analyses. GSE5 encodes a plasma membrane-associated protein with IQ domains, which interacts with the rice calmodulin protein, OsCaM1-1. We found that loss of GSE5 function caused wide and heavy grains, while overexpression of GSE5 resulted in narrow grains. We showed that GSE5 regulates grain size predominantly by influencing cell proliferation in spikelet hulls. Three major haplotypes of GSE5 (GSE5, GSE5DEL1+IN1, and GSE5DEL2) in cultivated rice were identified based on the deletion/insertion type in its promoter region. We demonstrated that a 950-bp deletion (DEL1) in indica varieties carrying the GSE5DEL1+IN1 haplotype and a 1212-bp deletion (DEL2) in japonica varieties carrying the GSE5DEL2 haplotype associated with decreased expression of GSE5, resulting in wide grains. Further analyses indicate that wild rice accessions contain all three haplotypes of GSE5, suggesting that the GSE5 haplotypes present in cultivated rice are likely to have originated from different wild rice accessions during rice domestication. Taken together, our results indicate that the previously unrecognized GSE5 gene in the qSW5/GW5 locus, which is widely utilized by rice breeders, controls grain size, and reveal that natural variation in the promoter region of GSE5 contributes to grain size diversity in rice.

SMALL GRAIN 11 Controls Grain Size, Grain Number and Grain Yield in Rice.

BACKGROUND: Grain size is one of key agronomic traits that determine grain yield in rice. Several regulators of grain size have been identified in rice, but the mechanisms that determine grain size and yield remain largely unknown. RESULTS: Here we characterize a small grain (smg11) mutant in rice, which exhibits small grains, dense panicles and the increased number of grains per panicle. Cloning and sequence analyses of the SMG11 gene reveal that smg11 is a new allele of DWARF2 (D2), which encodes a cytochrome P450 (CYP90D2) involved in brassinosteroid biosynthetic pathway. Overexpression of D2/SMG11 increases grain size and grain weight of wild-type plants. Overexpression of D2/SMG11 at a suitable level also significantly increases grain yield in rice. Cellular analyses indicate that D2/SMG11 controls grain size by promoting cell expansion. Further results reveal that D2/SMG11 influences expression of several known grain size genes involved in the regulation of cell expansion, revealing a novel link between D2/SMG11 and known grain size genes. CONCLUSIONS: SMG11 controls grain size by promoting cell expansion in grain hulls. SMG11 regulates cell expansion, at least in part, by influencing expression of several grain size genes involved in the regulation of cell expansion. The smg11 is a new allele of DWARF2/D2. The suitable expression of SMG11 increases grain size, grain weight and grain yield. Our findings reveal the functions of D2/SMG11 in grain size and grain yield, suggesting that the suitable expression of D2/SMG11 is a promising approach to improve grain yield in rice.