Grain yield in many cereal crops is largely determined by grain size. Here we report the genetic and molecular characterization of GS3, a major quantitative trait locus for grain size. It functions as a negative regulator of grain size and organ size. The wild-type isoform is composed of four putative domains: a plant-specific organ size regulation (OSR) domain in the N terminus, a transmembrane domain, a tumor necrosis factor receptor/nerve growth factor receptor (TNFR/NGFR) family cysteine-rich domain, and a von Willebrand factor type C (VWFC) in the C terminus. These domains function differentially in grain size regulation. The OSR domain is both necessary and sufficient for functioning as a negative regulator. The wild-type allele corresponds to medium grain. Loss of function of OSR results in long grain. The C-terminal TNFR/NGFR and VWFC domains show an inhibitory effect on the OSR function; loss-offunction mutations of these domains produced very short grain. This study linked the functional domains of the GS3 protein to natural variation of grain size in rice.grain weight | Oryza sativa L. | protein domain | yield I n recent years, genes for grain and fruit sizes have been isolated from several plant species (1-8), providing opportunities for understanding genetic and molecular mechanisms regulating these traits. In rice, yield per plant is determined by three component traits: number of panicles (tillers) per plant, number of grains per panicle, and grain weight. Extensive genome mapping studies have identified hundreds of QTLs (quantitative trait loci) for yield traits (9). Although a number of QTLs for tillering (10), grain number (11, 12), grain size (8, 13-15), and panicle size and plant architecture (16-18) have been cloned, molecular characterization of these and many more genes is needed to understand the genetic and molecular bases of yield (9).A major QTL for grain size (GS3) in rice was previously identified on chromosome 3 in a number of studies across different genetic backgrounds and environments (19)(20)(21). Fan et al. (8) identified the candidate gene for GS3. By comparative sequencing analysis, they found a nonsense mutation in the second exon of the putative GS3 shared among all of the large-grain varieties tested in comparison with varieties with smaller grains. This mutation caused a 178-aa truncation in the C terminus of the predicted protein, which was widespread in the global rice germplasm collections (22, 23), indicating that this mutation had an ancient origin and played an important role in grain size variation and domestication of the cultivated rice.Here we report the genetic and molecular analysis of GS3, which revealed several important structural and functional features of the GS3 protein in grain size regulation. ResultsValidation of GS3 on Grain Size Regulation. We validated the effect of GS3 on grain size by transformation. A construct CT9.8 (Fig. S1A), containing a 9.8-kb genomic DNA fragment encompassing GS3 amplified by PCR from rice cultivar Chuan 7 (short grain)...

Manipulating grain size is an effective strategy for increasing cereal yields. Here we identify a pathway composed of five subunits of the heterotrimeric G proteins that regulate grain length in rice. The Gβ protein is essential for plant survival and growth. Gα provides a foundation for grain size expansion. Three Gγ proteins, DEP1, GGC2 and GS3, antagonistically regulate grain size. DEP1 and GGC2, individually or in combination, increase grain length when in complex with Gβ. GS3, having no effect on grain size by itself, reduces grain length by competitively interacting with Gβ. By combining different G-protein variants, we can decrease grain length by up to 35% or increase it by up to 19%, which leads to over 40% decreasing to 28% increasing of grain weight. The wide existence of such a conserved system among angiosperms suggests a possible general predictable approach to manipulating grain/organ sizes.

Grasses produce tiller and panicle branching at vegetative and reproductive stages; the branching patterns largely define the diversity of grasses and constitute a major determinant for grain yield of many cereals. Here we show that a spatiotemporally coordinated gene network consisting of the MicroRNA 156 (miR156/)miR529/ SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) and miR172/ APETALA2 (AP2) pathways regulates tiller and panicle branching in rice. SPL genes negatively control tillering, but positively regulate inflorescence meristem and spikelet transition. Underproduction or overproduction of SPLs reduces panicle branching, but by distinct mechanisms: miR156 and miR529 fine-tune the SPL levels for optimal panicle size. miR172 regulates spikelet transition by targeting AP2-like genes, which does not affect tillering, and the AP2-like proteins play the roles by interacting with TOPLESS-related proteins (TPRs). SPLs modulate panicle branching by directly regulating the miR172/ AP2 and PANICLE PHYTOMER2 (PAP2)/Rice TFL1/CEN homolog 1 (RCN1) pathways and also by integrating other regulators, most of which are not involved in tillering regulation. These findings may also have significant implications for understanding branching regulation of other grasses and for application in rice genetic improvement.he architecture of grasses is largely determined by the branching patterns. Tillers and inflorescence branches are produced at vegetative and reproductive stages, respectively, and their patterns greatly contribute to the diversity of grasses and constitute a major determinant of grain yield of major cereals.Rice branching has attracted much attention because of its importance in food production. Axillary buds produce tillers during the vegetative stage. However, only the early ones formed from the unelongated internodes outgrow as tillers, whereas later ones formed from the upper internodes remain dormant. After reproductive transition, the shoot apical meristem is converted to inflorescence meristem to produce panicle. Rice panicle morphology is largely determined by the timing of identity transition among the different types of meristems (SI Appendix, Fig. S1). Therefore, fine-tuning of meristem phase change at reproductive stage defines the size and architecture of the rice panicle (1).Many genes have been identified as regulators of rice branching. Generally, genes involved in axillary bud initiation control both vegetative and reproductive branching, whereas genes under axillary bud outgrowth have specific roles only at certain stages (2, 3). LAX PANICLE 1 (LAX1) and MONOCULM1 control axillary bud initiation; mutation in either of them results in reduction of both tiller and panicle branches (4, 5). Other genes such as Grain number, plant height, and heading date7 exclusively control panicle branching (6). As a third class, many genes, including Ideal Plant Architecture 1 (IPA1)/Wealthy Farmer's Panicle (WFP) and genes related to strigolactone, play opposite roles in tiller and panicle branches (7-9). Therefore...

Grain protein content (GPC) affects rice nutrition quality. Here, we identify two stable quantitative trait loci (QTLs), qGPC-1 and qGPC-10 , controlling GPC in a mapping population derived from indica and japonica cultivars crossing. Map-based cloning reveals that OsGluA2 , encoding a glutelin type-A2 precursor, is the candidate gene underlying qGPC-10 . It functions as a positive regulator of GPC and has a pleiotropic effect on rice grain quality. One SNP located in OsGluA2 promoter region is associated with its transcript expression level and GPC diversity. Polymorphisms of this nucleotide can divide all haplotypes into low ( OsGluA2 LET ) and high ( OsGluA2 HET ) expression types. Population genetic and evolutionary analyses reveal that OsGluA2 LET , mainly present in japonica accessions, originates from wild rice. However, OsGluA2 HET , the dominant type in indica , is acquired through mutation of OsGluA2 LET . Our results shed light on the understanding of natural variations of GPC between indica and japonica subspecies.

Stigma exsertion, a key determinant of the rice mating system, greatly contributes to the application of heterosis in rice. Although a few quantitative trait loci associated with stigma exsertion have been fine mapped or cloned, the underlying genetic architecture remains unclear. We performed a genome-wide association study on stigma exsertion and related floral traits using 6.5 million SNPs characterized in 533 diverse accessions of Oryza sativa. We identified 23 genomic loci that are significantly associated with stigma exsertion and related traits, three of which are co-localized with three major grain size genes GS3, GW5, and GW2. Further analyses indicated that these three genes affected the stigma exsertion by controlling the size and shape of the spikelet and stigma. Combinations of GS3 and GW5 largely defined the levels of stigma exsertion and related traits. Selections of these two genes resulted in specific distributions of floral traits among subpopulations of O. sativa. The low stigma exsertion combination gw5GS3 existed in half of the cultivated rice varieties; therefore, introducing the GW5gs3 combination into male sterile lines is of high potential for improving the seed production of hybrid rice.

The use of alkaline salt lands for crop production is hindered by a scarcity of knowledge and breeding efforts for plant alkaline tolerance. Through genome association analysis of sorghum, a naturally high-alkaline–tolerant crop, we detected a major locus, Alkaline Tolerance 1 ( AT1 ), specifically related to alkaline-salinity sensitivity. An at1 allele with a carboxyl-terminal truncation increased sensitivity, whereas knockout of AT1 increased tolerance to alkalinity in sorghum, millet, rice, and maize. AT1 encodes an atypical G protein γ subunit that affects the phosphorylation of aquaporins to modulate the distribution of hydrogen peroxide (H 2 O 2 ) . These processes appear to protect plants against oxidative stress by alkali. Designing knockouts of AT1 homologs or selecting its natural nonfunctional alleles could improve crop productivity in sodic lands.

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