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The grain number per panicle (GNP) is an important yield component. Identifying naturally favorable variations in GNP will benefit high-yield rice breeding. Here, we performed a genome-wide association study using a mini-core collection of 266 cultivated rice accessions with deep sequencing data and investigated the phenotype for three years. Three genes, i.e., TOTOU1 (TUT1), Grain height date 7 (Ghd7), and Days to heading 7/Grain height date 7.1/Pseudo-Response Regulator37 (DTH7/Ghd7.1/OsPRR37), which regulate GNP, were found in the quantitative trait loci (QTL) identified in this study. A stable QTL, qGNP1.3, which showed a strong correlation with variations in GNP, was repeatedly detected. After functional and transgenic phenotype analysis, we identified a novel gene, regulator of grain number 1a (RGN1a), which codes for protein kinase, controlling GNP in rice. The RGN1a mutation caused 37.2%, 27.8%, 51.2%, and 25.5% decreases in grain number, primary branch number per panicle, secondary branch number per panicle, and panicle length, respectively. Furthermore, breeding utilization analysis revealed that the additive effects of the dominant allelic variants of RGN1a and DTH7 played a significant role in increasing the grain number per panicle in japonica rice. Our findings enrich the gene pool and provide an effective strategy for the genetic improvement of grain numbers.

Drought is a major factor restricting the production of rice (Oryza sativa L.). The identification of natural variants for drought stress-related genes is an important step toward developing genetically improved rice varieties. Here, we characterized a member of the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) family, OsSPL10, as a transcription factor involved in the regulation of drought tolerance in rice. OsSPL10 appears to play a vital role in drought tolerance by controlling ROS production and stomatal movements. Haplotype and allele frequency analyses of OsSPL10 indicated that most upland rice and improved lowland rice varieties harbor the OsSPL10

Summary Yield in rice is determined mainly by panicle architecture. Using map‐based cloning, we identified an R2R3 MYB transcription factor REGULATOR OF GRAIN NUMBER1 (RGN1) affecting grain number and panicle architecture. Mutation of RGN1 caused an absence of lateral grains on secondary branches. We demonstrated that RGN1 controls lateral grain formation by regulation of LONELY GUY (LOG) expression, thus controlling grain number and shaping panicle architecture. A novel favourable allele, RGN1 C, derived from the Or‐I group in wild rice affected panicle architecture by means longer panicles. Identification of RGN1 provides a theoretical basis for understanding the molecular mechanism of lateral grain formation in rice; RGN1 will be an important gene resource for molecular breeding for higher yield.

The yield of rice is mostly affected by three factors, namely, panicle number, grain number and grain weight. Variation in panicle and grain numbers is mainly caused by tiller and panicle branches generated from axillary meristems (AMs). MOC1 encodes a putative GRAS family nuclear protein that regulates AM formation. Although several alleles of MOC1 have been identified, its variation in germplasm resources remains unclear. In the present study we characterized a novel moc1 allele named gnp6 which has a thymine insertion in the coding sequence of the SAW motif in the GRAS domain. This mutation causes arrested branch formation. The SAW motif is necessary for nuclear localization of GNP6/MOC1 where it functions as a transcription factor or co-regulator. Haplotype analysis showed that the coding region of GNP6/MOC1 was conserved without any non-synonymous mutations in 240 rice accessions. However, variation in the promoter region might affect the expression of it and its downstream genes. Joint haplotype analysis of GNP6/MOC1 and MOC3 showed that haplotype combinations H9, H10 and H11, namely MOC1-Hap1 in combination with MOC3-Hap3, MOC3-Hap4 or MOC3-Hap5 could be bred to promote branch formation. These findings will enrich the genetic resources available for rice breeders.

Heading date is a crucial agronomic trait. However, rice usually delays heading due to the photoperiod, temperature, hormones or age. The present research was conducted to analyze the mechanism controlling heading date in F1 hybrid rice. We constructed two test-crossing populations using two introgression lines (ILs), P20 and P21 coming from SH527/FH838 as the male parent, respectively, and male sterile line Jin23A as the female parent. Meanwhile, the F1 hybrids of H20, obtained by mating P20 with Jin23A and having no heading, and H21, from the crossing between P21 and Jin23A having normal heading, were both observed under long days. Here, we analyzed the photoperiodic response of F1 hybrids by transcriptome and metabolome profiling. The greater differences displayed in the transcriptome and the metabolome were caused by photoperiod (exogenous) instead of genes (endogenous). The coping mechanism resulted from long days (LD) in H20, leading to differences in the circadian rhythm and glutathione metabolism relative to other samples. The circadian oscillator and GSH/GSSG cycle typically regulate ROS homeostasis, and both of them are responsible for modulating ROS in H20 under LD condition. Both circadian rhythm genes and the reported genes related to heading date function via the DHD1/OsMFT1-Ehd1-RFT1-OsMADS14/OsMADS18 pathway and the glutathione metabolism pathway by regulating oxidative reduction processes. Both pathways are involved in the heading process and they interacted through the oxidative reduction process which was induced by photoperiod regulation, and all of them collectively modulated the heading process. The results of this study will be helpful for unraveling the mechanism of F1 hybrid responses to unheading under LD condition.

Panicle number (PN) is one of the three yield components in rice. As one of the most unstable traits, the dynamic change in tiller number (DCTN) may determine the final PN. However, the genetic basis of DCTN and its relationship with PN remain unclear. Here, 377 deeply re-sequenced rice accessions were used to perform genome-wide association studies (GWAS) for tiller/PN. It was found that the DCTN pattern rather than maximum tiller number or effective tiller ratio is the determinant factor of high PN. The DCTN pattern that affords more panicles exhibits a period of stable tillering peak between 30 and 45 days after transplant (called DT30 and DT45, respectively), which was believed as an ideal pattern contributing to the steady transition from tiller development to panicle development (ST-TtP). Consistently, quantitative trait loci (QTL) expressed near DT30-DT45 were especially critical to the rice DCTN and in supporting the ST-TtP. The spatio-temporal expression analysis showed that the expression pattern of keeping relatively high expression in root at 24:00 (R24-P2) from about DT30 to DT45 is a typical expression pattern of cloned tiller genes, and the candidate genes with R24-P2 can facilitate the prediction of PN. Moreover, gene OsSAUR27 was identified by an integrated approach combining GWAS, bi-parental QTL mapping and transcription. These findings related to the genetic basis underlying the DCTN will provide the genetic theory in making appropriate decisions on field management, and in developing new varieties with high PN and ideal dynamic plant architecture.

MoHrip2 Magnaporthe oryzae hypersensitive protein 2 is an elicitor protein of rice blast fungus M. oryzae. Rice seedlings treated with MoHrip2 have shown an induced resistance to rice blast. To elucidate the mechanism underlying this MoHrip2 elicitation in rice, we used differential-display 2-D gel electrophoresis and qRT-PCR to assess the differential expression among the total proteins extracted from rice leaves at 24 h after treatment with MoHrip2 and buffer as a control. Among ~1000 protein spots detected on each gel, 10 proteins were newly induced, 4 were up-regulated, and 3 were down-regulated in MoHrip2-treated samples compared with the buffer control. Seventeen differentially expressed proteins were detected using MS/MS analysis and categorized into six groups according to their putative function: defense-related transcriptional factors, signal transduction-related proteins, reactive oxygen species (ROS) production, programmed cell death (PCD), defense-related proteins, and photosynthesis and energy-related proteins. The qPCR results (relative expression level of genes) further supported the differential expression of proteins in MoHrip2-treated rice leaves identified with 2D-gel, suggesting that MoHrip2 triggers an early defense response in rice leaves via stress-related pathways, and the results provide evidence for elicitor-induced resistance at the protein level.