Activation of Big Grain1 significantly improves grain size by regulating auxin transport in rice

Temporal Gene Expression Profiles From Pollination to Seed Maturity in Sorghum Provide Core Candidates for Engineering Seed Traits

Sorghum (Sorghum bicolor (L.) Moench) is a highly nutritional multipurpose millet crop. However, the genetic and molecular regulatory mechanisms governing sorghum grain development and the associated agronomic traits remain unexplored. In this study, we performed a comprehensive transcriptomic analysis of pistils collected 1-2 days before pollination, and developing seeds collected -2, 10, 20 and 30 days after pollination of S. bicolor variety M35-1. Out of 31 337 genes expressed in these stages, 12 804 were differentially expressed in the consecutive stages of seed development. These exhibited 10 dominant expression patterns correlated with the distinct pathways and gene functions. Functional analysis, based on the pathway mapping, transcription factor enrichment and orthology, delineated the key patterns associated with pollination, fertilization, early seed development, grain filling and seed maturation. Furthermore, colocalization with previously reported quantitative trait loci (QTLs) for grain weight/size revealed 48 differentially expressed genes mapping to these QTL regions. Comprehensive literature mining integrated with QTL mapping and expression data shortlisted 25, 17 and 8 core candidates for engineering grain size, starch and protein content, respectively.

OsSPL11 positively regulates grain size by activating the expression of GW5L in rice

KEY MESSAGE

Rice OsSPL11 activates the expression of GW5L through binding to its promoter and positively regulates grain size. Grain size (GS) is an important determinant of grain weight and yield potential in cereal. Here, we report the functional analysis of OsSPL11 in grain length (GL), grain width (GW), and 1000-grain weight (TGW). OsSPL11 mutant plants, osspl11 lines, exhibited a decrease in GL, GW, and TGW, and OsSPL11-OE lines showed an increase in GL and TGW. Expression analysis revealed that OsSPL11 was located in the nucleus and highly expressed in spikelet hull and young development grains, consistent with its function in determining GS. Further analysis confirmed that OsSPL11 directly activates the expression of GW5L to regulate GS, meanwhile OsSPL11 expression is negatively regulated by OsGBP3. Taken together, our findings demonstrate that OsSPL11 could be a key regulator of affecting GS during the spikelet hull development and facilitate the process of improving grain yield by GS modification in rice.

Improving Rice Grain Quality Through Ecotype Breeding for Enhancing Food and Nutritional Security in Asia-Pacific Region

Rice grain is widely consumed as a staple food, providing essential nutrition for households, particularly marginalized families. It plays a crucial role in ensuring food security, promoting human nutrition, supporting good health, and contributing to global food and nutritional security. Addressing the diverse quality demands of emerging diverse and climate-risked population dietary needs requires the development of a single variety of rice grain that can meet the various dietary and nutritional requirements. However, there is a lack of concrete definition for rice grain quality, making it challenging to cater to the different demands. The lack of sufficient genetic study and development in improving rice grain quality has resulted in widespread malnutrition, hidden hunger, and micronutrient deficiencies affecting a significant portion of the global population. Therefore, it is crucial to identify genetically evolved varieties with marked qualities that can help address these issues. Various factors account for the declining quality of rice grain and requires further study to improve their quality for healthier diets. We characterized rice grain quality using Lancastrians descriptor and a multitude of intrinsic and extrinsic quality traits. Next, we examined various components of rice grain quality favored in the Asia-Pacific region. This includes preferences by different communities, rice industry stakeholders, and value chain actors. We also explored the biological aspects of rice grain quality in the region, as well as specific genetic improvements that have been made in these traits. Additionally, we evaluated the factors that can influence rice grain quality and discussed the future directions for ensuring food and nutritional security and meeting consumer demands for grain quality. We explored the diverse consumer bases and their varied preferences in Asian-Pacific countries including India, China, Nepal, Bhutan, Vietnam, Sri Lanka, Pakistan, Thailand, Cambodia, Philippines, Bangladesh, Indonesia, Korea, Myanmar and Japan. The quality preferences encompassed a range of factors, including rice head recovery, grain shape, uniform size before cooking, gelatinization, chalkiness, texture, amylose content, aroma, red-coloration of grain, soft and shine when cooked, unbroken when cooked, gelatinization, less water required for cooking, gelatinization temperature (less cooking time), aged rice, firm and dry when cooked (gel consistency), extreme white, soft when chewed, easy-to-cook rice (parboiled rice), vitamins, and minerals. These preferences were evaluated across high, low, and medium categories. A comprehensive analysis is provided on the enhancement of grain quality traits, including brown rice recovery, recovery rate of milled rice, head rice recovery, as well as morphological traits such as grain length, grain width, grain length-width ratio, and grain chalkiness. We also explored the characteristics of amylose, gel consistency, gelatinization temperature, viscosity, as well as the nutritional qualities of rice grains such as starch, protein, lipids, vitamins, minerals, phytochemicals, and bio-fortification potential. The various factors that impact the quality of rice grains, including pre-harvest, post-harvest, and genotype considerations were explored. Additionally, we discussed the future direction and genetic strategies to effectively tackle these challenges. These qualitative characteristics represent the fundamental focus of regional and national breeding strategies employed by different countries to meet consumer preference. Given the significance of rice as a staple food in Asia-Pacific countries, it is primarily consumed domestically, with only a small portion being exported internationally. All the important attributes must be clearly defined within specific parameters. It is crucial for geneticists and breeders to develop a rice variety that can meet the diverse demands of consumers worldwide by incorporating multiple desirable traits. Thus, the goal of addressing global food and nutritional security, and human healthy can be achieved.

Molecular mechanisms controlling grain size and weight and their biotechnological breeding applications in maize and other cereal crops

BACKGROUND

Cereal crops are a primary energy source for humans. Grain size and weight affect both evolutionary fitness and grain yield of cereals. Although studies on gene mining and molecular mechanisms controlling grain size and weight are constantly emerging in cereal crops, only a few systematic reviews on the underlying molecular mechanisms and their breeding applications are available so far.

AIM OF REVIEW

This review provides a general state-of-the-art overview of molecular mechanisms and targeted strategies for improving grain size and weight of cereals as well as insights for future yield-improving biotechnology-assisted breeding.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this review, the evolution of research on grain size and weight over the last 20 years is traced based on a bibliometric analysis of 1158 publications and the main signaling pathways and transcriptional factors involved are summarized. In addition, the roles of post-transcriptional regulation and photosynthetic product accumulation affecting grain size and weight in maize and rice are outlined. State-of-the-art strategies for discovering novel genes related to grain size and weight in maize and other cereal crops as well as advanced breeding biotechnology strategies being used for improving yield including marker-assisted selection, genomic selection, transgenic breeding, and genome editing are also discussed.

The OsMOB1A-OsSTK38 kinase complex phosphorylates CYCLIN C, controlling grain size and weight in rice

Grain size and weight are crucial yield-related traits in rice (Oryza sativa). Although certain key genes associated with rice grain size and weight have been successfully cloned, the molecular mechanisms underlying grain size and weight regulation remain elusive. Here, we identified a molecular pathway regulating grain size and weight in rice involving the MPS ONE BINDER KINASE ACTIVATOR-LIKE 1A-SERINE/THREONINE-PROTEIN KINASE 38-CYCLIN C (OsMOB1A-OsSTK38-OsCycC) module. OsSTK38 is a nuclear Dbf2-related kinase that positively regulates grain size and weight by coordinating cell proliferation and expansion in the spikelet hull. OsMOB1A interacts with and enhances the autophosphorylation of OsSTK38. Specifically, the critical role of the OsSTK38 S322 site in its kinase activity is highlighted. Furthermore, OsCycC, a component of the Mediator complex, was identified as a substrate of OsSTK38, with enhancement by OsMOB1A. Notably, OsSTK38 phosphorylates the T33 site of OsCycC. The phosphorylation of OsCycC by OsSTK38 influenced its interaction with the transcription factor KNOTTED-LIKE HOMEOBOX OF ARABIDOPSIS THALIANA 7 (OsKNAT7). Genetic analysis confirmed that OsMOB1A, OsSTK38, and OsCycC function in a common pathway to regulate grain size and weight. Taken together, our findings revealed a connection between the Hippo signaling pathway and the cyclin-dependent kinase module in eukaryotes. Moreover, they provide insights into the molecular mechanisms linked to yield-related traits and propose innovative breeding strategies for high-yielding varieties.

OsLCD3 interacts with OsSAMS1 to regulate grain size via ethylene/polyamine homeostasis control

A fundamental question in developmental biology is how to regulate grain size to improve crop yields. Despite this, little is still known about the genetics and molecular mechanisms regulating grain size in crops. Here, we provide evidence that a putative protein kinase-like (OsLCD3) interacts with the S-adenosyl-L-methionine synthetase 1 (OsSAMS1) and determines the size and weight of grains. OsLCD3 mutation (lcd3) significantly increased grain size and weight by promoting cell expansion in spikelet hull, whereas its overexpression caused negative effects, suggesting that grain size was negatively regulated by OsLCD3. Importantly, lcd3 and OsSAMS1 overexpression (SAM1OE) led to large and heavy grains, with increased ethylene and decreased polyamines production. Based on genetic analyses, it appears that OsLCD3 and OsSAMS1 control rice grain size in part by ethylene/polyamine homeostasis. The results of this study provide a genetic and molecular understanding of how the OsLCD3-OsSAMS1 regulatory module regulates grain size, suggesting that ethylene/polyamine homeostasis is an appropriate target for improving grain size and weight.

MtPIN4 plays critical roles in amino acid biosynthesis and metabolism of seed in Medicago truncatula

The regulation of seed development is critical for determining crop yield. Auxins are vital phytohormones that play roles in various aspects of plant growth and development. However, its role in amino acid biosynthesis and metabolism in seeds is not fully understood. In this study, we identified a mutant with small seeds through forward genetic screening in Medicago truncatula. The mutated gene encodes MtPIN4, an ortholog of PIN1. Using molecular approaches and integrative omics analyses, we discovered that auxin and amino acid content significantly decreased in mtpin4 seeds, highlighting the role of MtPIN4-mediated auxin distribution in amino acid biosynthesis and metabolism. Furthermore, genetic analysis revealed that the three orthologs of PIN1 have specific and overlapping functions in various developmental processes in M. truncatula. Our findings emphasize the significance of MtPIN4 in seed development and offer insights into the molecular mechanisms governing the regulation of seed size in crops. This knowledge could be applied to enhance crop quality by targeted manipulation of seed protein regulatory pathways.

Natural variation in MORE GRAINS 1 regulates grain number and grain weight in rice

Grain yield is determined mainly by grain number and grain weight. In this study, we identified and characterized MORE GRAINS1 (MOG1), a gene associated with grain number and grain weight in rice (Oryza sativa L.), through map-based cloning. Overexpression of MOG1 increased grain yield by 18.6%-22.3% under field conditions. We determined that MOG1, a bHLH transcription factor, interacts with OsbHLH107 and directly activates the expression of LONELY GUY (LOG), which encodes a cytokinin-activating enzyme and the cell expansion gene EXPANSIN-LIKE1 (EXPLA1), positively regulating grain number per panicle and grain weight. Natural variations in the promoter and coding regions of MOG1 between Hap-LNW and Hap-HNW alleles resulted in changes in MOG1 expression level and transcriptional activation, leading to functional differences. Haplotype analysis revealed that Hap-HNW, which results in a greater number and heavier grains, has undergone strong selection but has been poorly utilized in modern lowland rice breeding. In summary, the MOG1-OsbHLH107 complex activates LOG and EXPLA1 expression to promote cell expansion and division of young panicles through the cytokinin pathway, thereby increasing grain number and grain weight. These findings suggest that Hap-HNW could be used in strategies to breed high-yielding temperate japonica lowland rice.

When Size Matters: New Insights on How Seed Size Can Contribute to the Early Stages of Plant Development

The seed habit is the most complex and successful method of sexual reproduction in vascular plants. It represents a remarkable moment in the evolution of plants that afterward spread on land. In particular, seed size had a pivotal role in evolutionary success and agronomic traits, especially in the field of crop domestication. Given that crop seeds constitute one of the primary products for consumption, it follows that seed size represents a fundamental determinant of crop yield. This adaptative feature is strictly controlled by genetic traits from both maternal and zygotic tissues, although seed development and growth are also affected by environmental cues. Despite being a highly exploited topic for both basic and applied research, there are still many issues to be elucidated for developmental biology as well as for agronomic science. This review addresses a number of open questions related to cues that influence seed growth and size and how they influence seed germination. Moreover, new insights on the genetic-molecular control of this adaptive trait are presented.

Discovering New QTNs and Candidate Genes Associated with Rice-Grain-Related Traits within a Collection of Northeast Core Set and Rice Landraces

Grain-related traits are pivotal in rice cultivation, influencing yield and consumer preference. The complex inheritance of these traits, involving multiple alleles contributing to their expression, poses challenges in breeding. To address these challenges, a multi-locus genome-wide association study (ML-GWAS) utilizing 35,286 high-quality single-nucleotide polymorphisms (SNPs) was conducted. Our study utilized an association panel comprising 483 rice genotypes sourced from a northeast core set and a landraces set collected from various regions in India. Forty quantitative trait nucleotides (QTNs) were identified, associated with four grain-related traits: grain length (GL), grain width (GW), grain aroma (Aro), and length-width ratio (LWR). Notably, 16 QTNs were simultaneously identified using two ML-GWAS methods, distributed across multiple chromosomes. Nearly 258 genes were found near the 16 significant QTNs. Gene annotation study revealed that sixty of these genes exhibited elevated expression levels in specific tissues and were implicated in pathways influencing grain quality. Gene ontology (GO), trait ontology (TO), and enrichment analysis pinpointed 60 candidate genes (CGs) enriched in relevant GO terms. Among them, LOC_Os05g06470, LOC_Os06g06080, LOC_Os08g43470, and LOC_Os03g53110 were confirmed as key contributors to GL, GW, Aro, and LWR. Insights from QTNs and CGs illuminate rice trait regulation and genetic connections, offering potential targets for future studies.

Rice Big Grain1 improves grain yield in ectopically expressing rice and heterologously expressing tobacco plants

Functional genomics through transgenesis has provided faster and more reliable methods for identifying, characterizing, and utilizing genes or quantitative trait loci linked to agronomic traits to target yield. The present study explored the role of Big Grain1 (BG1) gene of rice (Oryza sativa L.) in yield improvement of crop plants. We aimed to identify the genetic variation of OsBG1 in various indica rice cultivars by studying the allelic polymorphism of the gene, while also investigating the gene's potential to increase crop yield through the transgenic approach. Our study reports the presence of an extra 393 bp sequence having two 6 bp enhancer elements in the 3' regulatory sequence of OsBG1 in the large-grain cultivar IR64 but not in the small-grain cultivar Badshahbhog. A single copy of the OsBG1 gene in both the cultivars and a 4.1-fold higher expression of OsBG1 in IR64 than in Badshahbhog imply that the grain size is positively correlated with the level of OsBG1 expression in rice. The ectopic expression of OsBG1 under the endosperm-specific glutelin C promoter in Badshahbhog enhanced the flag leaf length, panicle weight, and panicle length by an average of 33.2%, 33.7%, and 30.5%, respectively. The length of anthers, spikelet fertility, and grain yield per plant increased in transgenic rice lines by an average of 27.5%, 8.3%, and 54.4%, respectively. Heterologous expression of OsBG1 under the constitutive 2xCaMV35S promoter improved the number of seed pods per plant and seed yield per plant in transgenic tobacco lines by an average of 2.2-fold and 2.6-fold, respectively. Improving crop yield is crucial to ensure food security and socio-economic stability, and identifying suitable genetic factor is the essential step towards this endeavor. Our findings suggest that the OsBG1 gene is a promising candidate for improving the grain yield of monocot and dicot plant systems by molecular breeding and genetic engineering.

Comparative transcriptome analysis of vegetable soybean grain discloses genes essential for grain quality

BACKGROUND

Vegetable soybean is an important vegetable crop in world. Seed size and soluble sugar content are considered crucial indicators of quality in vegetable soybean, and there is a lack of clarity on the molecular basis of grain quality in vegetable soybean.

RESULTS

In this context, we performed a comprehensive comparative transcriptome analysis of seeds between a high-sucrose content and large-grain variety (Zhenong 6, ZN6) and a low-sucrose content and small-grain variety (Williams 82, W82) at three developmental stages, i.e. stage R5 (Beginning Seed), stage R6 (Full Seed), and stage R7 (Beginning Maturity). The transcriptome analysis showed that 17,107 and 13,571 differentially expressed genes (DEGs) were identified in ZN6 at R6 (vs. R5) and R7 (vs. R6), respectively, whereas 16,203 and 16,032 were detected in W82. Gene expression pattern and DEGs functional enrichment proposed genotype-specific biological processes during seed development. The genes participating in soluble sugar biosynthesis such as FKGP were overexpressed in ZN6, whereas those responsible for lipid and protein metabolism such as ALDH3 were more enhanced in W82, exhibiting different dry material accumulation between two genotypes. Furthermore, hormone-associated transcriptional factors involved in seed size regulation such as BEH4 were overrepresented in ZN6, exhibiting different seed size regulation processes between two genotypes.

CONCLUSIONS

Herein, we not only discovered the differential expression of genes encoding metabolic enzymes involved in seed composition, but also identified a type of hormone-associated transcriptional factors overexpressed in ZN6, which may regulate seed size and soluble content. This study provides new insights into the underlying causes of differences in the soybean metabolites and appearance, and suggests that genetic data can be used to improve its appearance and textural quality.

Modulation of histone acetylation enables fully mechanized hybrid rice breeding

Hybrid rice has achieved high grain yield and greatly contributes to food security, but the manual-labour-intensive hybrid seed production process limits fully mechanized hybrid rice breeding. For next-generation hybrid seed production, the use of small-grain male sterile lines to mechanically separate small hybrid seeds from mixed harvest is promising. However, it is difficult to find ideal grain-size genes for breeding ideal small-grain male sterile lines without penalties in the number of hybrid seeds and hybrid rice yield. Here we report that the use of small-grain alleles of the ideal grain-size gene GSE3 in male sterile lines enables fully mechanized hybrid seed production and dramatically increases hybrid seed number in three-line and two-line hybrid rice systems. The GSE3 gene encodes a histone acetyltransferase that binds histones and influences histone acetylation levels. GSE3 is recruited by the transcription factor GS2 to the promoters of their co-regulated grain-size genes and influences the histone acetylation status of their co-regulated genes. Field trials demonstrate that genome editing of GSE3 can be used to immediately improve current elite male sterile lines of hybrid rice for fully mechanized hybrid rice breeding, providing a new perspective for mechanized hybrid breeding in other crops.

QTL Analysis for Rice Quality-Related Traits and Fine Mapping of qWCR3

The quality of rice, evaluated using multiple quality-related traits, is the main determinant of its market competitiveness. In this study, two japonica rice varieties with significant differences in quality-related traits were used as parents to construct two populations, BC3F2 and BC3F2:3, with Kongyu131 (KY131) as the recurrent parent. A genetic linkage map was constructed using the BC3F2 population based on 151 pairs of SSR/InDel polymorphic markers selected between the parents. Grain-shape-related traits (grain length GL, grain width GW, and length-to-width ratio LWR), chalkiness-related traits (white-core rate WCR, white-belly rate WBR, white-back rate BR, and chalkiness rate CR), and amylose content (AC) were investigated in the two populations in 2017 and 2018. Except for BR and CR, the traits showed similar characteristics with a normal distribution in both populations. Genetic linkage analysis was conducted for these quality-related traits, and a total of 37 QTLs were detected in the two populations. Further validation was performed on the newly identified QTLs with larger effects, and three grain shape QTLs and four chalkiness QTLs were successfully validated in different environments. One repeatedly validated QTL, qWCR3, was selected for fine mapping and was successfully narrowed down to a 100 kb region in which only two genes, LOC_0s03g45210 and LOC_0s03g45320, exhibited sequence variations between the parents. Furthermore, the variation of LOC_Os03g45210 leads to a frameshift mutation and premature protein termination. The results of this study provide a theoretical basis for positional cloning of the qWCR3 gene, thus offering new genetic resources for rice quality improvement.

A novel OsHB5-OsAPL-OsMADS27/OsWRKY102 regulatory module regulates grain size in rice

Grain size, a crucial trait that determines rice yield and quality, is typically regulated by multiple genes. Although numerous genes controlling grain size have been identified, the precise and dynamic regulatory network governing grain size is still not fully understood. In this study, we unveiled a novel regulatory module composed of OsHB5, OsAPL and OsMADS27/OsWRKY102, which plays a crucial role in modulating grain size in rice. As a positive regulator of grain size, OsAPL has been found to interact with OsHB5 both in vitro and in vivo. Through chromatin immunoprecipitation-sequencing, we successfully mapped two potential targets of OsAPL, namely OsMADS27, a positive regulator in grain size and OsWRKY102, a negative regulator in lignification that is also associated with grain size control. Further evidence from EMSA and chromatin immunoprecipitation-quantitative PCR experiments has shown that OsAPL acts as an upstream transcription factor that directly binds to the promoters of OsMADS27 and OsWRKY102. Moreover, EMSA and dual-luciferase reporter assays have indicated that the interaction between OsAPL and OsHB5 enhances the repressive effect of OsAPL on OsMADS27 and OsWRKY102. Collectively, our findings discovered a novel regulatory module, OsHB5-OsAPL-OsMADS27/OsWRKY102, which plays a significant role in controlling grain size in rice. These discoveries provide potential targets for breeding high-yield and high-quality rice varieties.

Dissection of quantitative trait nucleotides and candidate genes associated with agronomic and yield-related traits under drought stress in rapeseed varieties: integration of genome-wide association study and transcriptomic analysis

Introduction

An important strategy to combat yield loss challenge is the development of varieties with increased tolerance to drought to maintain production. Improvement of crop yield under drought stress is critical to global food security.

Methods

In this study, we performed multiomics analysis in a collection of 119 diverse rapeseed (Brassica napus L.) varieties to dissect the genetic control of agronomic traits in two watering regimes [well-watered (WW) and drought stress (DS)] for 3 years. In the DS treatment, irrigation continued till the 50% pod development stage, whereas in the WW condition, it was performed throughout the whole growing season.

Results

The results of the genome-wide association study (GWAS) using 52,157 single-nucleotide polymorphisms (SNPs) revealed 1,281 SNPs associated with traits. Six stable SNPs showed sequence variation for flowering time between the two irrigation conditions across years. Three novel SNPs on chromosome C04 for plant weight were located within drought tolerance-related gene ABCG16, and their pleiotropically effects on seed weight per plant and seed yield were characterized. We identified the C02 peak as a novel signal for flowering time, harboring 52.77% of the associated SNPs. The 288-kbps LD decay distance analysis revealed 2,232 candidate genes (CGs) associated with traits. The CGs BIG1-D, CAND1, DRG3, PUP10, and PUP21 were involved in phytohormone signaling and pollen development with significant effects on seed number, seed weight, and grain yield in drought conditions. By integrating GWAS and RNA-seq, 215 promising CGs were associated with developmental process, reproductive processes, cell wall organization, and response to stress. GWAS and differentially expressed genes (DEGs) of leaf and seed in the yield contrasting accessions identified BIG1-D, CAND1, and DRG3 genes for yield variation.

Discussion

The results of our study provide insights into the genetic control of drought tolerance and the improvement of marker-assisted selection (MAS) for breeding high-yield and drought-tolerant varieties.

Regulatory mechanism and molecular genetic dissection of rice (Oryza sativa L.) grain size

With the sharp increase of the global population, adequate food supply is a great challenge. Grain size is an essential determinant of rice yield and quality. It is a typical quantitative trait controlled by multiple genes. In this paper, we summarized the quantitative trait loci (QTL) that have been molecularly characterized and provided a comprehensive summary of the regulation mechanism and genetic pathways of rice grain size. These pathways include the ubiquitin-proteasome system, G-protein, mitogen-activated protein kinase, phytohormone, transcriptional factors, abiotic stress. In addition, we discuss the possible application of advanced molecular biology methods and reasonable breeding strategies, and prospective on the development of high-yielding and high-quality rice varieties using molecular biology techniques.

Enhancing rice panicle branching and grain yield through tissue-specific brassinosteroid inhibition

Crop yield potential is constrained by the inherent trade-offs among traits such as between grain size and number. Brassinosteroids (BRs) promote grain size, yet their role in regulating grain number is unclear. By deciphering the clustered-spikelet rice germplasm, we show that activation of the BR catabolic gene BRASSINOSTEROID-DEFICIENT DWARF3 (BRD3) markedly increases grain number. We establish a molecular pathway in which the BR signaling inhibitor GSK3/SHAGGY-LIKE KINASE2 phosphorylates and stabilizes OsMADS1 transcriptional factor, which targets TERMINAL FLOWER1-like gene RICE CENTRORADIALIS2. The tissue-specific activation of BRD3 in the secondary branch meristems enhances panicle branching, minimizing negative effects on grain size, and improves grain yield. Our study showcases the power of tissue-specific hormonal manipulation in dismantling the trade-offs among various traits and thus unleashing crop yield potential in rice.

Genome-wide association studies reveal novel loci for grain size in two-rowed barley (Hordeum vulgare L.)

KEY MESSAGE

SNP-based and InDel-based GWAS on multi-environment data identified genomic regions associated with barley grain size. Barley yield and quality are greatly influenced by grain size. Improving barley grain size in breeding programs requires knowledge of genetic loci and alleles in germplasm resources. In this study, a collection of 334 worldwide two-rowed barley accessions with extensive genetic diversity was evaluated for grain size including grain length (GL), grain width (GW), and thousand-grain weight (TGW) across six independent field trials. Significant differences were observed in genotype and environments for all measured traits. SNP- and InDel-based GWAS were applied to dissect the genetic architecture of grain size with an SLAF-seq strategy. Two approaches using the FarmCPU model revealed 38 significant marker-trait associations (MTAs) with PVE ranging from 0.01% to 20.68%. Among these MTAs, five were on genomic regions where no previously reported QTL for grain size. Superior alleles of TGW-associated SNP233060 and GL-associated InDel11006 exhibited significantly higher levels of phenotype. The significant MTAs could be used in marker-assisted selection breeding.

New insights into QTNs and potential candidate genes governing rice yield via a multi-model genome-wide association study

BACKGROUND

Rice (Oryza sativa L.) is one of the globally important staple food crops, and yield-related traits are prerequisites for improved breeding efficiency in rice. Here, we used six different genome-wide association study (GWAS) models for 198 accessions, with 553,229 single nucleotide markers (SNPs) to identify the quantitative trait nucleotides (QTNs) and candidate genes (CGs) governing rice yield.

RESULTS

Amongst the 73 different QTNs in total, 24 were co-localized with already reported QTLs or loci in previous mapping studies. We obtained fifteen significant QTNs, pathway analysis revealed 10 potential candidates within 100kb of these QTNs that are predicted to govern plant height, days to flowering, and plot yield in rice. Based on their superior allelic information in 20 elite and 6 inferior genotypes, we found a higher percentage of superior alleles in the elite genotypes in comparison to inferior genotypes. Further, we implemented expression analysis and enrichment analysis enabling the identification of 73 candidate genes and 25 homologues of Arabidopsis, 19 of which might regulate rice yield traits. Of these candidate genes, 40 CGs were found to be enriched in 60 GO terms of the studied traits for instance, positive regulator metabolic process (GO:0010929), intracellular part (GO:0031090), and nucleic acid binding (GO:0090079). Haplotype and phenotypic variation analysis confirmed that LOC_OS09G15770, LOC_OS02G36710 and LOC_OS02G17520 are key candidates associated with rice yield.

CONCLUSIONS

Overall, we foresee that the QTNs, putative candidates elucidated in the study could summarize the polygenic regulatory networks controlling rice yield and be useful for breeding high-yielding varieties.

Identification of qGL4.1 and qGL4.2, two closely linked QTL controlling grain length in rice

Grain size is an important appearance quality trait in rice, which also affects grain yield. In this study, a recombinant inbred line (RIL) population derived from a cross between indica variety 9311 and japonica variety Cypress was constructed. And 181 out of 600 RILs were sequenced, and a high-density genetic map containing 2842 bin markers was constructed, with a total map length of 1500.6 cM. A total of 10 quantitative trait loci (QTL) related to grain length (GL), grain width (GW), grain length-to-width ratio (LWR), and 1000-grain weight (TGW) were detected under two environments. The genetic effect of qGL4, a minor QTL for GL and TGW, was validated using three heterogeneous inbred family (HIF) segregation populations. It was further dissected into two closed linked QTL, qGL4.1 and qGL4.2. By progeny testing, qGL4.1 and qGL4.2 were successfully delimited to intervals of 1304-kb and 423-kb, respectively. Our results lay the foundation for the map-based cloning of qGL4.1 and qGL4.2 and provide new gene resources for the improvement of grain yield and quality in rice.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01447-y.

miRNAs and genes as molecular regulators of rice grain morphology and yield

Rice is one of the most consumed crops worldwide and the genetic and molecular basis of its grain yield attributes are well understood. Various studies have identified different yield-related parameters in rice that are regulated by the microRNAs (miRNAs). MiRNAs are endogenous small non-coding RNAs that silence gene expression during or after transcription. They control a variety of biological or genetic activities in plants including growth, development and response to stress. In this review, we have summarized the available information on the genetic control of panicle architecture and grain yield (number and morphology) in rice. The miRNA nodes that are associated with their regulation are also described while focussing on the central role of miR156-SPL node to highlight the co-regulation of two master regulators that determine the fate of panicle development. Since abiotic stresses are known to negatively affect yield, the impact of abiotic stress induced alterations on the levels of these miRNAs are also discussed to highlight the potential of miRNAs for regulating crop yields.

Triacylglycerol lipase, OsSG34, plays an important role in grain shape and appearance quality in rice

Optimal grain-appearance quality is largely determined by grain size. To date, dozens of grain size-related genes have been identified. However, the regulatory mechanism of slender grain formation is not fully clear. We identified the OsSG34 gene by map-based cloning. A 9-bp deletion on 5'-untranslated region of OsSG34, which resulted in the expression difference between the wild-type and sg34 mutant, led to the slender grains and good transparency in sg34 mutant. OsSG34 as an α/β fold triacylglycerol lipase affected the triglyceride content directly, and the components of cell wall indirectly, especially the lignin between the inner and outer lemmas in rice grains, which could affect the change in grain size by altering cell proliferation and expansion, while the change in starch content and starch granule arrangement in endosperm could affect the grain-appearance quality. Moreover, the OsERF71 was identified to directly bind to cis-element on the mutant site, thereby regulating the OsSG34 expression. Knockout of three OsSG34 homologous genes resulted in slender grains as well. The study demonstrated OsSG34, involved in lipid metabolism, affected grain size and quality. Our findings suggest that the OsSG34 gene could be used in rice breeding for high yield and good grain-appearance quality via marker-assisted selection and gene-editing approaches.

The RING-Type Domain-Containing Protein GNL44 Is Essential for Grain Size and Quality in Rice (Oryza sativa L.)

Grain size in rice (Oryza sativa L.) shapes yield and quality, but the underlying molecular mechanism is not fully understood. We functionally characterized GRAIN NUMBER AND LARGE GRAIN SIZE 44 (GNL44), encoding a RING-type protein that localizes to the cytoplasm. The gnl44 mutant has fewer but enlarged grains compared to the wild type. GNL44 is mainly expressed in panicles and developing grains. Grain chalkiness was higher in the gnl44 mutant than in the wild type, short-chain amylopectin content was lower, middle-chain amylopectin content was higher, and appearance quality was worse. The amylose content and gel consistency of gnl44 were lower, and protein content was higher compared to the wild type. Rapid Visco Analyzer results showed that the texture of cooked gnl44 rice changed, and that the taste value of gnl44 was lower, making the eating and cooking quality of gnl44 worse than that of the wild type. We used gnl44, qgl3, and gs3 monogenic and two-gene near-isogenic lines to study the effects of different combinations of genes affecting grain size on rice quality-related traits. Our results revealed additive effects for these three genes on grain quality. These findings enrich the genetic resources available for rice breeders.

Leveraging brassinosteroids towards the next Green Revolution

The use of gibberellin-related dwarfing genes significantly increased grain yield during the Green Revolution. Brassinosteroids (BRs) play a vital role in regulating agronomic traits and stress resistance. The potential of BR-related genes in crop improvement has been well demonstrated, positioning BRs as crucial targets for the next agricultural biotechnological revolution. However, BRs exert pleiotropic effects on plants, and thus present both opportunities and challenges for their application. Recent research suggests promising strategies for leveraging BR regulatory molecules for crop improvement, such as exploring function-specific genes, identifying beneficial alleles, inducing favorable mutations, and optimizing spatial hormone distribution. Advancing our understanding of the roles of BRs in plants is imperative to implement these strategies effectively.

Genome-wide survey, molecular evolution and expression analysis of Auxin Response Factor (ARF) gene family indicating their key role in seed number per pod in pigeonpea (C. cajan L. Millsp.)

Auxin Response Factors (ARF) are a family of transcription factors that mediate auxin signalling and regulate multiple biological processes. Their crucial role in increasing plant biomass/yield influenced this study, where a systematic analysis of ARF gene family was carried out to identify the key proteins controlling embryo/seed developmental pathways in pigeonpea. A genome-wide scan revealed the presence of 12 ARF genes in pigeonpea, distributed across the chromosomes 1, 3, 4, 8 and 11. Domain analysis of ARF proteins showed the presence of B3 DNA binding, AUX response, and IAA domains. Majority of them are of nuclear origin, and do not exhibit the level of genomic expansion as observed in Glycine max (51 members). The duplication events seem to range from 31.6 to 42.3 million years ago (mya). Promoter analysis revealed the presence of multiple cis-acting elements related to stress responses, hormone signalling and other development processes. The expression atlas data highlighted the expression of CcARF8 in hypocotyl, bud and flower whereas, CcARF7 expression was significantly high in pod. The real-time expression of CcARF2, CcARF3 and CcARF18 was highest in genotypes with high seed number indicating their key role in regulating embryo development and determining seed set in pigeonpea.

Identification of Superior Haplotypes and Haplotype Combinations for Grain Size- and Weight-Related Genes for Breeding Applications in Rice (Oryza sativa L.)

The identification of superior haplotypes and haplotype combinations is essential for haplotype-based breeding (HBB), which provides selection targets for genomics-assisted breeding. In this study, genotypes of 42 functional genes in rice were analyzed by targeted capture sequencing in a panel of 180 Indica rice accessions. In total, 69 SNPs/Indels in seven genes were detected to be associated with grain length (GL), grain width (GW), ratio of grain length-width (L/W) and thousand-grain weight (TGW) using candidate gene-based association analysis, including BG1 and GS3 for GL, GW5 for GW, BG1 and GW5 for L/W, and AET1, SNAC1, qTGW3, DHD1 and GW5 for TGW. Furthermore, two haplotypes were identified for each of the seven genes according to these associated SNPs/Indels, and the amount of genetic variation explained by different haplotypes ranged from 3.24% to 27.66%. Additionally, three, three and eight haplotype combinations for GL, L/W and TGW explained 25.38%, 5.5% and 22.49% of the total genetic variation for each trait, respectively. Further analysis showed that Minghui63 had the superior haplotype combination Haplotype Combination 4 (HC4) for TGW. The most interesting finding was that some widely used restorer lines derived from Minghui63 also have the superior haplotype combination HC4, and our breeding varieties and lines using the haplotype-specific marker panel also confirmed that the TGW of the lines was much higher than that of their sister lines without HC4, suggesting that TGW-HC4 is the superior haplotype combination for TGW and can be utilized in rice breeding.

Integration of genome-wide association study, linkage analysis, and population transcriptome analysis to reveal the TaFMO1-5B modulating seminal root growth in bread wheat

Bread wheat, one of the keystone crops for global food security, is challenged by climate change and resource shortage. The root system plays a vital role in water and nutrient absorption, making it essential for meeting the growing global demand. Here, using an association-mapping population composed of 406 accessions, we identified QTrl.Rs-5B modulating seminal root development with a genome-wide association study and validated its genetic effects with two F5 segregation populations. Transcriptome-wide association study prioritized TaFMO1-5B, a gene encoding the flavin-containing monooxygenases, as the causal gene for QTrl.Rs-5B, whose expression levels correlate negatively with the phenotyping variations among our population. The lines silenced for TaFMO1-5B consistently showed significantly larger seminal roots in different genetic backgrounds. Additionally, the agriculture traits measured in multiple environments showed that QTrl.Rs-5B also affects yield component traits and plant architecture-related traits, and its favorable haplotype modulates these traits toward that of modern cultivars, suggesting the application potential of QTrl.Rs-5B for wheat breeding. Consistently, the frequency of the favorable haplotype of QTrl.Rs-5B increased with habitat expansion and breeding improvement of bread wheat. In conclusion, our findings identified and demonstrated the effects of QTrl.Rs-5B on seminal root development and illustrated that it is a valuable genetic locus for wheat root improvement.

A CYP78As-small grain4-coat protein complex Ⅱ pathway promotes grain size in rice

CYP78A, a cytochrome P450 subfamily that includes rice (Oryza sativa L.) BIG GRAIN2 (BG2, CYP78A13) and Arabidopsis thaliana KLUH (KLU, CYP78A5), generate an unknown mobile growth signal (referred to as a CYP78A-derived signal) that increases grain (seed) size. However, the mechanism by which the CYP78A pathway increases grain size remains elusive. Here, we characterized a rice small grain mutant, small grain4 (smg4), with smaller grains than its wild type due to restricted cell expansion and cell proliferation in spikelet hulls. SMG4 encodes a multidrug and toxic compound extrusion (MATE) transporter. Loss of function of SMG4 causes smaller grains while overexpressing SMG4 results in larger grains. SMG4 is mainly localized to endoplasmic reticulum (ER) exit sites (ERESs) and partially localized to the ER and Golgi. Biochemically, SMG4 interacts with coat protein complex Ⅱ (COPⅡ) components (Sar1, Sec23, and Sec24) and CYP78As (BG2, GRAIN LENGTH 3.2 [GL3.2], and BG2-LIKE 1 [BG2L1]). Genetically, SMG4 acts, at least in part, in a common pathway with Sar1 and CYP78As to regulate grain size. In summary, our findings reveal a CYP78As-SMG4-COPⅡ regulatory pathway for grain size in rice, thus providing new insights into the molecular and genetic regulatory mechanism of grain size.

SMALL PLANT AND ORGAN 1 (SPO1) Encoding a Cellulose Synthase-like Protein D4 (OsCSLD4) Is an Important Regulator for Plant Architecture and Organ Size in Rice

Plant architecture and organ size are considered as important traits in crop breeding and germplasm improvement. Although several factors affecting plant architecture and organ size have been identified in rice, the genetic and regulatory mechanisms remain to be elucidated. Here, we identified and characterized the small plant and organ 1 (spo1) mutant in rice (Oryza sativa), which exhibits narrow and rolled leaf, reductions in plant height, root length, and grain width, and other morphological defects. Map-based cloning revealed that SPO1 is allelic with OsCSLD4, a gene encoding the cellulose synthase-like protein D4, and is highly expressed in the roots at the seedling and tillering stages. Microscopic observation revealed the spo1 mutant had reduced number and width in leaf veins, smaller size of leaf bulliform cells, reduced cell length and cell area in the culm, and decreased width of epidermal cells in the outer glume of the grain. These results indicate the role of SPO1 in modulating cell division and cell expansion, which modulates plant architecture and organ size. It is showed that the contents of endogenous hormones including auxin, abscisic acid, gibberellin, and zeatin tested in the spo1 mutant were significantly altered, compared to the wild type. Furthermore, the transcriptome analysis revealed that the differentially expressed genes (DEGs) are significantly enriched in the pathways associated with plant hormone signal transduction, cell cycle progression, and cell wall formation. These results indicated that the loss of SPO1/OsCSLD4 function disrupted cell wall cellulose synthase and hormones homeostasis and signaling, thus leading to smaller plant and organ size in spo1. Taken together, we suggest the functional role of SPO1/OsCSLD4 in the control of rice plant and organ size by modulating cell division and expansion, likely through the effects of multiple hormonal pathways on cell wall formation.

Genetic Basis of Grain Size and Weight in Rice, Wheat, and Barley

Grain size is a key component of grain yield in cereals. It is a complex quantitative trait controlled by multiple genes. Grain size is determined via several factors in different plant development stages, beginning with early tillering, spikelet formation, and assimilates accumulation during the pre-anthesis phase, up to grain filling and maturation. Understanding the genetic and molecular mechanisms that control grain size is a prerequisite for improving grain yield potential. The last decade has brought significant progress in genomic studies of grain size control. Several genes underlying grain size and weight were identified and characterized in rice, which is a model plant for cereal crops. A molecular function analysis revealed most genes are involved in different cell signaling pathways, including phytohormone signaling, transcriptional regulation, ubiquitin-proteasome pathway, and other physiological processes. Compared to rice, the genetic background of grain size in other important cereal crops, such as wheat and barley, remains largely unexplored. However, the high level of conservation of genomic structure and sequences between closely related cereal crops should facilitate the identification of functional orthologs in other species. This review provides a comprehensive overview of the genetic and molecular bases of grain size and weight in wheat, barley, and rice, focusing on the latest discoveries in the field. We also present possibly the most updated list of experimentally validated genes that have a strong effect on grain size and discuss their molecular function.

Molecular, genetic, and genomic basis of seed size and yield characteristics in soybean

Soybean (Glycine max L. Merr.) is a crucial oilseed cash crop grown worldwide and consumed as oil, protein, and food by humans and feed by animals. Comparatively, soybean seed yield is lower than cereal crops, such as maize, rice, and wheat, and the demand for soybean production does not keep up with the increasing consumption level. Therefore, increasing soybean yield per unit area is the most crucial breeding objective and is challenging for the scientific community. Moreover, yield and associated traits are extensively researched in cereal crops, but little is known about soybeans' genetics, genomics, and molecular regulation of yield traits. Soybean seed yield is a complex quantitative trait governed by multiple genes. Understanding the genetic and molecular processes governing closely related attributes to seed yield is crucial to increasing soybean yield. Advances in sequencing technologies have made it possible to conduct functional genomic research to understand yield traits' genetic and molecular underpinnings. Here, we provide an overview of recent progress in the genetic regulation of seed size in soybean, molecular, genetics, and genomic bases of yield, and related key seed yield traits. In addition, phytohormones, such as auxin, gibberellins, cytokinins, and abscisic acid, regulate seed size and yield. Hence, we also highlight the implications of these factors, challenges in soybean yield, and seed trait improvement. The information reviewed in this study will help expand the knowledge base and may provide the way forward for developing high-yielding soybean cultivars for future food demands.

Rice Big Grain1 enhances biomass and plant growth-promoting traits in rhizospheric yeast Candida tropicalis

The Big Grain1 (BG1) gene of rice (Oryza sativa L.) is reported to increase the yield of rice crops; however, its molecular mechanism is largely concealed. To explore its functional prospects, we have taken a structure-function-based approach. In silico analyses suggest OsBG1 is a DNA- and phytohormone-binding protein. Heterologous expression of OsBG1 with galactose-inducible promoter GAL1p in the rhizospheric yeast Candida tropicalis SY005 revealed 7.9- and 1.5-fold higher expression of the gene at 12 and 24 h, respectively, compared to the expression at 36 h post-galactose induction. Functional activity of the induced OsBG1 in engineered yeast increased cell density, specific growth rate, and biomass by 28.5%, 29.8%, and 14.1%, respectively, and decreased the generation time by 21.25%. Flow cytometry-based cell cycle analysis of OsBG1-expressing yeast cells exhibited an increase in the cells of the G2/M population by 15.8% after 12 h of post-galactose induction. The gene expression study of yeast transformants disclosed that OsBG1 regulates cell division by upregulating the expression of the endogenous gene cyclin B1 (CtCYB1) by 1.3- and 1.9-folds at 10 and 12 h, respectively, compared to the control, and is positively influenced by the phytohormone indole acetic acid (IAA). Further, the study revealed that OsBG1 significantly increases biofilm formation, stress tolerance, and IAA production in C. tropicalis SY005, implying its prospective role in enhancing plant growth-promoting traits in microbes. OsBG1-expressing rhizospheric yeast cells significantly improved the germination and growth parameters of the bio-inoculated rice seeds. Altogether, this study suggests OsBG1 can be employed to genetically improve suitable bio-inoculants for their plant growth-promoting traits to augment crop productivity. KEY POINTS: • In silico analyses suggested OsBG1 is a phytohormone-binding transcription factor. • OsBG1 enhanced growth in rhizospheric Candida tropicalis by upregulating CtCYB1. • OsBG1 improved plant growth-promoting traits of the rhizospheric yeast C. tropicalis.

QTL mapping for kernel-related traits in a durum wheat x T. dicoccum segregating population

Durum wheat breeding relies on grain yield improvement to meet its upcoming demand while coping with climate change. Kernel size and shape are the determinants of thousand kernel weight (TKW), which is a key component of grain yield, and the understanding of the genetic control behind these traits supports the progress in yield potential. The present study aimed to dissect the genetic network responsible for kernel size components (length, width, perimeter, and area) and kernel shape traits (width-to-length ratio and formcoefficient) as well as their relationships with kernel weight, plant height, and heading date in durum wheat. Quantitative Trait Locus (QTL) mapping was performed on a segregating population of 110 recombinant inbred lines, derived from a cross between the domesticated emmer wheat accession MG5323 and the durum wheat cv. Latino, evaluated in four different environments. A total of 24 QTLs stable across environments were found and further grouped in nine clusters on chromosomes 2A, 2B, 3A, 3B, 4B, 6B, and 7A. Among them, a QTL cluster on chromosome 4B was associated with kernel size traits and TKW, where the parental MG5323 contributed the favorable alleles, highlighting its potential to improve durum wheat germplasm. The physical positions of the clusters, defined by the projection on the T. durum reference genome, overlapped with already known genes (i.e., BIG GRAIN PROTEIN 1 on chromosome 4B). These results might provide genome-based guidance for the efficient exploitation of emmer wheat diversity in wheat breeding, possibly through yield-related molecular markers.

The miR167-OsARF12 module regulates rice grain filling and grain size downstream of miR159

Grain weight and quality are always determined by grain filling. Plant microRNAs have drawn attention as key targets for regulation of grain size and yield. However, the mechanisms that underlie grain size regulation remain largely unclear because of the complex networks that control this trait. Our earlier studies demonstrated that suppressed expression of miR167 (STTM/MIM167) substantially increased grain weight. In a field test, the yield increased up to 12.90%-21.94% because of a significantly enhanced grain filling rate. Here, biochemical and genetic analyses revealed the regulatory effects of miR159 on miR167 expression. Further analysis indicated that OsARF12 is the major mediator by which miR167 regulates rice grain filling. Overexpression of OsARF12 produced grain weight and grain filling phenotypes resembling those of STTM/MIM167 plants. Upon in-depth analysis, we found that OsARF12 activates OsCDKF;2 expression by directly binding to the TGTCGG motif in its promoter region. Flow cytometry analysis of young panicles from OsARF12-overexpressing plants and examination of cell number in cdkf;2 mutants verified that OsARF12 positively regulates grain filling and grain size by targeting OsCDKF;2. Moreover, RNA sequencing results suggested that the miR167-OsARF12 module is involved in the cell development process and hormone pathways. OsARF12-overexpressing plants and cdkf;2 mutants exhibited enhanced and reduced sensitivity to exogenous auxin and brassinosteroid (BR) treatment, confirming that targeting of OsCDKF;2 by OsARF12 mediates auxin and BR signaling. Our results reveal that the miR167-OsARF12 module works downstream of miR159 to regulate rice grain filling and grain size via OsCDKF;2 by controlling cell division and mediating auxin and BR signals.

SLG2 specifically regulates grain width through WOX11-mediated cell expansion control in rice

Grain size is specified by three dimensions of length, width and thickness, and slender grain is a desirable quality trait in rice. Up to now, many grain size regulators have been identified. However, most of these molecules show influence on multi-dimensions of grain development, and only a few of them function specifically in grain width, a key factor determining grain yield and appearance quality. In this study, we identify the SLG2 (SLENDER GUY2) gene that specifically regulates grain width by affecting cell expansion in the spikelet hulls. SLG2 encodes a WD40 domain containing protein, and our biochemical analyses show that SLG2 acts as a transcription activator of its interacting WOX family protein WOX11. We demonstrate that the SLG2-associated WOX11 binds directly to the promoter of OsEXPB7, one of the downstream cell expansion genes. We show that knockout of WOX11 results in plants with a slender grain phenotype similar to the slg2 mutant. We also present that finer grains with different widths could be produced by combining SLG2 with the grain width regulator GW8. Collectively, we uncover the crucial role of SLG2 in grain width control, and provide a promising route to design rice plants with better grain shape and quality.

Global Transcriptome and Co-Expression Network Analyses Revealed Hub Genes Controlling Seed Size/Weight and/or Oil Content in Peanut

Cultivated peanut (Arachis hypogaea L.) is an important economic and oilseed crop worldwide, providing high-quality edible oil and high protein content. Seed size/weight and oil content are two important determinants of yield and quality in peanut breeding. To identify key regulators controlling these two traits, two peanut cultivars with contrasting phenotypes were compared to each other, one having a larger seed size and higher oil content (Zhonghua16, ZH16 for short), while the second cultivar had smaller-sized seeds and lower oil content (Zhonghua6, ZH6). Whole transcriptome analyses were performed on these two cultivars at four stages of seed development. The results showed that ~40% of the expressed genes were stage-specific in each cultivar during seed development, especially at the early stage of development. In addition, we identified a total of 5356 differentially expressed genes (DEGs) between ZH16 and ZH6 across four development stages. Weighted gene co-expression network analysis (WGCNA) based on DEGs revealed multiple hub genes with potential roles in seed size/weight and/or oil content. These hub genes were mainly involved in transcription factors (TFs), phytohormones, the ubiquitin-proteasome pathway, and fatty acid synthesis. Overall, the candidate genes and co-expression networks detected in this study could be a valuable resource for genetic breeding to improve seed yield and quality traits in peanut.

OsCBL5-CIPK1-PP23 module enhances rice grain size and weight through the gibberellin pathway

Grain size is a key factor in determining rice (Oryza sativa) yield, and exploring new pathways to regulate grain size has immense potential to improve yield. In this study, we report that OsCBL5 encodes a calcineurin B subunit protein that significantly promotes grain size and weight. oscbl5 plants produced obviously smaller and lighter seeds. We further revealed that OsCBL5 promotes grain size by affecting cell expansion in the spikelet hull. Biochemical analyses demonstrated that CBL5 interacts with CIPK1 and PP23. Furthermore, double and triple mutations were induced using CRISPR/Cas9 (cr) to analyze the genetic relationship. It was found that the cr-cbl5/cipk1 phenotype was similar to that of cr-cipk1 and that the cr-cbl5/pp23, cr-cipk1/pp23, and cr-cbl5/cipk1/pp23 phenotype was similar to that of cr-pp23, indicating that OsCBL5, CIPK1, and PP23 act as a molecular module influencing seed size. In addition, the results show that both CBL5 and CIPK1 are involved in the gibberellic acid (GA) pathway and significantly affect the accumulation of endogenous active GA4 . PP23 participates in GA signal transduction. In brief, this study identified a new module that affects rice grain size, OsCBL5-CIPK1-PP23, which could potentially be targeted to improve rice yield.

Fine Mapping and Candidate Gene Analysis of Rice Grain Length QTL qGL9.1

Grain length (GL) is one of the crucial determinants of rice yield and quality. However, there is still a shortage of knowledge on the major genes controlling the inheritance of GL in japonica rice, which severely limits the improvement of japonica rice yields. Here, we systemically measured the GL of 667 F₂ and 1570 BC₃F₃ individuals derived from two cultivated rice cultivars, Pin20 and Songjing15, in order to identify the major genomic regions associated with GL. A novel major QTL, qGL9.1, was mapped on chromosome 9, which is associated with the GL, using whole-genome re-sequencing with bulked segregant analysis. Local QTL linkage analysis with F₂ and fine mapping with the recombinant plant revealed a 93-kb core region on qGL9.1 encoding 15 protein-coding genes. Only the expression level of LOC_Os09g26970 was significantly different between the two parents at different stages of grain development. Moreover, haplotype analysis revealed that the alleles of Pin20 contribute to the optimal GL (9.36 mm) and GL/W (3.31), suggesting that Pin20 is a cultivated species carrying the optimal GL variation of LOC_Os09g26970. Furthermore, a functional-type mutation (16398989-bp, G>A) located on an exon of LOC_Os09g26970 could be used as a molecular marker to distinguish between long and short grains. Our experiments identified LOC_Os09g26970 as a novel gene associated with GL in japonica rice. This result is expected to further the exploration of the genetic mechanism of rice GL and improve GL in rice japonica varieties by marker-assisted selection.

GS6.1 controls kernel size and plant architecture in rice

MAIN CONCLUSION

A novel QTL GS6.1 increases yield per plant by controlling kernel size, plant architecture, and kernel filling in rice. Kernel size and plant architecture are critical agronomic traits that greatly influence kernel yield in rice. Using the single-segment substitution lines (SSSLs) with an indica cultivar Huajingxian74 as a recipient parent and American Jasmine as a donor parent, we identified a novel quantitative trait locus (QTL), named GS6.1. Near isogenic line-GS6.1 (NIL-GS6.1) produces long and narrow kernels by regulating cell length and width in the spikelet hulls, thus increasing the 1000-kernel weight. Compared with the control, the plant height, panicles per plant, panicle length, kernels per plant, secondary branches per panicle, and yield per plant of NIL-GS6.1 are increased. In addition, GS6.1 regulates the kernel filling rate. GS6.1 controls kernel size by modulating the transcription levels of part of EXPANSINs, kernel filling-related genes, and kernel size-related genes. These results indicate that GS6.1 might be beneficial for improving kernel yield and plant architecture in rice breeding by molecular design.

Joint analysis of phenotype-effect-generation identifies loci associated with grain quality traits in rice hybrids

Genetic improvement of grain quality is more challenging in hybrid rice than in inbred rice due to additional nonadditive effects such as dominance. Here, we describe a pipeline developed for joint analysis of phenotypes, effects, and generations (JPEG). As a demonstration, we analyze 12 grain quality traits of 113 inbred lines (male parents), five tester lines (female parents), and 565 (113×5) of their hybrids. We sequence the parents for single nucleotide polymorphisms calling and infer the genotypes of the hybrids. Genome-wide association studies with JPEG identify 128 loci associated with at least one of the 12 traits, including 44, 97, and 13 loci with additive effects, dominant effects, and both additive and dominant effects, respectively. These loci together explain more than 30% of the genetic variation in hybrid performance for each of the traits. The JEPG statistical pipeline can help to identify superior crosses for breeding rice hybrids with improved grain quality.

Salicylic acid inhibits rice endocytic protein trafficking mediated by OsPIN3t and clathrin to affect root growth

Salicylic acid (SA) plays important roles in different aspects of plant development, including root growth, where auxin is also a major player by means of its asymmetric distribution. However, the mechanism underlying the effect of SA on the development of rice roots remains poorly understood. Here, we show that SA inhibits rice root growth by interfering with auxin transport associated with the OsPIN3t- and clathrin-mediated gene regulatory network (GRN). SA inhibits root growth as well as Brefeldin A-sensitive trafficking through a non-canonical SA signaling mechanism. Transcriptome analysis of rice seedlings treated with SA revealed that the OsPIN3t auxin transporter is at the center of a GRN involving the coat protein clathrin. The root growth and endocytic trafficking in both the pin3t and clathrin heavy chain mutants were SA insensitivity. SA inhibitory effect on the endocytosis of OsPIN3t was dependent on clathrin; however, the root growth and endocytic trafficking mediated by tyrphostin A23 (TyrA23) were independent of the pin3t mutant under SA treatment. These data reveal that SA affects rice root growth through the convergence of transcriptional and non-SA signaling mechanisms involving OsPIN3t-mediated auxin transport and clathrin-mediated trafficking as key components.

OsBBX19-OsBTB97/OsBBX11 module regulates spikelet development and yield production in rice

Spikelet and floral-related organs are important agronomic traits for rice grain yield. BTB (broad-complex, tram track, and bric-abrac) proteins control various developmental functions in plants; however, the molecular mechanism of BTB proteins underlying grain development and yield production is still unknown. Here, we evaluated the molecular mechanism of a previously unrecognized functional gene, namely OsBTB97 that regulates the floral and spikelet-related organs which greatly affect the final grain yield. We found that the knockdown of the OsBTB97 gene had significant impacts on the development of spikelet-related organs and grain size, resulting in a decrease in yield, by altering the transcript levels of various spikelet- and grain-related genes. Furthermore, we found that the knockout mutants of two BBX genes, OsBBX11 and OsBBX19, which interact with the OsBTB97 protein at translation and transcriptional level, respectively, displayed lower OsBTB97 expression, suggesting the genetic relationship between the BTB protein and the BBX transcription factors in rice. Taken together, our study dissects the function of the novel OsBTB97 by interacting with two BBX proteins and an OsBBX19-OsBTB97/OsBBX11 module might function in the spikelet development and seed production in rice. The outcome of the present study provides promising knowledge about BTB proteins in the improvement of crop production in plants.

Genetic dissection of thousand-seed weight in linseed (Linum usitatissimum L.) using multi-locus genome-wide association study

Flaxseed/linseed is an important oilseed crop having applications in the food, nutraceutical, and paint industry. Seed weight is one of the most crucial determinants of seed yield in linseed. Here, quantitative trait nucleotides (QTNs) associated with thousand-seed weight (TSW) have been identified using multi-locus genome-wide association study (ML-GWAS). Field evaluation was carried out in five environments in multi-year-location trials. SNP genotyping information of the AM panel of 131 accessions comprising 68,925 SNPs was employed for ML-GWAS. From the six ML-GWAS methods employed, five methods helped identify a total of 84 unique significant QTNs for TSW. QTNs identified in ≥ 2 methods/environments were designated as stable QTNs. Accordingly, 30 stable QTNs have been identified for TSW accounting up to 38.65% trait variation. Alleles with positive effect on trait were analyzed for 12 strong QTNs with r ² ≥ 10.00%, which showed significant association of specific alleles with higher trait value in three or more environments. A total of 23 candidate genes have been identified for TSW, which included B3 domain-containing transcription factor, SUMO-activating enzyme, protein SCARECROW, shaggy-related protein kinase/BIN2, ANTIAUXIN-RESISTANT 3, RING-type E3 ubiquitin transferase E4, auxin response factors, WRKY transcription factor, and CBS domain-containing protein. In silico expression analysis of candidate genes was performed to validate their possible role in different stages of seed development process. The results from this study provide significant insight and elevate our understanding on genetic architecture of TSW trait in linseed.

Can the Wild Perennial, Rhizomatous Rice Species Oryza longistaminata be a Candidate for De Novo Domestication?

As climate change intensifies, the development of resilient rice that can tolerate abiotic stresses is urgently needed. In nature, many wild plants have evolved a variety of mechanisms to protect themselves from environmental stresses. Wild relatives of rice may have abundant and virtually untapped genetic diversity and are an essential source of germplasm for the improvement of abiotic stress tolerance in cultivated rice. Unfortunately, the barriers of traditional breeding approaches, such as backcrossing and transgenesis, make it challenging and complex to transfer the underlying resilience traits between plants. However, de novo domestication via genome editing is a quick approach to produce rice with high yields from orphans or wild relatives. African wild rice, Oryza longistaminata, which is part of the AA-genome Oryza species has two types of propagation strategies viz. vegetative propagation via rhizome and seed propagation. It also shows tolerance to multiple types of abiotic stress, and therefore O. longistaminata is considered a key candidate of wild rice for heat, drought, and salinity tolerance, and it is also resistant to lodging. Importantly, O. longistaminata is perennial and propagates also via rhizomes both of which are traits that are highly valuable for the sustainable production of rice. Therefore, O. longistaminata may be a good candidate for de novo domestication through genome editing to obtain rice that is more climate resilient than modern elite cultivars of O. sativa.

An endoplasmic reticulum-associated degradation-related E2-E3 enzyme pair controls grain size and weight through the brassinosteroid signaling pathway in rice

Grain size is an important agronomic trait, but our knowledge about grain size determination in crops is still limited. Endoplasmic reticulum (ER)-associated degradation (ERAD) is a special ubiquitin proteasome system that is involved in degrading misfolded or incompletely folded proteins in the ER. Here, we report that SMALL GRAIN 3 (SMG3) and DECREASED GRAIN SIZE 1 (DGS1), an ERAD-related E2-E3 enzyme pair, regulate grain size and weight through the brassinosteroid (BR) signaling pathway in rice (Oryza sativa). SMG3 encodes a homolog of Arabidopsis (Arabidopsis thaliana) UBIQUITIN CONJUGATING ENZYME 32, which is a conserved ERAD-associated E2 ubiquitin conjugating enzyme. SMG3 interacts with another grain size regulator, DGS1. Loss of function of SMG3 or DGS1 results in small grains, while overexpression of SMG3 or DGS1 leads to long grains. Further analyses showed that DGS1 is an active E3 ubiquitin ligase and colocates with SMG3 in the ER. SMG3 and DGS1 are involved in BR signaling. DGS1 ubiquitinates the BR receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1) and affects its accumulation. Genetic analysis suggests that SMG3, DGS1, and BRI1 act together to regulate grain size and weight. In summary, our findings identify an ERAD-related E2-E3 pair that regulates grain size and weight, which gives insight into the function of ERAD in grain size control and BR signaling.

Genetic Localization and Homologous Genes Mining for Barley Grain Size

Grain size is an important agronomic trait determining barley yield and quality. An increasing number of QTLs (quantitative trait loci) for grain size have been reported due to the improvement in genome sequencing and mapping. Elucidating the molecular mechanisms underpinning barley grain size is vital for producing elite cultivars and accelerating breeding processes. In this review, we summarize the achievements in the molecular mapping of barley grain size over the past two decades, highlighting the results of QTL linkage analysis and genome-wide association studies. We discuss the QTL hotspots and predict candidate genes in detail. Moreover, reported homologs that determine the seed size clustered into several signaling pathways in model plants are also listed, providing the theoretical basis for mining genetic resources and regulatory networks of barley grain size.

Auxin regulation on crop: from mechanisms to opportunities in soybean breeding

Breeding crop varieties with high yield and ideal plant architecture is a desirable goal of agricultural science. The success of "Green Revolution" in cereal crops provides opportunities to incorporate phytohormones in crop breeding. Auxin is a critical phytohormone to determine nearly all the aspects of plant development. Despite the current knowledge regarding auxin biosynthesis, auxin transport and auxin signaling have been well characterized in model Arabidopsis (Arabidopsis thaliana) plants, how auxin regulates crop architecture is far from being understood, and the introduction of auxin biology in crop breeding stays in the theoretical stage. Here, we give an overview on molecular mechanisms of auxin biology in Arabidopsis, and mainly summarize auxin contributions for crop plant development. Furthermore, we propose potential opportunities to integrate auxin biology in soybean (Glycine max) breeding.

A chromosome-level genome assembly of an early matured aromatic Japonica rice variety Qigeng10 to accelerate rice breeding for high grain quality in Northeast China

Early-matured aromatic japonica rice from the Northeast is the most popular rice commodity in the Chinese market. The Qigeng10 (QG10) was one of the varieties with the largest planting area in this region in recent years. It was an early-matured japonica rice variety with a lot of superior traits such as semi-dwarf, lodging resistance, long grain, aromatic and good quality. Therefore, a high-quality assembly of Qigeng10 genome is critical and useful for japonica research and breeding. In this study, we produced a high-precision QG10 chromosome-level genome by using a combination of Nanopore and Hi-C platforms. Finally, we assembled the QG10 genome into 77 contigs with an N50 length of 11.80 Mb in 27 scaffolds with an N50 length of 30.55 Mb. The assembled genome size was 378.31Mb with 65 contigs and constituted approximately 99.59% of the 12 chromosomes. We identified a total of 1,080,819 SNPs and 682,392 InDels between QG10 and Nipponbare. We also annotated 57,599 genes by the Ab initio method, homology-based technique, and RNA-seq. Based on the assembled genome sequence, we detected the sequence variation in a total of 63 cloned genes involved in grain yield, grain size, disease tolerance, lodging resistance, fragrance, and many other important traits. Finally, we identified five elite alleles (qTGW2^Nipponbare , qTGW3^Nanyangzhan , GW5^IR24 , GW6^Suyunuo , and qGW8^Basmati385 ) controlling long grain size, four elite alleles (COLD1^Nipponbare , bZIP73^Nipponbare , CTB4a^{Kunmingxiaobaigu} , and CTB2^{Kunmingxiaobaigu} ) controlling cold tolerance, three non-functional alleles (DTH7^Kitaake , Ghd7^Hejiang19 , and Hd1^Longgeng31 ) for early heading, two resistant alleles (Pia^Akihikari and Pid4^Digu ) for rice blast, a resistant allele STV11^Kasalath for rice stripe virus, an NRT1.1B^IR24 allele for higher nitrate absorption activity, an elite allele SCM3^Chugoku117 for stronger culms, and the typical aromatic gene badh2-E2 for fragrance in QG10. These results not only help us to better elucidate the genetic mechanisms underlying excellent agronomic traits in QG10 but also have wide-ranging implications for genomics-assisted breeding in early-matured fragrant japonica rice.

Molecular bases of rice grain size and quality for optimized productivity

The accomplishment of further optimization of crop productivity in grain yield and quality is a great challenge. Grain size is one of the crucial determinants of rice yield and quality; all of these traits are typical quantitative traits controlled by multiple genes. Research advances have revealed several molecular and developmental pathways that govern these traits of agronomical importance. This review provides a comprehensive summary of these pathways, including those mediated by G-protein, the ubiquitin-proteasome system, mitogen-activated protein kinase, phytohormone, transcriptional regulators, and storage product biosynthesis and accumulation. We also generalize the excellent precedents for rice variety improvement of grain size and quality, which utilize newly developed gene editing and conventional gene pyramiding capabilities. In addition, we discuss the rational and accurate breeding strategies, with the aim of better applying molecular design to breed high-yield and superior-quality varieties.