Submergence can induce anaerobic stress on germinating seedlings in direct seeded rice paddy fields, limiting the practice of direct seeding. Longer coleoptiles improves the anaerobic tolerance of rice seedlings under submerged conditions. In a search for genes that could be beneficial for developing submergence-tolerant varieties 148 non-repetitive SNP loci were detected in on a genome-wide association study (GWAS) of coleoptile length (CL), coleoptile surface area (CSA), coleoptile volume (CV), and coleoptile diameter (CD) of 591 rice accessions subjected to 4 d of anaerobic conditions. Integration of GWAS results and gene expression data identified OsEE1, an early embryogenesis-specific enolase 1 gene associated with coleoptile length (CL) in rice grown in anaerobic conditions. Disruption of OsEE1 caused reduced CL in plants seeded under anaerobic conditions, whereas CL of OE-OsEE1 overexpression lines was significantly increased compared with the wild type. Functional analysis revealed that OsEE1 affects coleoptile length by modulating the glycolysis and tricarboxylic acid cycle pathways. Transcriptome sequencing of ko-osee1-1 knock out mutants highlighted enrichment in energy and carbohydrate metabolism, glycolysis, amino acid metabolism, and hormone signal transduction. Metabolite analysis indicated decreased levels of key metabolites in the tricarboxylic acid cycle and glycolysis pathways in ko-osee1-1 mutants compared to the wild type under anaerobic conditions. Overall, these findings shed light on the role of OsEE1 in determination coleoptile length of rice seedlings under anaerobic conditions.

Potato is globally recognized as the fourth most crucial staple food crop, trailing behind wheat, rice, and maize. Cadmium (Cd), a predominant heavy-metal pollutant in agricultural soils, demonstrates high biological toxicity and mobility. Therefore, exploring the genetic and molecular mechanisms underpinning cadmium tolerance in potato is of substantial theoretical and practical significance. In this research, an F2 population composed of 170 families was established through the cross-breeding of homozygous diploid potato lines HD-5 (highly cadmium-tolerant) and M9 (cadmium-sensitive). Employing hydroponic cultivation, six traits, namely plant height (PH), root length (RL), shoot fresh weight (SFW), root fresh weight (RFW), chlorophyll content (SPAD), and nitrogen content (LNC), were measured in potato seedlings following a 9-day treatment with 40 mg·L−1 CdCl2. By utilizing the high-density genetic map of this population for QTL mapping, a total of 35 genetic loci associated with cadmium tolerance in potato seedlings were identified. Notably, loci21 and loci22 on chromosome 9, loci29 on chromosome 10, and loci31 and loci33 on chromosome 12 were consistently detected across multiple environmental conditions. This reproducibility across environments suggests the phenotypic stability of these five loci, which are thus considered reliable and robust genetic determinants. In addition, transcriptome sequencing analysis of roots from parental lines HD-5 and M9 after cadmium treatment revealed that significantly differentially expressed genes between the two parents were associated with glutathione metabolism and photosynthesis. By integrating QTL mapping, transcriptome analysis, and gene annotation, we screened four candidate genes involved in cadmium tolerance regulation: DM8C09G01000 (GST), DM8C09G01060 (GST), DM8C09G02130 (OXP1), and DM8C06G22960 (PsaH). These findings provide molecular targets and a genetic basis for molecular breeding of cadmium-tolerant potato varieties.

Direct seeding of rice is a lightweight and simple cultivation method, which can effectively promote rice production. Anaerobic germination tolerance is one of the main traits of rice adaptability to direct seeding. The mining of related genetic loci, analysis of anaerobic traits and screening of tolerance genes provided valuable genetic resources for improving the anaerobic germination ability of direct seeding rice. This study conducted a dynamic genome-wide association study (GWAS) based on coleoptile-related traits of 591 rice natural populations, and a total of 317 SNP sites were detected. Integrated dynamic widely targeted metabolomics analysis, we found that xanthine, l -alanine and GABA may be key biomarkers that are sensitive and respond strongly to hypoxic stress perception. By WGCNA analysis of targeted metabolomics and transcriptomics, a total of 3 modules were obtained that were significantly correlated with the above three marker metabolites, namely dark green, dark gray and light green modules, respectively, and several key structural genes of OsAlaAT1 , OsGAD4 , OsAAH and Os09g0424600 that may affect hypoxic germination were screened from the 3 modules. Among them, OsAlaAT1 ( Os10g0390500 ), located in Chr10-12877840, which is within the GWAS location range of CVAN3d, is considered to be a more reliable candidate gene. Overall, in addition to providing new insight into the metabolic regulation of l -alanine, GABA and xanthine during hypoxic germination of rice. This study also provided a reference for the basic theoretical research and breeding application research on the related traits of anaerobic germination in direct-seeding rice.

A novel QTL, qCIR9.1 , that controls callus induction rate in anther culture was identified on chromosome 9 in rice, and based on RNA-seq data, Os09g0551600 was the most promising candidate gene. Anther culture, a doubled haploid (DH) technique, has become an important technology in many plant-breeding programmes. Although anther culturability is the key factor in this technique, its genetic mechanisms in rice remain poorly understood. In this study, we mapped quantitative trait loci (QTLs) responsible for anther culturability by using 192 recombinant inbred lines (RILs) derived from YZX (Oryza sativa ssp. indica) × 02428 (Oryza sativa ssp. japonica) and a high-density bin map. A total of eight QTLs for anther culturability were detected in three environments. Among these QTLs, a novel major QTL for callus induction rate (CIR) named qCIR9.1 was repeatedly mapped to a ~ 100 kb genomic interval on chromosome 9 and explained 8.39–14.14% of the phenotypic variation. Additionally, RNA sequencing (RNA-seq) was performed for the parents (YZX and 02428), low- (L-Pool) and high-CIR RILs (H-Pool) after 16 and 26 days of culture. By using the RNA of the bulked RILs for background normalization, the number of differentially expressed genes (DEGs) both between the parents and between the bulked RILs after 26 days of culture was drastically reduced to only 78. Among these DEGs, only one gene, Os09g0551600, encoding a high-mobility group (HMG) protein, was located in the candidate region of qCIR9.1. qRT-PCR analysis of Os09g0551600 showed the same results as RNA-seq, and the expression of this gene was decreased in the low-callus-induction parent (YZX) and L-Pool. Our results provide a foundational step for further cloning of qCIR9.1 and will be very useful for improving anther culturability in rice.

Background: In Asian rice production, an increasing number of countries now choose the direct seeding mode because of rising costs, labour shortages and water shortages. The ability of rice seeds to undergo anaerobic germination (AG) plays an important role in the success of direct seeding.Results: In this study, we used 2,123,725 single nucleotide polymorphism (SNP) markers based on resequencing to conduct a dynamic genome-wide association study (GWAS) of coleoptile length (CL) and coleoptile diameter (CD) in 209 natural rice populations. A total of 26 SNP loci were detected in these two phenotypes, of which 5 overlapped with previously reported loci (S1_ 39674301, S6_ 20797781, S7_ 18722403, S8_ 9946213, S11_ 19165397), and two sites were detected repeatedly at different time points (S3_ 24689629 and S5_ 27918754). We suggest that these 7 loci (−log10 (P) value > 7.3271) are the key sites that affect AG tolerance. To screen the candidate genes more effectively, we sequenced the transcriptome of the flooding-tolerant variety R151 in six key stages, including anaerobic (AN) and the oxygen conversion point (AN-A), and obtained high-quality differential expression profiles. Four reliable candidate genes were identified: Os01g0911700 (OsVP1), Os05g0560900 (OsGA2ox8), Os05g0562200 (OsDi19-1) and Os06g0548200. Then qRT-PCR and LC-MS/ MS targeting metabolite detection technology were used to further verify that the up-regulated expression of these four candidate genes was closely related to AG.Conclusion: The four novel candidate genes were associated with gibberellin (GA) and abscisic acid (ABA) regulation and cell wall metabolism under oxygen-deficiency conditions and promoted coleoptile elongation while avoiding adverse effects, allowing the coleoptile to obtain oxygen, escape the low-oxygen environment and germinate rapidly. The results of this study improve our understanding of the genetic basis of AG in rice seeds, which is conducive to the selection of flooding-tolerant varieties suitable for direct seeding.

Low temperature at the germination stage is one of the major abiotic stresses limiting rice (Oryza sativa L.) production, especially in regions where rice seeds are sown directly. However, few relevant genetic loci and genes have been identified. In this study, we report the phenotypic analysis of low temperature germination (LTG) in 200 indica rice varieties and a genome-wide association study (GWAS) of LTG in this collection using 161,657 high-quality SNPs, which were identified via genotyping-by-sequencing (GBS) of all the rice varieties. A total of 159 genetic loci were detected, and they were evenly distributed on all 12 chromosomes. Among them, 51 loci were detected more than twice; in particular, 23 loci were detected repeatedly in both the wet and dry seasons, and 569 genes were predicted in the 200-kb genomic region harbouring these 23 loci. Furthermore, 14,742 differentially expressed genes (DEGs) were identified using RNA sequencing. By integrating GWAS and RNA sequencing, 179 candidate DEGs were obtained. Sequence variation in the region of loci 95 was analyzed using 20 varieties with extreme phenotype. The polymorphisms of three DEGs (Os07g0585500, Os07g0585700, Os07g0585900) were associated with their phenotypes. Haplotype analysis of the three genes demonstrated that almost all the varieties with the same haplotype as japonica Nipponbare on the three DEGs showed high LTG ability. These findings provide valuable information for understanding the genetic control of LTG and performing molecular breeding with marker-assisted selection in indica rice.

Background Seed germination and young seedling growth are important agricultural traits for developing populations of both irrigated and directly seeded rice. Previous studies have focused on the identification of QTLs. However, there are few studies on the metabolome or transcriptome of germination and young seedling growth in rice. Results Here, an indica rice and a japonica rice were used as materials, and the transcripts and metabolites were detected during the germination and young seedling growth periods on a large scale by using RNA sequencing and a widely targeted metabolomics method, respectively. Fourteen shared transcripts and 15 shared metabolites that were continuously differentially expressed in the two materials were identified and may be essential for seed germination and young seedling growth. Enrichment analysis of differentially expressed genes in transcriptome expression profiles at different stages indicated that cell wall metabolism, lipid metabolism, nucleotide degradation, amino acid, etc., were enriched at 0–2 days, and most of the results are consistent with those of previous reports. Specifically, phenylpropanoid biosynthesis and glutathione metabolism were continuously enriched during the seed germination and young seedling growth stages. Next, KO enrichment analysis was conducted by using the differentially expressed genes of the two materials at 2, 3 and 4 days. Fourteen pathways were enriched. Additionally, 44 differentially expressed metabolites at 2, 3 and 4 days were identified. These metabolites may be responsible for the differences in germination and young seedling growth between the two materials. Further attention was focused on the ascorbate–glutathione pathway, and it was found that differences in ROS-scavenging abilities mediated by some APX, GPX and GST genes may be directly involved in mediating differences in the germination and young seedling growth speed of the two materials. Conclusions In summary, these results may enhance the understanding of the overall mechanism of seed germination and young seedling growth, and the outcome of this study is expected to facilitate rice breeding for direct seeding.

The metabolic profile of rice (Oryza sativa) during germination under low temperature (LT) has not been reported. In this study, the rice varieties 02428 (japonica) and YZX (indica) were subjected to experiments consisting of treatments including LT, normal temperature (NT) and a transition from LT to NT, and tissues were sampled at different time points during germination. A total of 730 metabolites were detected by a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based widely targeted metabolomics method. On the basis of the screening criteria of increased contents under LT and decreased contents under NT, we identified 35 different metabolites that responded to LT stress among the 730 metabolites. Furthermore, the content differences of the 35 metabolites were compared when the samples were transferred from LT to NT. According to a fold change <0.5 or a variable importance in projection (VIP) score>1 at the transition point, 7 out of the 35 metabolites responded significantly to LT stress and were defined as key metabolites. A partial least squares (PLS) regression model of seven key metabolites with seedling length (SL), seedling area (SSA), and seedling volume (SV) was constructed, and the fitting effect was good. These seven key metabolites participate in the biosynthesis of amino acids and phenylpropanoids and in the metabolism of glutathione and inositol phosphate. This study laid a foundation for an improved understanding of the LT-germination mechanism of rice seeds.

Seed germination and early seedling growth are important agricultural traits for developing populations of both irrigated and directly seeded rice (DSR). To investigate the genetic mechanisms underlying seed germination and early seedling growth in rice, 275 recombinant inbred lines (RILs) were genotyped in this study via the genotyping-by-sequencing (GBS) approach to construct a high-density linkage bin map based on the parent-independent genotyping method. Quantitative trait loci (QTLs) for 12 traits related to seed germination and early seedling growth were analyzed. Totally, 22 additive loci were detected, after analysis of the interaction between additive QTLs and environments, five stable additive loci were obtained. Among them, loci 4, 5, 12 and 14 exhibited clear pleiotropic effects that were associated with multiple traits. Analysis of the effects of the five additive stable loci showed that a single locus increased the corresponding phenotypic value. Ten of the 275 RILs pyramided the excellent alleles of the five stable genetic loci. Most phenotypic values of the ten RILs were greater than the average values. Four RILs (G260, G342, G371, and G401) with more excellent phenotypic values were subsequently selected; these RILs could serve as donor parents of favorable alleles in the breeding process. Due to the existence of pleiotropy, the use of these genetic loci for pyramid breeding can further increase the efficiency to reach breeding goals. In addition, these five stable loci have an average physical interval of only 170 kb, we also further identified five promising candidate genes by qRT-PCR, which provides us with a basis for future cloning of these genes. Overall, this work will help broaden our understanding of the genetic control of seed germination and early seedling growth, and this study provides both a good theoretical basis and a new genetic resource for the breeding of direct-seeded rice.