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.

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 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.

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.

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.

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.