Antioxidants · 5 authors, 2 centres
This summary was generated by AI from a single paper. It has not been reviewed by a clinician and is not clinical advice. Verify against the source before acting on it.
This study analyzed genetic variations in the γ-TMT gene across 475 rice accessions, identifying 27 haplotypes and two functional SNPs that significantly affect vitamin E isomer levels. The findings provide valuable markers for breeding rice with enhanced nutritional quality, particularly for increasing α-tocopherol content.
**Background:** Vitamin E, comprising tocopherols and tocotrienols, is a crucial lipid-soluble antioxidant for human health, with α-tocopherol being the most bioactive form. Rice (Oryza sativa L.) is a staple food for half the world's population and contains vitamin E isoforms, but levels vary among cultivars. The γ-tocopherol methyltransferase (γ-TMT) gene encodes a key enzyme that converts γ-tocochromanols to α-tocochromanols, making it a target for improving vitamin E content. This study aimed to characterize genetic diversity, haplotypes, and evolutionary dynamics of the γ-TMT gene in a Korean rice collection (KRICE) of 475 accessions, and to assess the impact of haplotypes on tocochromanol accumulation.
**Methods:** The study utilized whole-genome resequencing data (average 15× coverage) from 475 rice accessions, including 421 cultivated and 54 wild accessions, categorized into six ecotypes: temperate japonica (n=279), tropical japonica (n=26), indica (n=102), aus (n=9), aromatic (n=2), admixture (n=3), and wild (n=54). Variant calling was performed using GATK, filtering for minor allele frequency ≥0.05 and maximum missing data ≤0.2. Population structure was assessed using fastStructure (K=2 to 7) and principal component analysis (PCA). Nucleotide diversity (π), Tajima's D, and fixation index (FST) were calculated with a 500 bp sliding window. Haplotype analysis was conducted using DnaSP and PopART. For phenotypic analysis, tocochromanol isomers (α-tocopherol, γ-tocopherol, α-tocotrienol, γ-tocotrienol) were quantified by gas chromatography (GC) in 240 selected accessions representing five major haplotypes (Hap_1, Hap_2, Hap_19, Hap_20, Hap_21). Statistical differences were assessed using Student's t-test.
**Key Results:** A total of 177 polymorphic sites were identified in the γ-TMT gene region, including 138 SNPs and 39 InDels, with 122 in introns, 44 in exons, and 11 in the 3'UTR. The highest genetic diversity was observed in wild rice. Population structure analysis at K=3 separated indica and japonica groups, with wild accessions showing admixture patterns. PCA revealed three clusters: Cluster A included all japonica, wild, aromatic, and some indica; Cluster B comprised aus and indica; Cluster C was exclusively indica. FST values indicated high differentiation between temperate japonica and indica (0.7120) and between temperate japonica and aus (0.8357), while low differentiation was observed between admixture and aromatic (FST=0) and wild and aromatic (FST=0). Nucleotide diversity (π) was highest in indica (mean π=0.0060), followed by wild (π=0.0045), tropical japonica (π=0.0015), and temperate japonica (π=0.0009). Tajima's D was positive for indica (mean 0.6293, maximum 2.09848 at position 28,897,500), indicating balancing selection or population contraction, while negative values for japonica and wild groups suggested recent expansion or positive selection. Twenty-seven haplotypes were identified; Hap_1 (reference sequence) was the most prevalent (278 accessions, mainly temperate japonica). Two functional SNPs (fSNPs) in exons—tmt-E2-28,895,665-G/A (valine to isoleucine) and tmt-E4-28,896,689-A/G (arginine to glycine)—were found in 93 accessions (87 indica, 4 aus, 2 admixture). Phenotypic analysis showed that Hap_1 had significantly higher α-tocopherol (AT), α-tocotrienol (AT3), and total tocopherol (TT) compared to Hap_19, Hap_20, and Hap_21 (p<0.0001 to p<0.05), while γ-tocopherol (GT) and γ-tocotrienol (GT3) were lower. Hap_2, characterized by a 3'UTR SNP (tmt-3UTR-28,897,360-T/A), also showed higher AT, AT3, and TT than Hap_19-21. In japonica, Hap_2 had significantly lower AT, AT3, TT, and total vitamin E but higher GT compared to Hap_1. In indica, haplotypes Hap_19-21 showed lower AT and AT3 but higher GT and GT3, with no significant differences among them for total tocopherol or tocotrienol.
**Clinical Implications:** This study provides a comprehensive genetic analysis of the γ-TMT gene in rice, identifying key haplotypes and functional SNPs that significantly influence vitamin E profiles. The findings offer molecular markers for breeding programs aimed at enhancing α-tocopherol content, the most bioactive form of vitamin E, which is associated with reduced risk of inflammatory diseases, cardiovascular disease, Alzheimer's, cancer, and cataracts. By selecting haplotypes such as Hap_1 or Hap_2, breeders can develop rice varieties with improved nutritional quality, potentially addressing vitamin E deficiency in populations that rely heavily on rice as a dietary staple. The study also highlights the importance of 3'UTR variations in modulating gene expression and tocochromanol accumulation, providing targets for genetic engineering.