Ugwuanyi Samson, Makhoul Manar, Golicz Agnieszka A, Obermeier Christian, Snowdon Rod J
Department of Plant Breeding, Justus Liebig University, Giessen, Germany.
Front Plant Sci. 2025 Jun 13;16:1565210. doi: 10.3389/fpls.2025.1565210. eCollection 2025.
Faba bean is a valuable legume crop desired globally for its high nutritional composition. However, the seed vicine and convicine (v-c) content reduces the nutritional quality of faba bean protein and can induce favism in susceptible individuals. Recently, gene, encoding a bi-functional riboflavin protein, was reported to initiate the v-c biosynthetic pathway in . In low v-c cultivars, a 2 bp insertion in this gene disrupts its function by causing a frameshift and premature stop codon. However, because v-c biosynthesis is only partially reduced, this suggests that additional genes may also be involved in the pathway. Here, we identify and investigate multiple tandem gene duplications at the locus. Our findings reveal that exhibits multiple structural variants and copy number variations, but its expression is independent of copy number. Low v-c genotypes carry both variants of the gene - with and without the 2 bp insertion - but only the variant with the insertion is expressed. In contrast, high v-c genotypes consistently express the variant lacking the insertion. Although some high v-c genotypes also carry the insertion, it is found in a non-expressed variant, while the expressed variant lacks the insertion, resulting in the high v-c phenotype. We also report a novel diverging homolog, , which shares expression domains with . This homologous gene encodes GTP cyclohydrolase II, a critical enzyme in the v-c pathway. Expression of this gene contributes ~5-10% of riboflavin gene transcripts in immature seeds suggesting it as a minor-effect candidate locus in v-c biosynthesis. Moreover, two SNPs within the coding sequence of segregated with v-c content, offering a reliable alternative for marker-assisted selection in faba bean breeding. In conclusion, this study contributes to the elucidation of the complex genetic regulation of v-c biosynthesis and provides valuable insights to facilitate further efforts in its reduction in faba bean.
蚕豆是一种因高营养成分而在全球备受青睐的重要豆类作物。然而，种子中的蚕豆嘧啶和伴蚕豆嘧啶（v-c）含量会降低蚕豆蛋白的营养品质，并可能在易感个体中引发蚕豆病。最近，有报道称编码一种双功能核黄素蛋白的基因启动了蚕豆中v-c的生物合成途径。在低v-c品种中，该基因中的一个2bp插入通过导致移码和过早的终止密码子破坏了其功能。然而，由于v-c生物合成仅部分减少，这表明该途径可能还涉及其他基因。在此，我们鉴定并研究了该位点的多个串联基因重复。我们的研究结果表明该基因呈现出多种结构变异和拷贝数变异，但其表达与拷贝数无关。低v-c基因型携带该基因的两种变体——有和没有2bp插入的——但只有带有插入的变体表达。相比之下，高v-c基因型始终表达缺乏插入的变体。尽管一些高v-c基因型也携带插入，但它存在于一个不表达的变体中，而表达的变体缺乏插入，从而导致高v-c表型。我们还报道了一个新的分化同源基因，它与该基因共享表达域。这个同源基因编码GTP环化水解酶II，这是v-c途径中的一种关键酶。该基因的表达在未成熟种子的核黄素基因转录本中占约5-10%，表明它是v-c生物合成中的一个微效候选位点。此外，该基因编码序列内的两个单核苷酸多态性（SNP）与v-c含量分离，为蚕豆育种中的标记辅助选择提供了可靠的替代方法。总之，本研究有助于阐明v-c生物合成的复杂遗传调控，并为促进蚕豆中v-c含量降低的进一步研究提供了有价值的见解。
