Walnuts (including those covered with a pellicle) are loved for their rich nutritional value. And the popular varieties of walnut cultivation are Juglans sigillata L. The pellicle (seed coat) of these walnut cultivars has different colors and has an indispensable influence on the walnut quality formation. However, there are few reports on the pellicle color and quality formation in different developmental stages of walnut (Juglans sigillata L.). Therefore, in this study, three walnut cultivars (F, Q, and T) with different pellicle colors were selected for transcriptome sequencing and physiological index analysis of the color and quality formation mechanisms at different development stages. The results showed that with the development of walnut fruit, the starch sucrose metabolism pathway in the pellicle was activated and promoted starch hydrolysis. Meanwhile, the expression levels of genes related to the alpha-linolenic acid metabolism pathway were significantly increased during walnut maturation, especially in F2. Some physiological indicators related to lipid oxidation were also detected and analyzed in this study, such as MDA, CAT, POD and DPPH. These results were similar to the expression patterns of corresponding regulatory genes in the RNA-Seq profile. In addition, lignin synthesis genes were up-regulated in the phenylpropanoid metabolic pathway, while key genes enriched in the flavonoid and anthocyanin synthesis pathways were down-regulated. The results were consistent with the results of total anthocyanins and flavonoid content detection during walnut development. Therefore, this experiment suggested that with the maturation of walnut pellicle, the gene expression in the phenylpropanoid metabolic pathway flowed to the branch of lignin synthesis, especially in the Q variety, resulting in lower flavonoid and anthocyanin content at the maturity stage than immature. This is also the main reason for the pale pellicle of the three walnut varieties after mature. The findings of this study showed that changes in the expression levels of regulating genes for lipid, starch, sugar, and flavonoid synthesis during walnut development influenced the accumulation of the related metabolite for walnut quality formation and pellicle color. The results of this experiment provided the molecular basis and reference for the breeding of high nutritional quality walnut varieties.

核桃（包括覆有薄膜的核桃）因其丰富的营养价值而备受喜爱。而核桃栽培的热门品种是Juglans sigillata L。这些核桃品种的表皮（种皮）颜色各异，对核桃品质的形成有着不可或缺的影响。然而，关于核桃（ Juglans sigillata）不同发育阶段的表膜颜色和品质形成的报道较少。L.)。因此，本研究选择了3个核桃品种（F、Q、T），分别对核桃不同发育阶段的颜色和品质形成机制进行转录组测序和生理指标分析。结果表明，随着核桃果实的发育，表膜中的淀粉蔗糖代谢途径被激活，促进了淀粉水解。同时，在核桃成熟过程中，α-亚麻酸代谢途径相关基因的表达水平显着增加，尤其是在F2。本研究还检测和分析了一些与脂质氧化有关的生理指标，如MDA、CAT、POD和DPPH。这些结果与 RNA-Seq 谱中相应调控基因的表达模式相似。此外，木质素合成基因在苯丙素代谢途径中上调，而富含黄酮和花青素合成途径的关键基因被下调。结果与核桃发育过程中总花青素和黄酮含量检测结果一致。因此，本实验提示，随着核桃皮膜的成熟，苯丙烷代谢途径中的基因表达流向木质素合成分支，特别是在Q品种中，导致成熟期黄酮类和花青素含量低于未成熟期。这也是三个核桃品种成熟后表皮苍白的主要原因。本研究结果表明，脂质、淀粉、糖、核桃发育过程中类黄酮的合成影响了核桃品质形成和表皮颜色相关代谢物的积累。本试验结果为选育高营养优质核桃品种提供了分子基础和参考。