Fruit lignification is due to lignin deposition in the cell wall during cell development. However, there are few studies on the regulation of cell wall lignification and lignin biosynthesis during fruit pigmentation. In this study, we investigated the regulation of cell wall lignification and lignin biosynthesis during pigmentation of winter jujube. The cellulose content decreased, while the lignin content increased in the winter jujube pericarp during pigmentation. Safranin O-fast green staining showed that the cellulose content was higher in the cell wall of winter jujube prior to pigmentation, whereas the lignin in the cell wall increased after pigmentation. The thickness of the epidermal cells decreased with pericarp pigmentation. A combined metabolomics and transcriptomics analysis showed that guaiacyl-syringyl (G-S) lignin was the main lignin type in the pericarp of winter jujube, and F5H (LOC107424406) and CCR (LOC107420974) were preliminarily identified as the key genes modulating lignin biosynthesis in winter jujube. Seventeen MYB and six NAC transcription factors (TFs) with potential regulation of lignin biosynthesis were screened out based on phylogenetic analysis. Three MYB and two NAC TFs were selected as candidate genes and further studied in detail. Arabidopsis ectopic expression and winter jujube pericarp injection of the candidate genes indicated that the MYB activator (LOC107425254) and the MYB repressor (LOC107415078) control lignin biosynthesis by regulating CCR and F5H, while the NAC (LOC107435239) TF promotes F5H expression and positively regulates lignin biosynthesis. These findings revealed the lignin biosynthetic pathway and associated genes during pigmentation of winter jujube pericarp and provide a basis for further research on lignin regulation.

中文翻译：

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冬枣色素沉着过程中细胞壁木质化和木质素生物合成的调控

果实木质化是由于细胞发育过程中木质素沉积在细胞壁上。然而，关于果实色素沉着过程中细胞壁木质化和木质素生物合成调控的研究较少。在这项研究中，我们研究了冬枣色素沉着过程中细胞壁木质化和木质素生物合成的调控。冬枣果皮在色素沉着过程中纤维素含量降低，木质素含量升高。Safranin O-fast green染色显示，冬枣色素沉着前细胞壁中纤维素含量较高，而色素沉着后细胞壁中木质素含量增加。表皮细胞的厚度随着果皮色素沉着而减少。F5H(LOC107424406） 和CCR(LOC107420974) 被初步确定为冬枣木质素生物合成调控的关键基因。基于系统发育分析，筛选出 17 个 MYB 和 6 个 NAC 转录因子（TFs）具有潜在的木质素生物合成调节作用。选择三个 MYB 和两个 NAC TF 作为候选基因并进一步详细研究。拟南芥候选基因的异位表达和冬枣果皮注射表明MYB激活剂（LOC107425254) 和 MYB 阻遏物 (LOC107415078) 通过调节来控制木质素的生物合成CCR和F5H, 而 NAC (LOC107435239) TF 提升F5H表达并正向调节木质素的生物合成。这些发现揭示了冬枣果皮色素沉着过程中木质素生物合成途径及相关基因，为进一步研究木质素调控提供了依据。