Abstract Postharvest granulation is a serious physiological disorder during storage in navel orange fruit, while the molecular basis remains largely unknown. Orange fruit exhibited obvious gradient of total soluble solids, which gradually increased from stem to stylar region, and granulation occurrence often initiated at the stem and extended towards the rest. Here, we performed systematical analysis of metabolites, coding transcriptome, lncRNAs and single-base resolution methylome in juice sacs during granulation. Through a comparison of RNA-Seq data generated from stem and mid juice sacs of either normal or incipient granulated fruit, 6022 genes were reliably identified to be differentially expressed upon granulation, which uncovers various metabolic pathway underlying the decreasing of sugars and organic acids, and increasing of cell wall components. Further, 486 lncRNAs were differentially expressed in granulated juice sacs, predicted to regulate cell wall metabolism. Genome wide analysis of fruit methylome during granulation indicated that DNA methylation might be unlikely involved in granulation process. A serial of transcription factors, including homolog of E2Fc and UPB1, potentially play crucial roles in granulation process, mainly via regulating the secondary cell wall synthesis. It is the first study to unravel the molecular mechanism underlying postharvest granulation in sweet orange fruit.

中文翻译：

---

通过代谢物、转录组和甲基化组分析揭示橙子果实采后造粒的分子基础

摘要 脐橙果实采后成粒是脐橙果实贮藏过程中一种严重的生理障碍，其分子基础尚不清楚。橙果实总可溶性固形物呈明显梯度，从茎到花柱区逐渐增加，肉芽的发生多从茎部开始，向其余部分扩展。在这里，我们对造粒过程中汁囊中的代谢物、编码转录组、lncRNA 和单碱基分辨率甲基化组进行了系统分析。通过比较正常或初期颗粒状果实的茎和中部汁囊产生的 RNA-Seq 数据，可靠地鉴定了 6022 个基因在颗粒形成时差异表达，揭示了糖和有机酸减少的各种代谢途径，和细胞壁成分的增加。此外，486 个 lncRNA 在颗粒状汁囊中差异表达，预计可调节细胞壁代谢。造粒过程中水果甲基化组的全基因组分析表明 DNA 甲基化可能不太可能参与造粒过程。一系列转录因子，包括 E2Fc 和 UPB1 的同源物，可能在造粒过程中发挥关键作用，主要是通过调节次生细胞壁的合成。这是首次揭示甜橙果实采后造粒的分子机制的研究。造粒过程中水果甲基化组的全基因组分析表明 DNA 甲基化可能不太可能参与造粒过程。一系列转录因子，包括 E2Fc 和 UPB1 的同源物，可能在造粒过程中发挥关键作用，主要是通过调节次生细胞壁的合成。这是首次揭示甜橙果实采后造粒的分子机制。造粒过程中水果甲基化组的全基因组分析表明 DNA 甲基化可能不太可能参与造粒过程。一系列转录因子，包括 E2Fc 和 UPB1 的同源物，可能在造粒过程中发挥关键作用，主要是通过调节次生细胞壁的合成。这是首次揭示甜橙果实采后造粒的分子机制。