Unraveling Site-Specific Seed Formation Abnormalities in Picea Neoveitchii Mast. Trees via Widely Metabolomic and Transcriptomic Analysis

Background: Picea neoveitchii Mast. is a rare and threatened species of evergreen coniferous tree in China. Damaged seeds, abnormal seed growth, and empty seed shells are common problems in P. neoveitchii in China. But the intensity of these abnormalities varies at different places; unfortunately, the reasons behind these inconsistencies are completely unknown.Results: In this study, we compared the seeds from two locations: Taibai (Shaanxi province), a 150-year-old tree (TB150), and Zhouqu (Gansu province), a 150-year-old tree (ZQ150). The results showed obvious changes in 43 different metabolites. Among them, the number of damaged seeds and empty seed shells was higher in TB150, and the number of abnormal and normal (viable) seeds was higher in ZQ150 by increasing indole-3-acetic acid (IAA), methyl jasmonate (JA-me), and brassinosteroid (BR) contents and decreasing abscisic acid (ABA) contents. Moreover, to further investigate these inconsistencies, we used high-throughput deep sequencing technology, aiming to perform de novo transcriptomic assembly and functional annotation of unigenes at both sites. Totally, 2355 differentially expressed genes were observed between TB150 and ZQ150, with 1280 upregulated and 1075 downregulated. Hormone signaling and sugar metabolism-related unigenes were further studied for their involvement in these inconsistencies.Summary: ZQ150 increased the number of normal seeds by enhancing endogenous IAA levels and the expression of genes related to the auxin signaling pathway. In contrast, TB150 had the highest percentage of empty seed shells, which can be attributed to higher ABA levels and the activation of genes involved in the ABA signaling pathway. We also hypothesize that the upregulation of genes related to sugar metabolism promotes normal seed development.

背景：秦岭云杉（Picea neoveitchii Mast.）是中国特有的珍稀濒危常绿针叶树种。种子破损、胚发育异常以及空瘪种壳是我国秦岭云杉普遍存在的问题，但这类异常的发生程度在不同分布地存在显著差异，而造成这种差异的具体机制目前仍完全未知。
结果：本研究选取两个分布地的植株种子开展对比分析：分别为陕西太白山的150年生植株（TB150）与甘肃舟曲的150年生植株（ZQ150）。代谢组分析结果显示，两地植株的43种代谢物存在显著差异。其中TB150的破损种子与空瘪种壳占比更高，而ZQ150的异常种子与正常（有活力）种子占比更高，这与其体内吲哚-3-乙酸（indole-3-acetic acid, IAA）、茉莉酸甲酯（methyl jasmonate, JA-me）及油菜素内酯（brassinosteroid, BR）含量升高，同时脱落酸（abscisic acid, ABA）含量降低密切相关。为进一步探究两地种子表型差异的成因，本研究采用高通量深度测序技术，对两个样地的样本进行从头转录组组装与单基因簇（unigenes）功能注释。TB150与ZQ150之间共鉴定出2355个差异表达基因，其中1280个基因上调表达，1075个基因下调表达。本研究进一步针对激素信号通路与糖代谢相关的单基因簇展开分析，以明确其在两地表型差异中的作用。
总结：ZQ150可通过提升内源IAA水平以及生长素信号通路相关基因的表达，增加正常种子的占比。与之相反，TB150的空瘪种壳占比最高，这可归因于其体内较高的ABA水平以及ABA信号通路相关基因的激活。本研究同时推测，糖代谢相关基因的上调表达可促进种子正常发育。