Transcriptomic and physiological analysis identifies a gene network module highly associated with brassinosteroid regulation in hybrid sweetgum tissues differing in the capability of somatic embryogenesis

第一作者：Ruirui Zhao

第一单位：北京林业大学

第一通讯：Lisheng Kong

Abstarct

背景回顾：Somatic embryogenesis is a preferred method for large-scale production of forest trees due to its high propagation efficiency.

体细胞胚胎发生因其极高的繁殖效率，是林木大规模繁殖的首选方法。

研究材料：In this study, hybrid sweetgum leaves with phase changes from mature to embryogenic state were selected as experimental material to study somatic embryo initiation. Embryogenicity ranged from high to low, i.e. from 45%, 25%, and 12.5% to 0, with the samples of embryogenic callus (EC), whiten leaf edge (WLI), whiten leaf (WLII), and green leaf (GL) respectively.

本文中，杂交枫香具有从成熟到胚性状态这种发育转变的叶片，被用作研究体胚起始的材料。作者比较了四种材料的体胚发生能力，由高到低分别是胚性愈伤组织（EC）、变白的叶边缘（WLI）、变白的叶片（WLII）以及绿色的叶片（GL），其体胚发生效率分别是45%、25%、12.5%以及0%。

结果1-内源BRs与SE效率、SE相关基因的表达：High correlations existed between embryogenicity and endogenous brassinosteroids (BRs) (r = 0.95, p < 0.05). Similarly, concentrations of endogenous BRs of the sample set correlated positively (r = 0.93, 0.99, 0.87, 0.99, 0.96 respectively, P < 0.05) to expression of somatic embryo (SE)-related genes, i.e. BBM, LEC2, ABI3, PLT2, and WOX2.

有趣的是，作者发现这四种材料的体胚发生效率与内源的油菜素内酯（BR）的含量呈显著正相关（r 等于0.95，p小于 0.05）。同时，这些材料中的内源BR含量与BBM、LEC2、ABI3、PLT2以及WOX2等体胚发生相关基因的表达也呈显著正相关（r 分别为0.93、0.99、0.87、0.99和0.96，P 小于 0.05）。

结果2-调控网络：Hierarchical cluster and weighted gene coexpression network analysis identified modules of coexpressed genes and network in 4820 differentially expressed genes (DEGs) from All-BR-Regulated Genes (ABRG).

作者基于BR调控基因（ABRG）中的4820个差异表达基因，进行了层级聚类和基因共表达网络分析，绘制了共表达基因的模块和网络。

结果3-外源BRs处理：Moreover, exogenously-supplemented epiBR, together with 2,4-D and 6-BA, increased embryogenicity of GL-sourced callus, and expression of SE- and auxin-related genes, while brassinazole (BRZ), a BR biosynthesis inhibitor, reduced embryogenicity.

此外，通过外源添加epiBR，同时与2,4-D和6-BA一起处理，能够增强来源于GL的愈伤的体胚发生效率和体胚、生长素相关基因的表达，而BR生物合成抑制剂BRZ的处理则会降低材料的体胚发生效率。

结论：Evidences obtained in this study revealed that BRs involved in phase change of leaf explants and may function in regulating gene expression and enhancing auxin effects.

本文的研究结果显示，BR参与了叶片外植体的发育转变，可能作用于基因表达调控，增强生长素的效应。

展望：This study successfully established protocols for inducing somatic embryogenesis from leaf explants in hybrid sweetgum, which could facilitate the propagation process greatly, and provide theoretical basis for manipulating SE competence of explants in ornamental woody plants.

本文的研究成功建立了一套杂交枫香以叶片为外植体的体胚发生体系，这将极大地促进观园林树木的繁殖过程，并为调控外植体的体胚发生能力提供理论依据。