巴西橡胶树miR396家族鉴定及乙烯应答模式分析

miR396 family identification and ethylene responses in Hevea brasiliensis

  • 摘要: 【目的】 对巴西橡胶树miR396家族成员进行鉴定,并分析其对乙烯的应答模式,为解析乙烯在橡胶树乳管细胞产排胶中的分子机制及乙烯应答相关miRNA在橡胶树胶乳代谢中的调控作用提供理论依据。【方法】 基于转录组测序数据筛选到重要响应因子miR396,并利用其成熟体序列在橡胶树基因组中鉴定出miR396家族成员,使用生物信息学方法对该家族成员的二级结构、系统发育关系、启动子区顺式作用元件进行预测分析,并通过实时荧光定量PCR检测miR396在乙烯利处理不同时间下的表达水平。【结果】 通过全基因组鉴定共获得14个巴西橡胶树miR396家族成员,分别将其成熟体序列命名为hbr-miR396a~hbr-miR396l,其中hbr-miR396bhbr-miR396k分别含有2个成熟体(hbr-miR396b-5phbr-miR396b-3p、hbr-miR396k-5phbr-miR396k-3p),这些miR396家族成员前体均能形成典型的茎环结构,不均匀分布在9条染色体上。系统发育结果显示,该家族前体序列具有遗传多样性,但同一物种中成熟体序列在进化过程中具有一定的保守性。14个miR396家族成员启动子区含有大量激素响应元件、防御和应激响应元件、光响应元件等,推测其参与激素响应、胁迫应答及发育调控。巴西橡胶树miR396家族成员中,仅hbr-miR396b-5phbr-miR396ehbr-miR396k-5p在胶乳中高表达,其中hbr-miR396ehbr-miR396k-5p随着乙烯利处理时间的延长持续上调表达,而hbr-miR396b-5p在处理后6 h下调表达后又上调表达。靶基因预测结果显示,多数靶基因在乙烯利处理过程中下调表达,与高丰度表达的巴西橡胶树miR396家族成员表达趋势相反,符合miRNA沉默机制。GO功能注释和KEGG信号通路富集分析结果显示,这些靶基因在油菜素内酯生物合成、叶片发育、果糖和甘露糖代谢等方面发挥功能。【结论】 在橡胶树割面乙烯利处理后,巴西橡胶树miR396家族成员通过复杂的多层次调控网络参与调控橡胶树的胁迫应答、胶乳合成及激素响应等关键生物学过程,对橡胶树胶乳代谢产生重要影响,其中hbr-miR396b-5phbr-miR396ehbr-miR396k-5p可能通过差异化调控机制参与橡胶树乳管乙烯应答通路。

     

    Abstract: 【Objective】 This study aimed to identify miR396 family members in Hevea brasiliensis and analyze their ethylene response patterns, thereby providing theoretical basis for elucidating the molecular mechanisms of ethylene in latex production and flow in Hevea brasiliensis laticifer cells and regulatory role of miRNAs related to ethylene response in latex metabolism of Hevea brasiliensis. 【Method】 The key response factor miR396 was identified based on transcriptomic sequencing data, and the miR396 family members were identified in Hevea brasiliensis genome using their mature sequences. Bioinformatics methods were employed to predict and analyze the secondary structure, phylogenetic relationships, and cis-acting elements in promoter regions of these family members, and real-time fluorescence quantitative PCR was used to detect expression levels of miR396 at different time under ethrel treatment. 【Result】 A total of 14 miR396 family members were identified in Hevea brasiliensis genome through genome-wide screening, whose mature forms were named hbr-miR396a to hbr-miR396l. The hbr-miR396b contained two mature forms hbr-miR396b-5p and hbr-miR396b-3p while hbr-miR396k contained two mature forms hbr-miR396k-5p and hbr-miR396k-3p. All these precursors of miR396 family members could form typical stem-loop structures and unevenly distributed across nine chromosomes. Phylogenetic analysis showed that the precursor sequences of this family exhibited genetic diversity, whilst the mature sequences within the same species showed a certain degree of conservation during evolution. The promoter regions of 14 miR396 family members contained numerous hormone response elements, defence and stress response elements, and light response elements, suggesting their involvement in hormone response, stress response, and developmental regulation. Among the miR396 family members in Hevea brasiliensis, only hbr-miR396b-5phbr-miR396e, and hbr-miR396k-5p were highly expressed in latex. The expression of hbr-miR396e and hbr-miR396k-5p continued to increase with prolonged ethephon treatment, while the expression of hbr-miR396b-5p was down-regulated after 6 h post-treatment and up-regulated again. Target gene prediction results indicated that the expression of most target genes was down-regulated during ethephon treatment, and this was contrary to the expression trends of the highly abundant expression of Hevea brasiliensis miR396 family members, which was consistent with the miRNA silencing mechanism.GO functional annotation and KEGG signaling pathway enrichment analysis results confirmed that these target genes played their roles in brassinosterorid biosynthesis, leaf development, as well as fructose and mannose metabolism, and so on. 【Conclusion】 After ethephon treatment of tapping panel, Hevea brasiliensis miR396 family members regulate key biological processes such as stress response, latex synthesis, and hormone response through a complex multi-level regulatory network, exerting a great influence on latex metabolism. Among these, hbr-miR396b-5phbr-miR396ehbr-miR396k-5p may participate in ethylene response pathway in Hevea brasiliensis laticifers via differentiated regulatory mechanisms.

     

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