合成无融合生殖:从理论构想到杂种优势固定

    Synthetic apomixis: From theoretical conception to heterosis fixation

    • 摘要: 合成无融合生殖(Synthetic apomixis)是指通过基因工程手段模拟天然无融合生殖过程,绕过减数分裂与受精,直接经由种子产生与母本遗传信息完全一致的克隆后代。其核心技术包含2个关键环节:1)构建有丝分裂替代减数分裂( Mitosis instead of meiosis, MiMe) 系统,通过同时突变3类基因,分别抑减数分裂DNA双链断裂的发生、促使姐妹染色单体提前分离和跳过第2次减数分裂,使植物产生遗传信息与亲本完全一致的二倍体配子;2)通过异位表达孤雌生殖相关基因(如BBM1PARHUAXU等)或利用单倍体诱导基因(如MTLDMPCENH3等),实现二倍体配子的胚胎发生。2个环节的成功组合可产生基因型与母本完全一致的克隆种子,从而实现杂种优势的固定。目前,MiMe系统已在拟南芥Arabidopsis thaliana、水稻Oryza sativa、番茄Solanum lycopersicum、玉米Zea mays、甘蓝型油菜Brassica napus和高粱Sorghum bicolor等物种中成功建立,但不同物种在3个减数分裂环节的最优基因组合上存在显著差异。迄今,高效的合成无融合生殖仅在水稻中实现,以“Fix”策略为代表,最高克隆种子诱导效率可达99%,但在其他物种中仍面临诸多挑战。本文系统综述了MiMe系统的分子基础及其物种特异性、孤雌生殖与单倍体诱导的各条途径及其效率、合成无融合生殖及其在主要作物中的应用,深入讨论了当前面临的核心挑战并展望了其在育种中的发展前景。

       

      Abstract: Synthetic apomixis is referred to use genetic engineering to resemble natural apomictic pathways, enabling the production of clonal offspring through seeds that are genetically identical to the maternal parents. This process bypasses meiosis and fertilization. The critical techniques involve two processes: 1) the established MiMe (Mitosis instead of Meiosis) system, which requires the simultaneous disruption of three genes, each of them abolishes the formation of DNA double-strand breaks for initiating homologous recombination, induces precocious separation of sister chromatids, and suppresses the second meiotic division, thus leading to the generation of diploid gametes that are clonal to the parent; 2) the induction of embryogenesis from these diploid gametes via ectopic expression of parthenogenesis-associated genes such as BBM1, PAR and HUAXU or haploid inducers such as MTL, DMP, or CENH3. The successful coupling of these two modules produces clonal seeds with an identical genotype to the mother plant, thus achieving the fixation of heterosis. To date, the MiMe system has been successfully established in Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa), tomato (Solanum lycopersicum), maize (Zea mays), rapeseed (Brassica napus), and sorghum (Sorghum bicolor), although the optimal combination of the three meiotic genes exhibits marked species-specific variation. Efficient synthetic apomixis has so far been realized only in rice, most notably through the “Fix” strategy, achieving a clonal seed induction efficiency of up to 99%. However, major challenges remain in other crop species. This review systematically summarizes the molecular basis and species-specific features of the MiMe system, the various routes and efficiencies of parthenogenesis and haploid induction, synthetic apomixis and its applications in major crops. We also discuss critical challenges and offer perspectives on the future application of synthetic apomixis in crop breeding.

       

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