人工创制植物无融合生殖的研究进展

Research advances on plant synthetic apomixis

无融合生殖(apomixis)是指植物绕过正常减数分裂与受精过程形成克隆种子的一种无性生殖方式.无融合生殖具有固定杂种优势的潜力,长期以来一直是研究的热点.但是,由于其形成机制复杂一直未能取得突破.在深入研究植物有性生殖机制的基础上,通过人工设计创制无融合生殖有望成为实现杂种优势固定的一个可能途径.研究发现,同步突变多个减数分裂关键基因可以将减数分裂过程转换为类似有丝分裂过程,产生与母本遗传背景完全一致的克隆配子(mitosis instead of meiosis,Mi Me);在Mi Me背景下引入特殊的基因组消除系或编辑诱导孤雌生殖的关键基因能够成功实现无融合生殖.本文对无融合生殖技术的研究进展进行了总结,并对今后无融合生殖技术的改良以及将其在作物育种中的应用进行了讨论.

Heterosis,a phenomenon in which hybrid offspring shows better performance in many aspects than either of their homozygous parents,has been widely applied for improving crop productivity and adaptability.However,progenies generated via sexual reproduction are diverse owing to the genetic recombination during meiosis,which is not conducive to the application of heterosis.Apomixis is a type of asexual reproduction through which plants can produce clonal seeds without undergoing normal meiosis and fertilization.Therefore,apomixis has been a research hotspot for a long time because of its potential in fixing heterosis.Over 400 plant species exhibit apomictic phenomena in nature,and many genes linked with apomictic loci have been discovered in various species.These genes are involved in distinct regulatory mechanisms of apomixis.Even after decades of effort,these genes have not been successfully applied for crop apomixis because of complexity of the underlying mechanisms and lack of apomictic crops in nature.Due to the apomixis of plants also can be induced artificially by allowing plants to undergo unusual meiosis and fertilization,synthetic apomixis based on reproductive mechanisms has been proposed to fix heterosis.In Mi Me(mitosis instead of meiosis),meiotic division is completely replaced by a mitotic-like division and diploid gametes that are genetically identical to their mother are produced.Mi Me is induced by the absence of genes required for the pairing and recombination of homologous chromosomes,maintenance of sister chromatid cohesionas well as for the transition of germ cells from meiosis I to II.Following normal fertilization of clonal diploid gametes,the ploidy of offspring is doubled in each generation.To achieve synthetic apomixis and obtain clonal seeds,chromosome doubling following normal fertilization must be prevented.An effective way for this prevention is the elimination of one set of chromosomes from either parent.When a plant with altered CENH3(centromere-specific histone H3)protein is crossed with a wild-type plant,haploid progenies are induced through the elimination of chromosomes from the cenh3 mutant.Furthermore,combining Mi Me plants with a genome elimination line via crossing is an effective strategy to produce clonal seeds.In addition,upon expression of BBM1(BABY BOOM 1),which plays an important role in the initiation of embryogenesis,in the egg cell,haploid progenies are generated that produce seeds with haploid embryos following self-fertilization.Moreover,MTL(matrilineal)disruption in plants using CRISPR/Cas9 gene editing technology also can generate haploid progenies.Therefore,the combination of Mi Me with BBM1-or MTL-induced production of haploid progenies can achieve synthetic apomixis in plants and produce clonal seeds.In this review,we summarize advances in synthetic apomixis at the molecular level and discuss the improvement of synthetic apomixis as well as its potential application in crop breeding.