Figures (3)  Tables (3)

    • Figure 1. 

      Genetic schematic diagram of conventional hybrid breeding and haploid breeding methods.

    • Figure 2. 

      Molecular mechanisms of in vivo haploid induction.

    • Figure 3. 

      Applications of haploid induction in crop breeding.

    • Gene Source species Recipient species Phenotype
      PsASGR-BBML Pennisetum squamulatum Pennisetum glaucum 35%–36% parthenogenesis rate1* in T1[71]
      Oryza sativa 25%–89% parthenogenesis rate2* in T1[72]
      Zea mays 47%–80% parthenogenesis rate2* in T1[72]
      Arabidopsis 0[72]
      Nicotiana tabacum 2.7%–27.3% haploid rate3* in T2[73]
      BnBBM1 Brassica napus Arabidopsis 0.4% haploid rate3* in T1[74]
      Brassica napus 1.8 ± 0.6% haploid rate3* in T1[74]
      Solanum lycopersicon 1.4% haploid rate3* in T1[74]
      OsBBM1 Oryza sativa Oryza sativa 5%–10% haploid rate3* in T1, 29% haploid rate3* in T2[75]
      OsBBM4 Oryza sativa Oryza sativa 3.2% haploid rate3* in T1[76]
      ZmBBM1 Zea mays Zea mays 65% haploid rate3* in T1[77]
      ZmBBM2 Zea mays Zea mays 0.4%–3.6% haploid rate3* in T1[78]
      IbBBM Ipomoea batatas Ipomoea batatas 5%–7.1% haploid rate3* in T1[79]
      ToPAR Taraxacum officinale Lactuca sativa 15% parthenogenesis rate1* in T1[82]
      Setaria italica 1.4%–10.2% haploid rate3* in T1[83]
      OsWUS Oryza sativa Oryza sativa 20% parthenogenesis rate1* in T1[84]
      OsBBM1 Oryza sativa Oryza sativa 15.8% haploid rate4* in T1[49]
      NtBAR1 Nicotiana tabacum Nicotiana tabacum 3.6% haploid rate5* in tissue culture[49]
      1* Parthenogenesis rate = Number of ovaries with parthenogenic embryos/Number of ovaries. 2* Parthenogenesis rate = Number of transgenic lines with haploid embryo production/Number of transgenic lines. 3* Haploid rate = Number of haploids/Total number of seedlings. 4* Haploid rate = Number of androgenesis embryos/Number of mature anthers. 5* Haploid rate = Number of haploids/Number of microspores.

      Table 1. 

      List of parthenogenesis genes inducing haploids when specifically expressed.

    • Gene Source species Function Haploid inducer parent Haploid induction rate (HIR) (%)
      ig1 Zea mays LOB domain transcription factor, expressed in embryo sac Paternal up to 3.3[60]
      MTL/ZmPLA1/NLD Zea mays Phospholipase A, expressed in endo-PM of the vegetative cell Paternal 2–6.7[19−21]
      POD65 Zea mays Peroxidase, expressed in pollen Paternal 1–7.7[30]
      PLD3 Zea mays Phospholipase D3, expressed in pollen Paternal 0.85–0.96[32]
      PLDα2 Oryza sativa Phospholipase D, expressed in pollen Paternal 0.3–0.6[33]
      DMP Zea mays DUF679 domain membrane protein, expressed in pollen Paternal 0.1–0.3[34]
      KPL Arabidopsis Natural cis-antisense siRNA-encoding gene, expressed in pollen Paternal 0.07–0.34[47]
      ECS1/2 Arabidopsis Aspartic endopeptidases, expressed in egg cell Maternal ~1[65,66]
      pPLAIIγ Arabidopsis Phospholipase A, expressed in gynoecium Maternal 0.93–1.12[67]
      ZmGEX1 Zea mays Versatile membrane protein, expressed in gamete Maternal 0.49–1.94[68]
      CENH3 Arabidopsis Centromeric histone 3, expressed in centromere Maternal ~30[89]
      Paternal ~4[89]
      KNL2 Arabidopsis Centromere licensing factor Maternal 1–10[99]

      Table 2. 

      List of genes inducing haploids when knocked out.

    • Species Method Setting percentage (%) Clone seed ratio (%)
      Arabidopsis Crossing MiMe plants with GEM line ND 33[130]
      Oryza sativa Simultaneous editing MiMe genes in BBM1 transgene plants (MiMe + OsBBM1-ee) ND 11–29[75]
      Oryza sativa Simultaneous editing MiMe genes and MTL in hybrid rice (Fix1) 3.7–5.2 4.7–9.5[134]
      Oryza sativa Simultaneous editing MiMe genes and expressing egg-cell specific BBM4 (Fix2) 80.9–86.1 1.3–2.4[76]
      Oryza sativa Simultaneous editing MiMe genes and expressing egg-cell specific PAR 74.4–82.8 42.9–67.7[132]
      Arabidopsis Simultaneous editing MiMe genes, AtDMP8 and AtDMP9 (AtFix1) 10–24 3.8[131]
      Oryza sativa Editing MiMe genes, and expressing egg-cell specific enhanced BBM1 (MiMe-ECA1-AZP2) Up to 89.7 95–100[133]
      Oryza sativa Simultaneous editing MiMe genes and expressing egg-cell specific OsWUS (Fix3) 72.0–85.2 0.5–21.7[84]
      Oryza sativa Simultaneous editing MiMe genes and OsPLDα2 in hybrid rice (Fix4) 82.1–85.0 1.2[33]
      'ND' indicates not shown in the literature.

      Table 3. 

      List of methods inducing apomixis.