Table 1.
Genes underlying reproductive barriers in plants, with complementary genes indicated by superscript numbers
| Gene | Normal function | Organism | Level | Barrier phenotype | Likely genetic cause | Reference |
|---|---|---|---|---|---|---|
| Genes that underlie pre-pollination barriers | ||||||
| ANTHOCYANIN-2 (AN2) – a myb-type transcription factor | Regulation of anthocyanin production (floral colour) | Petunia axillaris/P. integrifolia | Inter-specific | Flower colour differences leading to pollinator shift | Loss of function mutations in coding sequence | (Quattrocchio et al., 1999; Hoballah et al., 2007) |
| ROSEA1, ROSEA2 and VENOSA – all are myb-type transcription factors | Regulation of anthocyanin production (floral colour) | Antirrhinum species | Inter-specific | Flower colour differences leading to shifts in pollinator fauna | ? | (Schwinn et al., 2006) |
| FLAVONOID-3′-HYDROXYLASE (F3′H) | Key enzyme in anthocyanin pathway (floral colour) | Ipomea species | Inter-specific | Flower colour differences leading to pollinator shift | cis-regulatory mutations that downregulate F3′H | (Des Marais and Rausher, 2010) |
| FLOWERING LOCUS C (FLC) – a MADS-box transcription factor | Represses flowering | Allopolyploid A. suecica isolated from parental species, A. thaliana and A. arenosa | Inter-specific | Delayed flowering of allopolyploid, A. suecica | cis-regulatory mutations in both A. thaliana and A. arenosa FLC | (Wang et al., 2006a) |
| STYLE2·1 – encodes a helix-loop-helix (HLH) | Transcription factor | Solanum lycopersicon/S. pennellii | Inter-specific | Recessed style leading to mating system shift outcrossing to selfing | cis-regulatory mutation(s) | (Chen et al., 2007) |
| Genes that underlie post-pollination prezygotic barriers | ||||||
| S-RNase-SI | Rejection of self pollen | Nicotiana species | Inter-specific | Rejection of pollen from other species | ? | (Murfett et al., 1996) |
| Genes that underlie intrinsic postzygotic barriers: hybrid inviability | ||||||
| 1Cf2 – an extracellular leucine-rich repeat receptor-like gene | Resistance to fungal pathogen | Solanum lycopersicon/S. pimpinellifolium | Inter-specific | Hybrid necrosis | Gene copy number variation | (Dixon et al., 1996; Kruger et al., 2002) |
| 1RC3 – encodes an extracellular cysteine protease | Perception of fungal Avr proteins | Solanum lycopersicon/S. pimpinellifolium | Inter-specific | Hybrid necrosis | Changes in protein sequence | (Kruger et al., 2002; Rooney, 2005) |
| DANGEROUS MIX 1 (DM1) – an NBS-LRR gene | Disease resistance | Arabidopsis thaliana | Intra-specific | Hybrid necrosis | Gene copy number variation | (Bomblies et al., 2007) |
| HISTIDINOL-PHOSPHATE AMINO-TRANSFERASE (HPA1 and HPA2) | Synthesis of essential amino acid, histidine | Arabidopsis thaliana | Intra-specific | Arrest of hybrid seed development | Reciprocal silencing of duplicate genes | (Bikard et al., 2009) |
| TRANSPARENT TESTA GLABRA2 (TTG2) – a WRKY transcription factor | Regulates epidermal cell fate | Arabidopsis thaliana | Intra-specific | Lethality of interploidal hybrids | cis-regulatory mutations | (Dilkes et al., 2008) |
| HBD2 – encodes a casein kinase | Root development and hormone sensitivity | Oryza sativa | Inter-sub-specific | Hybrid necrosis | Change in protein sequence | (Yamamoto et al., 2010) |
| HWH1 – encodes a GMC oxidoreductase | Catalyses oxidation–reduction reactions | Oryza sativa | Inter-sub-specific | Hybrid necrosis | ? | (Jiang et al., 2008) |
| Genes that underlie intrinsic postzygotic barriers: hybrid sterility | ||||||
| S5 – encodes an aspartate protease | Disease resistance signalling and cell death | Oryza sativa | Inter-sub-specific | Hybrid female sterility (embryo sac sterility) | Changes in protein sequence | (Chen et al., 2008) |
| 2SaM – a SUMO E3 ligase-like gene | Post-translational modification | Oryza sativa | Inter-sub-specific | Hybrid male sterility (pollen abortion) | Substitution in intron-splicing site, leading to truncated protein | (Long et al., 2008) |
| 2SaF – encodes an F-box protein | Mediation of protein-protein interactions | Oryza sativa | Inter-sub-specific | Hybrid male sterility (pollen abortion) | Amino acid substitution | (Long et al., 2008) |
| mtRPL27 – Nuclear-encoded mitochondrial ribosomal protein L27 | Translation of mitochondrial genes | Oryza sativa/O. glumaepatula | Inter-specific | Hybrid male sterility (pollen abortion) | Reciprocal silencing of duplicate genes | (Yamagata et al., 2010) |