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Emergence of apospory and bypass of meiosis via apomixis after sexual hybridisation and polyploidisation.

Hojsgaard D, Greilhuber J, Pellino M, Paun O, Sharbel TF, Hörandl E - New Phytol. (2014)

Bottom Line: Bypassing meiosis permits these triploid genotypes to form viable seed and new polyploid progeny.Apomixis is functional in triploids and associated with drastic meiotic abnormalities.Selection acts to stabilise developmental patterns and to tolerate endosperm dosage balance shifts which facilitates successful seed set and establishment of apomictic lineages.

View Article: PubMed Central - PubMed

Affiliation: Department of Systematics, Biodiversity and Evolution of Plants, Albrecht-von-Haller Institute for Plant Sciences, Georg August University of Göttingen, Untere Karspüle 2, D-37073, Göttingen, Germany.

No MeSH data available.


Related in: MedlinePlus

Flow cytometry histograms of seeds produced by diploid Ranunculus carpaticola × R. notabilis (a) and triploid R. cassubicifolius × R. notabilis hybrids (b–e). In all histograms: peak 1, nuclei from the embryo tissue; peak 2, nuclei from the endosperm tissue; peak 3, dividing cells of the embryo tissue in G2 phase of the mitotic cycle. (a) Sexual seed from a diploid mother plant with a diploid embryo (c. 35 in x-axis) and a triploid endosperm (c. 50 in x-axis) formed by fertilisation of a reduced female gametophyte; (b) sexual seed from a triploid mother plant with a near diploid embryo and a near triploid endosperm formed after fusion of near haploid gametes; (c) sexual seed from a triploid plant, with a triploid embryo and a hexaploid endosperm formed by polyspermy; (d) apomictic seed from a triploid mother plant, with a triploid embryo formed by parthenogenesis and a near octoploid (c. 7.5x) endosperm formed by fertilisation of a hexaploid secondary polar nucleus derived from an unreduced central cell; (e) partial apomictic seed from a triploid plant, with a near tetraploid embryo (c. 4.4x) and a near heptaploid endosperm (c. 7.4x) formed by fertilisation of a hexaploid secondary polar nucleus derived from an unreduced central cell; (f) plot representing the variety of cytological pathways of seed formation observed in diploid and polyploid materials according to peak indexes and ploidy of embryos. syn, synthetic genotypes; nat, natural genotypes. Genotypes: (a) F11; (b) G6; (c) G12; (d) G1; (e) I9.
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fig03: Flow cytometry histograms of seeds produced by diploid Ranunculus carpaticola × R. notabilis (a) and triploid R. cassubicifolius × R. notabilis hybrids (b–e). In all histograms: peak 1, nuclei from the embryo tissue; peak 2, nuclei from the endosperm tissue; peak 3, dividing cells of the embryo tissue in G2 phase of the mitotic cycle. (a) Sexual seed from a diploid mother plant with a diploid embryo (c. 35 in x-axis) and a triploid endosperm (c. 50 in x-axis) formed by fertilisation of a reduced female gametophyte; (b) sexual seed from a triploid mother plant with a near diploid embryo and a near triploid endosperm formed after fusion of near haploid gametes; (c) sexual seed from a triploid plant, with a triploid embryo and a hexaploid endosperm formed by polyspermy; (d) apomictic seed from a triploid mother plant, with a triploid embryo formed by parthenogenesis and a near octoploid (c. 7.5x) endosperm formed by fertilisation of a hexaploid secondary polar nucleus derived from an unreduced central cell; (e) partial apomictic seed from a triploid plant, with a near tetraploid embryo (c. 4.4x) and a near heptaploid endosperm (c. 7.4x) formed by fertilisation of a hexaploid secondary polar nucleus derived from an unreduced central cell; (f) plot representing the variety of cytological pathways of seed formation observed in diploid and polyploid materials according to peak indexes and ploidy of embryos. syn, synthetic genotypes; nat, natural genotypes. Genotypes: (a) F11; (b) G6; (c) G12; (d) G1; (e) I9.

Mentions: In total, embryo and endosperm ploidies of 1396 seeds from three diploid parents, 10 natural hexaploid and 25 synthetic hybrids, representing 15 diploid and 10 triploid genotypes, were analysed by flow cytometry (Tables2, 3). Endosperm-to-embryo peak indexes revealed the nature of seed formation pathways. Around 29% of 734 seeds from hexaploid natural hybrids were sexually produced (peak indexes ranged c. 1.5–2; 2m : 1p contributions to the endosperm; Table 2). The remaining seeds showed peak indexes between c. 2.5 and 3 due to the participation of unreduced female gametophytes in zygote formation plus one or two sperms in endosperm formation (relative contributions of 4m : 1p and 2m : 1p to the endosperm, respectively; Tables2, 3). Natural diploid parents and newly formed diploid hybrids consistently produced sexual seeds (n = 30 and n = 501, respectively, 2m : 1p contributions to the endosperm; Tables2, 3) (Fig. 3a). However, triploid hybrids showed a variety of functional cytological pathways for seed formation. Analysis of reproductive pathways, ploidy ranges in embryos and parental contributions to endosperm (Tables2, 3) indicated that most seeds were sexually derived, with near diploid or near triploid embryos resulting from the fusion of near haploid or hyperhaploid male and female gametes carrying unbalanced aneuploid chromosome sets (unbalanced meiosis + syngamy; n = 50; c. 2m : 1p contributions to the endosperm; Fig. 3b, Table 3). Some seeds carried triploid embryos (3x; n = 8), of which three had near hexaploid endosperms (c. 6x) (Fig. 3c, Table 3), suggesting syngamy and polyspermy in the central cell involving either hyperhaploid female and male gametes (c. 1.5x), or a near diploid female gamete and near haploid male gametes (unbalanced meiosis + syngamy + polyspermy) (Fig. 3f; Tables2, 3). Two seeds with triploid embryos developed apomictically from an unreduced, unfertilised egg cell and a fertilised central cell (apospory, parthenogenesis + pseudogamy; 3x embryo, c. 7.5x endosperm; c. 4m : 1p contributions to the endosperm; Fig. 3d; Table 2). One seed had a near tetraploid embryo (c. 4.4x), which was formed after fertilisation of an unreduced embryo sac by two reduced male gametes (c. 1.4x), one fused the egg cell and the other one the central cell (apospory + double fertilisation; BIII formation pathway; Asker & Jerling, 1992; c. 7.4x endosperm; c. 4m : 1p contributions to the endosperm; Fig. 3e; Table 3). The variety of cytological pathways, gamete ploidies and relative parental contributions involved in seed formation demonstrates the diversification in functional reproductive strategies shown in polyploid Ranunculus hybrids.


Emergence of apospory and bypass of meiosis via apomixis after sexual hybridisation and polyploidisation.

Hojsgaard D, Greilhuber J, Pellino M, Paun O, Sharbel TF, Hörandl E - New Phytol. (2014)

Flow cytometry histograms of seeds produced by diploid Ranunculus carpaticola × R. notabilis (a) and triploid R. cassubicifolius × R. notabilis hybrids (b–e). In all histograms: peak 1, nuclei from the embryo tissue; peak 2, nuclei from the endosperm tissue; peak 3, dividing cells of the embryo tissue in G2 phase of the mitotic cycle. (a) Sexual seed from a diploid mother plant with a diploid embryo (c. 35 in x-axis) and a triploid endosperm (c. 50 in x-axis) formed by fertilisation of a reduced female gametophyte; (b) sexual seed from a triploid mother plant with a near diploid embryo and a near triploid endosperm formed after fusion of near haploid gametes; (c) sexual seed from a triploid plant, with a triploid embryo and a hexaploid endosperm formed by polyspermy; (d) apomictic seed from a triploid mother plant, with a triploid embryo formed by parthenogenesis and a near octoploid (c. 7.5x) endosperm formed by fertilisation of a hexaploid secondary polar nucleus derived from an unreduced central cell; (e) partial apomictic seed from a triploid plant, with a near tetraploid embryo (c. 4.4x) and a near heptaploid endosperm (c. 7.4x) formed by fertilisation of a hexaploid secondary polar nucleus derived from an unreduced central cell; (f) plot representing the variety of cytological pathways of seed formation observed in diploid and polyploid materials according to peak indexes and ploidy of embryos. syn, synthetic genotypes; nat, natural genotypes. Genotypes: (a) F11; (b) G6; (c) G12; (d) G1; (e) I9.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4260133&req=5

fig03: Flow cytometry histograms of seeds produced by diploid Ranunculus carpaticola × R. notabilis (a) and triploid R. cassubicifolius × R. notabilis hybrids (b–e). In all histograms: peak 1, nuclei from the embryo tissue; peak 2, nuclei from the endosperm tissue; peak 3, dividing cells of the embryo tissue in G2 phase of the mitotic cycle. (a) Sexual seed from a diploid mother plant with a diploid embryo (c. 35 in x-axis) and a triploid endosperm (c. 50 in x-axis) formed by fertilisation of a reduced female gametophyte; (b) sexual seed from a triploid mother plant with a near diploid embryo and a near triploid endosperm formed after fusion of near haploid gametes; (c) sexual seed from a triploid plant, with a triploid embryo and a hexaploid endosperm formed by polyspermy; (d) apomictic seed from a triploid mother plant, with a triploid embryo formed by parthenogenesis and a near octoploid (c. 7.5x) endosperm formed by fertilisation of a hexaploid secondary polar nucleus derived from an unreduced central cell; (e) partial apomictic seed from a triploid plant, with a near tetraploid embryo (c. 4.4x) and a near heptaploid endosperm (c. 7.4x) formed by fertilisation of a hexaploid secondary polar nucleus derived from an unreduced central cell; (f) plot representing the variety of cytological pathways of seed formation observed in diploid and polyploid materials according to peak indexes and ploidy of embryos. syn, synthetic genotypes; nat, natural genotypes. Genotypes: (a) F11; (b) G6; (c) G12; (d) G1; (e) I9.
Mentions: In total, embryo and endosperm ploidies of 1396 seeds from three diploid parents, 10 natural hexaploid and 25 synthetic hybrids, representing 15 diploid and 10 triploid genotypes, were analysed by flow cytometry (Tables2, 3). Endosperm-to-embryo peak indexes revealed the nature of seed formation pathways. Around 29% of 734 seeds from hexaploid natural hybrids were sexually produced (peak indexes ranged c. 1.5–2; 2m : 1p contributions to the endosperm; Table 2). The remaining seeds showed peak indexes between c. 2.5 and 3 due to the participation of unreduced female gametophytes in zygote formation plus one or two sperms in endosperm formation (relative contributions of 4m : 1p and 2m : 1p to the endosperm, respectively; Tables2, 3). Natural diploid parents and newly formed diploid hybrids consistently produced sexual seeds (n = 30 and n = 501, respectively, 2m : 1p contributions to the endosperm; Tables2, 3) (Fig. 3a). However, triploid hybrids showed a variety of functional cytological pathways for seed formation. Analysis of reproductive pathways, ploidy ranges in embryos and parental contributions to endosperm (Tables2, 3) indicated that most seeds were sexually derived, with near diploid or near triploid embryos resulting from the fusion of near haploid or hyperhaploid male and female gametes carrying unbalanced aneuploid chromosome sets (unbalanced meiosis + syngamy; n = 50; c. 2m : 1p contributions to the endosperm; Fig. 3b, Table 3). Some seeds carried triploid embryos (3x; n = 8), of which three had near hexaploid endosperms (c. 6x) (Fig. 3c, Table 3), suggesting syngamy and polyspermy in the central cell involving either hyperhaploid female and male gametes (c. 1.5x), or a near diploid female gamete and near haploid male gametes (unbalanced meiosis + syngamy + polyspermy) (Fig. 3f; Tables2, 3). Two seeds with triploid embryos developed apomictically from an unreduced, unfertilised egg cell and a fertilised central cell (apospory, parthenogenesis + pseudogamy; 3x embryo, c. 7.5x endosperm; c. 4m : 1p contributions to the endosperm; Fig. 3d; Table 2). One seed had a near tetraploid embryo (c. 4.4x), which was formed after fertilisation of an unreduced embryo sac by two reduced male gametes (c. 1.4x), one fused the egg cell and the other one the central cell (apospory + double fertilisation; BIII formation pathway; Asker & Jerling, 1992; c. 7.4x endosperm; c. 4m : 1p contributions to the endosperm; Fig. 3e; Table 3). The variety of cytological pathways, gamete ploidies and relative parental contributions involved in seed formation demonstrates the diversification in functional reproductive strategies shown in polyploid Ranunculus hybrids.

Bottom Line: Bypassing meiosis permits these triploid genotypes to form viable seed and new polyploid progeny.Apomixis is functional in triploids and associated with drastic meiotic abnormalities.Selection acts to stabilise developmental patterns and to tolerate endosperm dosage balance shifts which facilitates successful seed set and establishment of apomictic lineages.

View Article: PubMed Central - PubMed

Affiliation: Department of Systematics, Biodiversity and Evolution of Plants, Albrecht-von-Haller Institute for Plant Sciences, Georg August University of Göttingen, Untere Karspüle 2, D-37073, Göttingen, Germany.

No MeSH data available.


Related in: MedlinePlus