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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

Key female gametophyte reproductive stages during flower development in 2x homoploid and 3x heteroploid synthetic hybrids (a–c), and natural 6x heteroploid hybrids (d, e) of Ranunculus. Ovule images are placed as in Supporting Information Fig. S1 so that rotation angles can be tracked by the orientation of the chalazal-micropylar axis. (a) Functional megaspore immediately after meiosis; (b) end of meiosis showing four meiotic products – the two located toward the micropyle are aborted whereas the other two show signs of abortion – and two putative aposporous initial cells; (c) completely rotated ovule showing a mature seven-celled embryo sac at blooming stage; (d) aborted germline and two aposporous initials in the chalazal area; (e) mature embryo sac just before polar nuclei fusion to form a secondary nucleus in the central cell. (f) Box-and-whisker diagram for the proportion of functional embryo sacs (ES) among ploidy levels of interspecific hybrids. Boxes represent first and third quartiles, and the band inside each box indicates the median. Whiskers correspond to 95% CI. Outliers and extreme values are represented by circles and stars, respectively. Genotypes: (a) J5; (b) J20; (c) G13; (d) HöC29; (e) HöC35. fm, functional megaspore; mp, row of four meiotic products; pai, putative aposporous initial cells; ec, egg cell; ai, aposporous initial cells; ii, inner integuments; •, chalazal pole; *, micropylar pole. Bar, 30 μm.
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fig01: Key female gametophyte reproductive stages during flower development in 2x homoploid and 3x heteroploid synthetic hybrids (a–c), and natural 6x heteroploid hybrids (d, e) of Ranunculus. Ovule images are placed as in Supporting Information Fig. S1 so that rotation angles can be tracked by the orientation of the chalazal-micropylar axis. (a) Functional megaspore immediately after meiosis; (b) end of meiosis showing four meiotic products – the two located toward the micropyle are aborted whereas the other two show signs of abortion – and two putative aposporous initial cells; (c) completely rotated ovule showing a mature seven-celled embryo sac at blooming stage; (d) aborted germline and two aposporous initials in the chalazal area; (e) mature embryo sac just before polar nuclei fusion to form a secondary nucleus in the central cell. (f) Box-and-whisker diagram for the proportion of functional embryo sacs (ES) among ploidy levels of interspecific hybrids. Boxes represent first and third quartiles, and the band inside each box indicates the median. Whiskers correspond to 95% CI. Outliers and extreme values are represented by circles and stars, respectively. Genotypes: (a) J5; (b) J20; (c) G13; (d) HöC29; (e) HöC35. fm, functional megaspore; mp, row of four meiotic products; pai, putative aposporous initial cells; ec, egg cell; ai, aposporous initial cells; ii, inner integuments; •, chalazal pole; *, micropylar pole. Bar, 30 μm.

Mentions: Ovule development in diploid (R. carpaticola × R. notabilis) and triploid (R. cassubicifolius × R. notabilis) hybrids (n = 910; Table 1) was structurally similar to that of sexual parents, but showed clear alterations in timing, and bias in the reproductive mode. Once started, sporogenesis and gametogenesis were delayed compared to parental species. At the end of meiosis, ovules were rotated c. 150° on the A–P axis in both diploid and triploid hybrids (Figs1a, S3d, Table S2), and a greater variance in rotation angles at this stage evidenced meiotic developmental asynchrony (Table S2). Megasporogenesis exhibited diverse developmental irregularities (e.g. arrested development and apoptosis in germ line cells at different points of meiosis, altered pattern of megaspore selection; Fig. S4a,b). When functional, meiosis ended in a triad (Fig. 1a), although dyads or tetrads were often observed. Functional megaspores were present in 67% of diploid ovules (n = 257; Table 1) and 69% of triploid ovules (n = 191; Table 1). At this stage, 11–15% of ovules showed enlarged somatic cells (i.e. putative aposporous initial or aposporous initial-like cells) in the nucellar tissue of diploids and triploids, respectively (Fig. 1b; Table 1). Putative aposporous cells appeared during meiosis, when apoptosis in meiotic germline was evident, or after meiosis at the 1-to-4 nuclei embryo sac stage.


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)

Key female gametophyte reproductive stages during flower development in 2x homoploid and 3x heteroploid synthetic hybrids (a–c), and natural 6x heteroploid hybrids (d, e) of Ranunculus. Ovule images are placed as in Supporting Information Fig. S1 so that rotation angles can be tracked by the orientation of the chalazal-micropylar axis. (a) Functional megaspore immediately after meiosis; (b) end of meiosis showing four meiotic products – the two located toward the micropyle are aborted whereas the other two show signs of abortion – and two putative aposporous initial cells; (c) completely rotated ovule showing a mature seven-celled embryo sac at blooming stage; (d) aborted germline and two aposporous initials in the chalazal area; (e) mature embryo sac just before polar nuclei fusion to form a secondary nucleus in the central cell. (f) Box-and-whisker diagram for the proportion of functional embryo sacs (ES) among ploidy levels of interspecific hybrids. Boxes represent first and third quartiles, and the band inside each box indicates the median. Whiskers correspond to 95% CI. Outliers and extreme values are represented by circles and stars, respectively. Genotypes: (a) J5; (b) J20; (c) G13; (d) HöC29; (e) HöC35. fm, functional megaspore; mp, row of four meiotic products; pai, putative aposporous initial cells; ec, egg cell; ai, aposporous initial cells; ii, inner integuments; •, chalazal pole; *, micropylar pole. Bar, 30 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig01: Key female gametophyte reproductive stages during flower development in 2x homoploid and 3x heteroploid synthetic hybrids (a–c), and natural 6x heteroploid hybrids (d, e) of Ranunculus. Ovule images are placed as in Supporting Information Fig. S1 so that rotation angles can be tracked by the orientation of the chalazal-micropylar axis. (a) Functional megaspore immediately after meiosis; (b) end of meiosis showing four meiotic products – the two located toward the micropyle are aborted whereas the other two show signs of abortion – and two putative aposporous initial cells; (c) completely rotated ovule showing a mature seven-celled embryo sac at blooming stage; (d) aborted germline and two aposporous initials in the chalazal area; (e) mature embryo sac just before polar nuclei fusion to form a secondary nucleus in the central cell. (f) Box-and-whisker diagram for the proportion of functional embryo sacs (ES) among ploidy levels of interspecific hybrids. Boxes represent first and third quartiles, and the band inside each box indicates the median. Whiskers correspond to 95% CI. Outliers and extreme values are represented by circles and stars, respectively. Genotypes: (a) J5; (b) J20; (c) G13; (d) HöC29; (e) HöC35. fm, functional megaspore; mp, row of four meiotic products; pai, putative aposporous initial cells; ec, egg cell; ai, aposporous initial cells; ii, inner integuments; •, chalazal pole; *, micropylar pole. Bar, 30 μm.
Mentions: Ovule development in diploid (R. carpaticola × R. notabilis) and triploid (R. cassubicifolius × R. notabilis) hybrids (n = 910; Table 1) was structurally similar to that of sexual parents, but showed clear alterations in timing, and bias in the reproductive mode. Once started, sporogenesis and gametogenesis were delayed compared to parental species. At the end of meiosis, ovules were rotated c. 150° on the A–P axis in both diploid and triploid hybrids (Figs1a, S3d, Table S2), and a greater variance in rotation angles at this stage evidenced meiotic developmental asynchrony (Table S2). Megasporogenesis exhibited diverse developmental irregularities (e.g. arrested development and apoptosis in germ line cells at different points of meiosis, altered pattern of megaspore selection; Fig. S4a,b). When functional, meiosis ended in a triad (Fig. 1a), although dyads or tetrads were often observed. Functional megaspores were present in 67% of diploid ovules (n = 257; Table 1) and 69% of triploid ovules (n = 191; Table 1). At this stage, 11–15% of ovules showed enlarged somatic cells (i.e. putative aposporous initial or aposporous initial-like cells) in the nucellar tissue of diploids and triploids, respectively (Fig. 1b; Table 1). Putative aposporous cells appeared during meiosis, when apoptosis in meiotic germline was evident, or after meiosis at the 1-to-4 nuclei embryo sac stage.

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