unreduced gamete formation and its role in plant breeding
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This document discusses unreduced gamete formation and its role in plant breeding. It begins with an introduction and overview of unreduced gametes, also called 2n gametes, which have the same chromosome number as the parent plant. It then covers sources and mechanisms of 2n gamete formation, including interspecific hybrids, meiotic mutants, and odd polyploids. The mechanisms of 2n gamete formation through mitosis and various types of meiotic restitution are explained. Detection methods and factors that influence 2n gamete frequency are outlined. The role of 2n gametes in plant breeding applications such as ploidy level manipulation, inter-genomic recombination, and development of new crop varieties is then
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unreduced gamete formation and its role in plant breeding
- 1. 1
- 2. 2 Unreduced gamete formation and Its role in plant breeding
- 3. 3 Introduction 2n gametes Sources and mechanisms Detection and induction Role in plant breeding Conclusion In this mother cell…
- 6. An unreduced gamete has the same chromosome number as the plant that produced it i.e., 2n They are also called 2n gamets or diplogametes It is genetically controlled and results of modification of meiotic process Contributed little to the origin of polyploids Unreduced gametes 6
- 7. Sources of 2n gametes Interspecific hybrids: both 2n egg and pollen are produced simultaneously by the same hybrid. but, neither of two parents of the F1 hybrid nor their F2 sexual polyploidy progenies can produce 2n gamets. Ex: Lilium ( Barba-Gonzalez et al., 2005) Wheat (Xu & Joppa, 2000; Zhang et al., 2010) Citrus (Chen et al., 2008) 7
- 8. Meiotic mutants A mutant active gene in meiosis 2n pollen can formed independent from 2n egg cells and vice versa. Ex: Potato (Jongedijk et al., 1991; Peloquin et al., 1999), Red clover (Parrot & Smith, 1984), Alfalfa (Barcaccia et al., 2003), Wheat (Jauhar, 2003; Roberts et al., 1999) Arabidopsis (d’ Erfurth et al., 2008; Yang et al., 1999) 8
- 9. Odd polyploids : Crosses with triploids (gametes can be 1x, 2x or 3x) result in higher ploidy levels of the progeny and mostly act as a bridge between diploids and tetraploids (Kohler, et al., 2010) 9
- 10. Mechanisms of 2n gamete formation Mitotic mechanism: Somatic doubling, either obtained spontaneously or by the application of chemicals at zygotic, embryonic or meristematic stage of a plants life cycle. This will ultimately lead to the production of polyploid tissues and possibly the generation of polyploid offsprings. Ex: Citrus Frequency of polyploids in citrus cultivars (Usman , et al., 2006) 10
- 11. Meiotic mechanisms: Most commonly arise through meiotic defects Abnormal meiotic processes resulting in gametes that have the same chromosome number as that of parent plant This is mainly due to Meiotic Nuclear Restitution (MNR) 11
- 12. 1. First division restitution (FDR) 2. Second division restitution (SDR) 3. Indeterminate meiotic restitution (IMR) 4. Post meiotic restitution (PMR) Other cytological aspects- FDR and SDR Cytomixis Pre-meiotic doubling 4 types- 12
- 13. (Brownfield and Kohler, 2010) 13
- 14. Products of meiotic restitutions (Gómez-Rodríguez, et al.,2012) 14
- 15. Indeterminate meiotic restitution (IMR) Display a mixture of FDR and SDR. Failure of chromosome pairing A part sister chromosome move to the same daughter cell. The parental genomes are present in odd numbers. 15
- 16. 16
- 17. Cytological aspects: Other than FDR and SDR- Cytomixis : chromatin from the nucleus extrudes to cytoplasm of adjacent mother cell through cytoplasmic connections (Sheidai et al., 2006) . Pre- meiotic doubling: before meiosis a doubling of the chromosomes occur (Woogenvoort et al., 1990). 17
- 18. Genes involved in 2n gamete formation 1. SWI1/DYAD 2. CYCA1;2/TAM 3. OSD1 4. AtPS1 5. dif1-1 6. PS- potato 7. el - maize A. thaliana 18
- 19. (Brownfield and Kohler, 2010) 19
- 20. (A) Metaphase I (B) dif1-1 (C) swi1-2 (D,E) swi1-2/dif1-1 double mutant meiocytes. (D) Sister chromatid cohesion is lost at the end of prophase I. (E) The resulting 20 free chromatids at metaphaseI. (F) Some cells contained 10 condensed univalents. (Mercier et al., 2003) 20
- 21. Frequency of unreduced gamete production (Number of individuals producing 2n gametes/total number of individuals examined) (Bretagnolle and Thompson, 1995) 21
- 22. Factors affecting frequency of unreduced gamete production Stimulated by environmental factors such as temperature, wounding, water and nutrient stress…… Formation of giant pollen in Brassica inter specific hybrids more viable than normal. frequency is high under cold temperatures these are two times greater than parents in terms of magnitude 22
- 23. (Mason et al.,2011) Male unreduced gamete production in Brassica species under different temperatures 23
- 24. Pollen viability estimates (Mason et al.,2011) 24
- 25. Techniques to increase frequency 25
- 26. Detection of 2n gametes 1. Pollen morphology 2. Flow cytometry 3. Analysis of sporogenesis 4. Ploidy analysis of the progeny 26
- 27. Pollen Morphology • Banana, rose (Rosa) and sweet potato 30% larger • Chinis jujube (Ziziphus jujube) 1.5 times larger (Xue et al., 2011) Search for large pollen in the population 27
- 28. 28(Xue et al., 2011)
- 29. FLOW CYTOMETRY Direct quantification of pollen nuclear DNA -practiced in Lilly, tobacco, maize and in rape –Pan et al., 2004 Compares the DNA content of pollen nuclei to the DNA content of somatic leaf tissue. 29
- 30. (Chen and Gmitter , 2011) 30
- 31. • Complex outer exine layer on the pollen surface is the main obstacle in releasing the nuclei from pollen. Bohne et al., 2003 Difficulties and solutions • Bead beating Roberts, 2007 • Chopping of pollen grains Laere et al., 2009 • Nuclear isolation protocol which only releases nuclei from germination tubes Dewitte et al. (2006, 2009) 31
- 32. Alternative method to confirm the presence of 2n pollen Analysis of microsporogenesis Provide insight in the mechanisms (FDR, SDR) behind 2n gamete formation. Molecular cytological techniques like GISH, FISH or AFLP markers can be used Draw back: does not provide any information about pollen viability. 32
- 33. Ploidy analysis of the progeny Chromosome counting method Flow cytometry 33
- 34. Induction of 2n gametes (Dewitte et al., 2012) 34
- 35. (Nukui, et al., 2011) 35
- 36. (Nukui et al., 2011) Restoration of fertility in interspecific hybrids by N2O 36 Untreated N2O Treated
- 37. (Barba-Gonzalez et al., 2006) UNTREATED N2O TREATED Germination of 2n pollen 37
- 38. Trifluralin treatment • Induced 2n pollen by submerging flower buds of Begonia in a trifluralin solution. Dewitte et al. (2010) • Spraying maize tassels with a trifluralin solution before flowering Kato, (1999) • Induction of both 2n pollen and 2n egg cells 38
- 39. Effect of temperature (Pecrix et al., 2011) 39
- 40. Hibiscus syriacus Hibiscus paramutabilis Interspecific hybridisation All are tetraploids 50% are hexaploids (Van Laere et al., 2009) 40
- 41. Tools to engineer 2n gamete formation Isolation of genes involved in 2n gamete production Site-directed mutagenesis Ethyl methane sulphonate (EMS) Random insertional mutagenesis or irradiation of seeds or buds 41
- 42. ROLE OF 2n GAMETES IN PLANT BREEDING Polyploids that originate through the functioning of 2n gametes (Peloquin, et al., 1999) 42
- 43. Ploidy level manipulations in potato (Carputo and Barone, 2005) 43
- 44. Inter-genomic recombination (Barba-Gonzalez et al., 2006) 44
- 45. Interspecific Lilium hybrids (Barba-Gonzalez et al., 2008) 2n gamete X diploid F1 2n gamete X tetraploid F1 45
- 46. Use of 2n gametes in potato germplasm introgression (Carputo, et al., 2000) 46
- 47. AA CCBB AABB AACC BBCC B. rapa B. oleraceaB. nigra B. juncea B. napus B. carinata AABBCC Super Brassica Breeding “Super Brassica” cultivars (Yan and Shyama , 2007) 47
- 48. B. napus (AnAnCnCn) X B. carinata (BcaBcaCcaCca) AnCn BcaCcaGametes: AnBcaCcaCn Unbalanced tetraploid X B. juncea (AjAjBjBj) Gametes: AnBcaCcaCn AjBj Unreduced gametes AnAjBjBcaCcaCn allohexaploids (Yan and Shyama , 2007) 48
- 49. Amphihaploids in wheat (Jauhar, 2007) 49
- 50. 50
- 51. 51
Editor's Notes
- #9: As different genes are active with in the micro- or macro- sporogenesis. might disturb during spindle formation or cytokinesis resulting in 2n gamets.
- #15: Meiotic restitution mechanisms in A. tequilana and A. angustifolia.
- #18: 1 in that way mother cell start meiosis with double amount of chromosomes (4x) resulting in unreduced gametes (2x). 2 this can takes place in pre meiotic mitosis due to failure in spindle formation
- #19: 1. protein is required in prophase I where it has roles in sister chromatid cohesion and recombination. A lack of SWI1/DYAD can result in an equational division involving the separation of sister chromatids at meiosis I and no further progression in female meiosis. 2. Supress the meiosis 2 2n egg formation is under the control of the el allele (Rhoades and Dempsey, 1966) 3. protein required for meiosis II entry 6. extensive chromosome fragmentation during meiosis
- #21: 1in a wild-type male meiocyte. Five bivalents are observed. 2meiocyte exhibiting chromosome fragmentation. 3meiocyte at the end of prophase. Twenty chromatids are observed.
- #28: The presence of large pollen only indicates the presence of 2n pollen but does not present proof of doubled DNA content. Another disadvantage of this screening technique is the broad overlap in size distribution between small and large pollen in some genera such as grasses.
- #33: use of molecular cytological techniques (genomic in situ hybridization, GISH or fluorescent in situ hybridization, FISH) or marker analysis (such as amplified fragment length polymorphism, AFLP) on meiocytes or polyploid progenymay provide more accurate or additional information on the mechanisms behind 2n gamete formation
- #35: major drawback to use 2n gametes in plant breeding is that only a minority of genotypes regularly produce 2n gametes
- #36: Size distribution, appearance, and flow cytometry histograms of pollen grains in diploid cultivars. two peaks corresponding to 1C and 2C DNA content because the binucleate-type lily pollen contains one 2C generative and one 1C vegetative cell (Fig. 1G). In contrast, the N2O-induced pollen gave rise to peaks at 1C, 2C and additional 4C levels, indicating both n and 2n pollen (Fig. 1H).
- #37: Overcoming hybrid sterility by treating sterile or partially sterile hybrid lilies with N2O for 48 h. N2O treatment is also expected to restore the fertility of interspecific hybrids through meiotic restitution or mitotic amphidiploidization. it is unknown how N2O treatment restores fertility in sterile hybrids.
- #39: . As such, the generative nucleus was mitotically arrested and viable bicellular pollen was obtained
- #40: disturbed meiosis resulted in the production of dyads and triads which mainly resulted from spindle misorientations in meiosis II.
- #45: There was a clear indication that N2O had induced restitution gametes in these cases but not chromosome doubling in pre-meiotic stages
- #46: Recombination among the parental genomes was present and as a result there is an enormous variation among the progeny Due to autosyndetic pairing there is no variation among the progeny