Self incompatibility in plants: a pollination control mechanism in plants
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Self incompatibility(SI) in plant plays important role in view of hybrid seed production. SI in this ppt have been explained in detail from its basics. The mechanism has been explained on the basis of conventional methods and molecular basis. It will be very useful for teaching and students.
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Self incompatibility in plants: a pollination control mechanism in plants
- 1. Mr. Vijayakumar B. Narayanapur Asst. Professor College of Horticulture, Sirsi University of Horticultural Sciences Bagalkot 587101 Dr Minimol J. S. Asst. Professor Cocoa Research Centre, Kerala Agricultural University Vellanikkara Thrissur 680656 1 Self-incompatibility: a pollination control mechanism in plants
- 2. Transfer of pollen from the male reproductive organ (anther) of one plant to the female reproductive organ (stigma) of another plant - cross pollination Transfer of pollen from the male reproductive organ (anther) of one plant to the female reproductive organ (stigma) of another plant - cross pollination 2
- 3. Mechanisms promoting cross pollination • Anemophily, hydrophily and entomophily • Dicliny or unisexuality - monoecy, dioecy • Dichogamy - protogyny and protandry • Male sterility • Self-incompatibility 3
- 4. “The prevention of fusion of fertile (functional) male and female gametes after self pollination” Gowers, 1989 Euphytica 4
- 5. Self-incompatibility: a pollination control mechanism in plants Vijayakumar B. Narayanapur 2015-22-002 Dept. of Plantation Crops and Spices Major Advisor: Dr. B. Suma Assoc. Professor Dept. of Plantation Crops and Spices 5
- 6. Contents • Introduction • Classification of self-incompatibility (SI) • Molecular basis of SI • SI genes with multiple alleles • Methods to assess SI • Significance of SI • Comparison between SI and male sterility • Limitation in exploiting SI • Methods to overcome SI • Summary • Future line of work 6
- 7. • First reported by Koelreuter (1850’s) • Genetic mechanisms of avoiding self fertilization • Natural out breeding system where self recognition and rejection is the rule • Promotes heterzygosity and prevents inbreeding depression • Based on allele specific-interaction between stigma receptors and pollen ligand Introduction 7
- 8. Distribution of self-incompatibility Nearly 6000 species 250 genera 70 families 19 orders - monocots and dicots Gowers, 1998 Hybrid Cultivar Development 8
- 9. Lewis,1954 Adv. Genet. Classification of self-incompatibility 9
- 10. Heteromorphic SI • Flowers of different incompatibility groups are different in morphology • Heteromorphic sporophytic system e.g. Primula Pin (ss), Thrum (Ss) 10
- 11. Contd…… Genotype of the plant (Sporophyte) Incompatibility reaction of pollen Incompatibility reaction of style Phenotype of flower Genotype of gametes 11
- 12. Mating Progeny Phenotype Genotype Genotype Phenotype Pin x Pin ss x ss Incompatible mating Pin x Thrum ss x Ss 1 Ss : 1 ss 1 Thrum : 1 Pin Thrum x Pin Ss x ss 1 Ss : 1 ss 1 Thrum : 1 Pin Thrum x Thrum Ss x Ss Incompatible mating Heteromorphic sporophytic SI Singh, 2012 Plant breeding Principles and Methods 12
- 13. Homomorphic SI • Not associated with morphological differences among flowers • Incompatibility reaction is controlled by – Genotype of the gametes - Gametophytic SI – Genotype of the plant - Sporophytic SI 13
- 14. East and Mangelsdorf, 1925 Proc. Nat. Acad. Sci. 14
- 15. S1S2 Anther S1S2 Pistil incompatible S1S3 Pistil semi-compatible S3S4 Pistil compatible Pollens Anther Stigma Style Ovary Ovule Gametophytic self-incompatibility S1 S2 S1 S2 S1 S2 Hughes and Babcock, 1950 Genetics 15
- 16. S1S2 Pistil Incompatible S1S3 Pistil Incompatible S3S4 Pistil Compatible S1S2 Anther Sporophytic self-incompatibility Hughes and Babcock, 1950 Genetics S1 (S1) S2 (S1) S1 (S1) S2 (S1) S1 (S1) S2 (S1) S1 S1 S3 16
- 17. Sporophytic self-incompatibility Crop References Kale Thompson, 1957 Radish Sampson, 1957 Broccoli Sampson, 1957 and Odland, 1962 Cabbage Adamson, 1965 Cauliflower Hoser-krauze, 1979 Cocoa Knight and Rogers, 1953 Tea Wilson et al., 1998 Mango Singh et al., 1962 17
- 18. Gametophytic SI Stigma is smooth and wet Genotype of the pollen (gamete) S-locus products are synthesized after completion of meiosis Growth of the pollen tube arrests in the style Sporophytic SI Stigma is papillate and dry Genotype of the sporophyte (diploid tissue) S-locus products are synthesized before completion of meiosis Growth of the pollen tube arrests at the surface of the stigma Comparison between gametophytic and sporophytic SI 18
- 19. S-locus controlling self-incompatibility Classical genetics S-locus was assumed to be a single gene Molecular studies after 1980’s At least two genes within S-locus One unit function as male, while other as female determinant Multigene complex is inherited as one unit Variants of gene complex are called “S-haplotypes” Expression of these genes are temporally (anthesis) and spatially (stigma) regulated 19
- 20. Female and male determinant genes Family Types of SI Male determinant Female determinant Brassicaceae SSI SP11/SCR SRK Solanaceae Rosaceae Scrophulariaceae GSI SLF/SFB S-RNase Papaveraceae GSI Unknown S-protein Takayama and Isogai, 2005 Annu. Rev. Plant Biol. SP11- S locus protein 11 SCR- S locus cysteine rich protein SRK- S locus receptor kinase SLF- S locus F-box protein SFB-S-haplotype-specific F-box protein 20
- 21. Molecular model of the SI in Brassicaceae Takayama and Isogai, 2005 Annu. Rev. Plant Biol. 21
- 22. S-locus or S related genes and gene function in Brassicaceae members S. No. S-locus related gene Gene function Species name Reference 1 SLG Doubtful B. oleracea Nasrallah, 2000 2 SRK Female determinant B. oleracea Stein et al., 1991 3 SP11/SCR Male determinant B. rapa Suzuki et al., 1999 4 MLPK Positive regulator B. rapa Murase et al., 2004 5 ARCI Positive regulator B. napus Stone et al., 2003 6 Rdr6 Positive regulator B. thaliana Tankikanjana, 2009 7 THLI Negative regulator B. napus Haffani et al., 2004 8 KAPP Putative SRK interactor B. oleracea Vanoosthuyse, 20039 SNXI Putative SRK interactor B. oleracea 10 Calmodulin Putative SRK interactor B. oleracea 11 PUB8 Putative SRK interactor A. thaliana Liu et al., 2007 12 sp locus Putative suprpressor B. napus Ma et al., 2009 22
- 23. Molecular model of the SI in Solanaceae Takayama and Isogai, 2005 Annu. Rev. Plant Biol. 23
- 24. Molecular model of the self-incompatibility in Papaveraceae (SBP-S protein-binding protein) Various reactions Takayama and Isogai, 2005 Annu. Rev. Plant Biol. 24
- 25. Crop No. of S alleles Type of SI Reference B. oleracea var. capitata 50 Sporophytic Bassett, 1986 B. campestris 30 Sporophytic Singh, 2012 Theobroma cacao 5 Late acting SI Knight and Rogers, 1953 Raphanus raphanistrum 9 Sporophytic SI Sampson, 1964 Trifolium pratensea 192 Gametophytic SI Paxman, 1963 Trifolium repens 71 Gametophytic SI Peter, 1991 Prunus avium 6 Gametophytic SI Choi et al., 2002 Raphanus sativus 32 Sporophytic SI Karron et al., 1989 Primula vulgaris 50 Sporophytic SI Robert et al., 1996 Trifolium pratens 50 Sporophytic SI Thomson, 1985 S locus with multiple alleles 25
- 26. Genetic hypothesis for SI allelic action in Theobroma cacao Clones- Pa 7, Pa 35 and Na 32 Five alleles S1 > S2 = S3> S4> S5 Genetic constitution Pa 7- S1 S5 Pa 35- S3 S5 Na 32- S2 S4 Knight and Rogers, 1953 Nature 26
- 27. Pa 35 S3 S5 Pa 7 S1 S5 S1S3 S1 S5 S3 S5 S5 S5 A B C S3 S5 S1 S5 Expected class – IV Identified in nature- III ( S1> S3> S5) Cross compatible relationship between Pa 35 and Pa 7 Knight and Rogers, 1953 Nature 27
- 28. S5 S2 S4 Pa 35 S3 S5 Na 32 S2 S4 S2S3 S3 S4 S2 S5 S4 S5 A B S3 Expected class – IV Identified in nature- II ( S2= S3>S4 >S5) Cross compatible relationship between Pa 35 and Na 32 Knight and Rogers, 1953 Nature 28
- 29. Methods to assess self-incompatibility in plants • Pollination methods • Cytological methods • Molecular methods 29
- 30. Varies depending upon the type of SI Pollination methods Cabbage Self the flower Wait for 60 days till the pod mature Count the number of seeds Cocoa Self 100 flowers tree-1 Wait for 14 days for the cherelle wilt 30
- 31. Cytological methods Cabbage No penetration of pollen tube to style-incompatible Penetration by intermediate number- semi compatible Penetration by many tubes- compatibility Incompatible Semi compatible Compatible 31
- 32. Cocoa Growth of pollen tube is similar in compatible and in-compatible type Tubes are traced down to the stylar canal of ovules In both type one male gamete fuse with endosperm Self-incompatible type second male gamete will not fuse with egg Division of zygote is affected Cope, 1939 Euphytica Contd… 32
- 33. Ovule with 24 HAP, synergid (SI) receiving a pollen tube Two spermatic nuclei in synergids (SI) Ovules showing a fusion of one of the spermatic nuclei with the polar nucleus Formation of the primary endosperm nucleus Endosperm nuclei Irregular development of ovule Contd…. 33
- 34. Molecular method Apricot ( Prunus armeniaca ) SI trait has been mapped in linkage group G6 Mapping population- F2 population of Start early orange x Tryintos Valanova et al., 2003 Genetics 34
- 35. 1. Hybrid production Tedious process of emasculation can be avoided Forward and reverse cross can be easily attempted if both lines are SIC Double and triple cross hybrids can be produced Significance of self incompatibility 35
- 36. Hybrids developed using SI Crop Hybrids Cauliflower Pusa Hybrid-2, Snow Queen, Snow King, White Contessa, Pusa Kartik Sankar Xiahua 6 Cabbage BRH-5, H-44, H-43, Pusa Synthetic, Meenakshi, Pusa Cabbage-1 Chinese Cabbage Hamburg-3 Raddish Pusa Chetaki, Pusa Desi, Half Red, Acc. No. 30205, Acc. No.282, Chinese Pink, BDI-689 Cocoa CCRP 8, CCRP 9, CCRP 10, CCRP 11, CCRP 12, CCRP 13, CCRP 14, CCRP 15 Mango Arka Puneet, Arka Neelkiran, Arka Anmol 36
- 37. Performance analysis of double hybrids in Brassica napus Mid parent heterosis (%) Maximum 115.66 Minimum -3.45 Average 28.91 No. of combinations with high heterosis 42 No. of combination with negative heterosis 2 Ma et al., 2009 16th Australian Research Assembly on Brassicas 37
- 38. Superior clones with SI and good general combining ability are used as parental material Seeds from all the clones will be hybrid Main disadvantage is lack of information about exact male parent Contd….. 38
- 39. Clonal gardens of cocoa in KAU S. No. Garden No. of parents No. of plants Year of planting Avg. No. of hybrid pods year-1 1 Poly clonal garden I 12 120 1989 12000 2 Polyclonal seed garden II 38 228 1993 22800 3 Biclonal seed garden 6 1243 1996 124300 4 Polyclonal seed garden III 5 100 2000 10000 5 Polyclonal seed garden IV 8 1100 2005 110000 6 Polyclonal seed garden V 7 946 2006 94600 7 Polyclonal seed garden VI 10 400 2010 40000 8 Poly clonal seed garden VII 6 286 2010 28600 9 Polyclonal seed garden VIII 8 299 2014 29900 Total 4722 472200 Minimol et al., 2015, Cashew Cocoa J. 39
- 40. 3. Certain crops like pineapple parthenocarpy along with SI results in seedless fruits Contd….. 40
- 41. 4. Plays a key role in evolution SI promotes out breeding Increase in heterozygosity and wide variability Possibility for new gene combination Contd… 41
- 42. Comparison between SI and male sterility Self-incompatibility Male sterility Hybrid seeds can be collected from both the parents if they are SI Hybrid seeds can be collected only from MS lines Maintenance is easy by bud pollination Specific maintainer line required No specific restorer line required Suitable restorer has to be identified No negative effect of sterile cytoplasm Linkage drag of sterile cytoplasm with other undesirable character 42
- 43. S. No. Parental genotype No. of grown plants No. of harvested plants Weight of harvested seeds (g) Mean weight of seeds plant-1 (g) 1 Montano (SI) X Fortuna 13 (SC) 24 22 40 1.8 2 Brilant (CMS) X Fortuna 13 (SC) 24 20 45 2.3 Comparison between SI and MS hybrids of cauliflower Kucera et al., 2006 Hortic. Sci. (Prague) Montano (SI) Brilant (CMS) 43
- 44. F1 Montano (SI) X FT 13 F1 Brilant (CMS) X FT 13 Good uniformity High curd quality Good covering of curd by inner leaves Satisfactory disease resistance Less uniform Small and lighter curds Susceptible to disease 44
- 45. Limitations in exploiting self-incompatibility • Continued selfing will lead to inbreeding depression • Continuous inbreeding may lead to complete loss of the inbred lines • Pseudo-incompatibility • Hybrid seeds would be expensive if the self-incompatible lines are difficult to maintain • Environmental factors reduce or totally overcome SI • Preferential visit of pollinating insects • Transfer of S-allele is tedious and complicated 45
- 46. Temporary suppression of SI For maintenance of inbred lines • Bud pollination • Mixed pollination • Surgical techniques – Brassica • End of season pollination • High temperature – Trifolium, Lycopersicon • Increased CO2concentration • High humidity • Salt (NaCl) sprays • Irradiation (Solanaceae) • Double pollination • Grafting (Trifolium pratense) 46
- 47. Fruit set in passion fruit after selfing S. No. Treatment No. of flowers selfing Fruit set (%) 1 Bud selfing 30 16.67 2 One selfing at anthesis (control) 30 0.00 3 Double pollination at anthesis 30 10.00 Rego and Rego, 2000 Theor. Appl. Genet. 47
- 48. Over coming self incompatibility in Chinese cabbage S. No. Lines Pollination stage No. of flowers No. of seeds SI index 1 Self- incompatible Bud 132 124 0.94 Anthesis 135 8 0.06 Anthesis with NaCl treatment 54 157 2.54 Wang et al., 2012 Plant Physiol. 48
- 49. Effect of CO2 treatment on pollen germination and fruit set in a self-incompatible cocoa genotypes Pollination treatment Pollen germination (%) Fruit set (%)CO2 Method - Self 0 0.0 - Cross 100 45.6 + Self 95 44.8 + Cross 100 38.4 Aneja and Badilla, 1994 Hortic. Sci. 49
- 50. Summary • SI is a genetic mechanism to avoid self pollination • At least two genes within S-locus control SI • Genes are multi allelic in nature • Methods to determine SI varies with the type • A viable tool for hybrid production • Many advantages over male sterility • Major limitation is production/maintenance of inbreds • Temporary methods to over come SI 50
- 51. The road ahead ….. • Need to identify and characterize precisely the S-alleles in the germplasm and utilize the strong alleles to develop stable SI parents • Efforts to be taken to transfer SI related gene and subsequent exploitation of heterosis by producing hybrid seeds 51
- 52. 52
Editor's Notes
- There are several mechanisms in nature that promote cross pollination such as Out of these SI is of special significance, because it is exploited in hybrid seed production.
- Gower has defined SI Pollen grains fail to germinate on the stigma Some times - pollen grains do germinate, pollen tube fail to enter the stigma In some species, pollen tube enter the style, but growth too slow to effect fertilization before the flower drops Some times fertilization affected, but embryos degenerate at early stage Self incompatibility appears to be a biochemical reaction, but precise nature of these reactions is not clearly understood. With this back ground let me introduce my topic
- Content included in the seminar are
- Cross pollinating species with bisexual flower have
- Nearly 6000 species in world possess this character and distributed in 250 genera from 70 families representing 19 orders of both monocots and dicots
- The classical classification of SI was given by Lewis, He classified SI into 2 main groups- Homo and Hetero Homomorphic SI again sub classified into
- Coming to the hetero SI – classification is based on the difference in the morphology of flower Referred as distily Flowers of different incompatibility groups are different in their morphology. For example in Primula, they have two types of flowers, Pin and thrum - produced on different plants The only compatible mating is between pin and thrum flowers It is governed by the locus ‘s’ Genotype of pin is homozygous recessive ‘ss’ and thrum is heterozygous ‘Ss’ The S is dominant over s. SI is governed by genotype of the parent that produce them -hence it is called heteromorphic sporophytic.
- Phenotype of the flower is Pin and thrum Pin is with-ss and Thrum Ss Pin will produce gamete with ss and thrum will produce gametes with Ss Since the reaction is sporophytic, all pollen produced by pin will behave as s and thrum as S S is dominant over s so the style of thrum will have S reaction while pin have s reaction.
- This is the mating system proposed in Heteromorphic SI Pin can cross only with thrum and thrum can cross only with pin But pin cannot cross with pin and thrum cannot cross with thrum This system is of least importance- it occurs in sweet potato and buckwheat
- Coming to the homomorphic SI here morphology of flower is nothing to do with incompatibility reaction.
- East and Mangelsdorf have given sub classification of GSI based on the No. of genes controlling SI reaction. as Mono and bifactorial. If incompatibility reaction is controlled by single gene – monofactorial More than 2 genes –bifactorial
- Pollen parent with genetic constitution S1 S2 produce two gametes S1 and S2 In female parent – the two alleles are co-dominant and both get expressed Hence when pollen grain with S1 or S2 gamete make up fall on a plant with S1 S2 both will not germinate since the reaction of stigma is codominant. When it fall on the stigma of female plant with S1S3, S2 can germinate and when it falls on the Female with S3 S4 complete incompatibility
- Where as in SSI – genotype of the parent determine si reaction. S1>S2, S2>S3, S3>S4 etc., Male gamete both S1 and S2 produced from S1S2 will behave has S1 And in style S1 S2 behave as S1 Hence cross b/w S1 S2 x S1S2, S While S1S2 with S3 S4 is compatible
- There are some crops where sporophytic SIC is reported
- With classical genetics S-locus was assumed to be a single gene but after 1987 molecular studies revealed S-locus to be much more complex The S-locus consists of at least two linked transcriptional units arranged in pairs One unit function as male determinant while other as female determinant Multigene complex at the S-locus is inherited as one segregating unit Variants of gene complex are called “S-haplotypes”
- Let us see the molecular gene action in brassicaceae SRK-determines SI reaction in stigma/style- function as female determinant, SRK- predominantly expressed in stigma papilla cells just prior to flower opening, when stigma acquires SI reaction. SRK- is a trans membrane receptor present in plasma membranes of papilla cells SP 11/SCR- is male determinant- predominantly expressed in the anther tapetum SP 11/SCR- accumulate during in the pollen coat during pollen maturation. When pollen lands on stigma- SP11(present in its coat) crosses papilla cell wall and bind SRK present in papillla plasma membrane in specific manner and causes SRK to autophosphorylation based signalling cascade- and the end result is the prevention of pollen hydration and germination/tube growth
- These are the some S-locus/ S related genes are reported in brassicaceae.
- S-Rnase is female determinant- expected exclusively in the pistil and localized in the extracellular matrix in the upper region of style and function as specific cytotoxin that inhibit the growth of incompatible pollen tubes SLF(S-locus F-box protein) or SFB(S-haplotype-specific F-box protein)- male determinant S-Rnase enter both compatible and incompatible pollen tubes. But they degrade the RNA of self ie incompatible pollen tubes only. SLF/SFB- is a member of F-box family proteins, which generally function as a component of a E3 ubiquitin ligase complex. Thus, SLF/SFB is expected to be involved in ubiquitin-mediated protein degradation of non self S-Rases.
- Only female determinant gene has been identified- named S-protein. Male determinant is unknown In SIC reaction, S protein get bind with SBP and result in increased con. Ca. - trigger various reactions, mainly actin depolymerisation resulting in death of pollen tube.
- T86
- T 63
- SI quantified based on the No. of seeds that develop to maturity after each specific self and cross pollination. Disadvantage -long period is between pollination and seed maturity, subsequent expression of compatibility and incompatibility and seeds developing and reaching maturity may be affected by diseases, water shortage, high temp. and other stresses – seed count is not reliable method Fluorescent microscope-12-15 hours. Pollinated flowers are collected, excised ovaries are softened in 60% NaOH and placed in aniline blue for staining. After 48 hours of pollination- stigma and style are squashed on microscope slide- aniline blue accumulates on the pollen tube and florescence when irradiated with ultra violet light.- hence with appropriate light filters under a fluorescent microscope, the tubes are visible and the background of stylar region is unseen. Penetration of tube indicate the compatibility and non penetration of tube- SI.
- Varies with type of self incomp. Stigma and style are squashed on microscope slide after 48 hr of pollination Alinine blue- stain Fluoresces when irradiated with UV light
- This slide - behaviour of pollen nuclei in SI reaction. V photho- fusion b/w sperm and egg is not affected – resulted in irregular ovule.
- Pollination studies and cytological studies are further validated by molecular studies. Markers associated with self incompatibility trait has been identified in many crops. In a study conducted by Valanova and co workers in Apricot they were able to map SI trait in linkage group G6 The Mapping population used for the study was F2 derived by selfing F 1 obtained by crossing two varities Start early orange x Tryintos
- S-1300 B. napus SI line and 44 B. napus SC lines, which are restorers of S-1300 were used in the study. S-1300 was crossed with restorers to obtain F1 hybrids. The average heterosis of 28.91% indicate hybrids have high mid parent heterosis
- The yield of F1 seeds in hybridization experiment based on SI was 1.8 grams per plant of SI mother line. In hybridization based on CMS, the yield of F1 seeds per CMS plant was 2.3 grams. The F1 hybrid of SI line Montano × self-pollinating line from cv. Fortuna showed to be the best combination in a preliminary field trial.
- (effect of NaCl on overcoming self incompatibility in non-heading chinese cabbage(Brassica campestris sp. chinensis) studied by fluorescent microscopy
- Till date we