ISBN: 3-540-65217-5
TITLE: Incompatibility and Incongruity in Wild and Cultivated Plants
AUTHOR: Nettancourt, Dreux de
TOC:

1 The Basic Features of Self-Incompatibility 1
1.1 A Definition 1
1.2 Nature of the SI Reaction 2
1.3 Classification of SI Systems 3
1.3.1 The Time of Gene Action in the Pistil 3
1.3.2 The Time of Gene Action in the Stamen 4
1.3.2.1 Determination of the Pollen Phenotype in Gametophytic Systems 4
1.3.2.2 Determination of the Pollen Phenotype in Sporophytic Systems 6
1.3.3 The Association with Floral Polymorphism 7
1.3.3.1 The Distylic Condition 8
1.3.3.2 Tristyly 9
1.3.4 The Site of Gene Expression 10
1.3.4.1 Stigmatic Inhibition 10
1.3.4.2 Stylar Inhibition 11
1.3.4.3 Ovarian Inhibition 12
1.3.5 The Number of Genetic Loci and the Involvement of Polyallelic Series 13
1.3.5.1 The Genetic Basis of Recognition 13
1.3.5.1.1 Control by a Single but Complex Locus 13
1.3.5.1.2 Recognition by Two Unlinked Loci in the Grasses 14
1.3.5.1.3 Recognition by Two or More Loci in Several Other Families 14
1.3.5.2 Polyallelism at the Incompatibility Loci 14
1.3.5.3 How Many Genes are Involved in the Rejection Process? 15
1.3.5.3.1 Stigmatic SSI 15
1.3.5.3.2 Stigmatic GSI 15
1.3.5.3.3 Stylar GSI 15
1.4 Recapitulation on the Classification of SI Systems 16
1.5 The Distribution of SI Systems in the Angiosperms 17
1.5.1 Incidence of SI in the Families of Flowering Plants 17
1.5.2 Distribution of SI among Species Important for Agriculture 21
1.6 Chronology of Early Researches on SI 23
2 The Genetics of Self-Incompatibility 25
2.1 Sporophytic Heteromorphic Systems 25
2.1.1 Distyly 25
2.1.1.1 A Supergene 26
2.1.1.2 ...Within Which Recombination Occurs 27
2.1.1.3 The Supergene is Controlled by Modifier Genes 28
2.1.2 Tristyly 28
2.1.2.1 Homomorphic Variants and Supergenes in Tristyly 30
2.1.2.2 One Genotype, Two Phenotypes 30
2.1.2.3 Dominance Change in O. articula 30
2.1.2.4 Breeding Behavior Can be Independent of Floral Heteromorphism 31
2.1.3 Multi-Allelic Series in Species with Incomplete Heterostyly? 31
2.2 Sporophytic Homomorphic Stigmatic Control 31
2.2.1 Two Di-Allelic Loci 31
2.2.2 A Single Locus with Polyallelic Series, Dominance and Competitive Interaction: the Brassica Type 32
2.2.2.1 The Brassica Haplotypes 34
2.2.2.1.1 Class-I Haplotypes 35
2.2.2.1.2 Class-II Haplotypes 35
2.2.2.2 Extension of the Haplotype Concept to Other Genes, Other Families and Other Systems 36
2.2.2.3 S-Locus-Related(SLR) Genes in Brassica 37
2.2.2.4 Many Genes in the S-Linkage Group 37
2.2.3 A Single Sporophytic Stigmatic Locus with Multiple Alleles but without Dominance and Competitive Interaction 38
2.2.4 Three or Four Polyallelic Loci in Eruca sativa 38
2.3 Gametophytic Homomorphic S Systems with Polyallelic Series 39
2.3.1 One-Locus Stigmatic Control: the Case of the Style-Less FieldPoppy 39
2.3.1.1 Genetics of SI Polymorphism in P. rhoeas and Other Species with Polyallelic, Monofactorial SI 40
2.3.1.2 The Number of S Alleles in P. rhoeas 42
2.3.2 Two Loci-Stigmatic Control in the Grasses 42
2.3.2.1 Breeding Efficiency of the SZ System 43
2.3.2.2 The Size of Polyallelic Series 43
2.3.3 Four-Loci Stigmatic Gametophytic Control in the Ranunculaceae, the Chenopodiaceae and the Liliaceae 45
2.3.3.1 Few Alleles per Locus in Tetra-Factorial Stigmatic GSI 46
2.3.3.2 Linkage Between the Four SI Genes 47
2.3.3.3 SI is Maintainedin TetraploidR. repens 47
2.3.4 Monofactorial Stylar GSI with Polyallelic Series 47
2.3.4.1 The Size of Polyallelic Series in Stylar Monofactorial GSI 48
2.3.4.2 The Structure of the S Locus in Stylar Monofactorial GSI 49
2.3.4.3 Identification of S-Bearing Chromosomes 50
2.3.5 Bifactorial Stylar GSI with Epistatic Relationships 50
2.3.6 Three or Four S Loci in a Complementary System of Lotus tenuis 52
2.3.7 Ovarian Gametophytic SI 52
2.3.7.1 Post-Zygotic OSI? 53
2.3.7.2 Cyclic, Post-Zygotic, Polygenic SI 54
2.3.7.3 Incompatible Pollen Tubes That Prevent Ovule Development 54
2.4 Sporophytic-Gametophytic Systems 55
2.4.1 Three Genes Participate in the Ovarian Gametophytic-Sporophytic System of Theobroma cacao 55
2.4.2 Sporophytic Stigmatic SI Revisited in the Cruciferae and the Compositae 56
2.4.3 A One-Locus Sporophytic System with Traces of Gametophytic Pollen Control in the Caryophyllaceae 58
2.5 Genes Involved in the Rejection Phase of SI 59
2.5.1 In Stigmatic SI Systems 59
2.5.2 The Rejection Phase in Species with Stylar GSI 61
2.5.3 SI in the Ovary 61
2.6 SI in Polyploids 62
2.7 Equilibrium Frequencies of SI Alleles 62
2.7.1 Two Alleles at One Locus in a Sporophytic System 62
2.7.2 Trimorphism 63
2.7.3 One Polyallelic Locus in a Sporophytic System 63
2.7.4 Polyallelic Series in a Monofactorial Gametophytic System 64
2.7.5 Two Polyallelic Gametophytic Loci 64
2.7.6 The Number of Possible Allelic Combinations in Theobroma 65
2.8 The Maintenance and Efficiency of Incompatibility Systems 65
2.8.1 Population Sizes and Numbers of Incompatibility Alleles 66
2.8.1.1 Smallest Numbers of Alleles Required 66
2.8.1.2 "Molecular Restraints to the Coding Capacity of the S Gene in Papaver"? 66
2.8.1.3 Consequences of High Numbers of Alleles at the SI Loci 67
2.8.1.4 Linkage Effect as a Main Cause to Unequal S-Allele Frequencies in British Populations of P. rhoeas 67
2.8.2 The Selection of Rare Alleles and Replacement Processes 67
2.8.3 Explanations to the Large Numbers of Alleles Foundin Oenothera, Trifolium, Carthamus and Lolium 68
2.8.3.1 High Mutation Rates 68
2.8.3.2 Subdivisions of Populations 69
2.8.3.3 Migration and Hard Seed Carryover 69
2.8.4 The Efficiency of SI Mechanisms for Preventing Unions Between Near Relatives 70
2.8.4.1 A Comparison of Parent-Offspring Relationships in Heterostylic and Gametophytic Systems 70
2.8.5 Effects of Pollen and SeedDispersal, Overlapping Generations and Plant-Size Variations in Populations at Equilibrium 71
2.8.6 A New Mathematical Approach to SI Polymorphism in a One-Locus Gametophytic System 71
2.8.7 The Concept of a Frequency-Equivalent Population 72
3 Cellular and Molecular Biology of Self-Incompatibility 73
3.1 Heteromorphic Incompatibility 74
3.1.1 A System of Its Own 74
3.1.1.1 The Research Approaches are Different 74
3.1.1.2 Several Rejection Sites 74
3.1.1.3 Rejection Cascades 75
3.1.1.4 Stigmatic Rejection May Occur on Wet Stigmas 76
3.1.1.5 The Rejection Sites Are Not Always Typical of a Sporophytic System 76
3.1.1.6 The Incompatibility Loci Are Usually Di-Allelic 76
3.1.1.7 Role of the Internal Environment in the Specificity of Incompatibility Products 77
3.1.2 Occurrence and Function of Stigma and Pollen Polymorphism 78
3.1.2.1 Analyses of Pollen Walls 79
3.1.2.2 The Role of Pollen and stigma Dimorphism on Pollen Affixation and Pollen Metabolism 81
3.1.2.2.1 Effects of Differences in the Morphology of the Stigmatic Cuticle and in the Sculpturing of Pollen Exine 81
3.1.2.2.2 Function of the Pollen Exine in Jepsonia 83
3.1.2.2.3 Availability of Exudate on the Stigma Surface 83
3.1.2.2.4 Variations in Osmotic Pressures 83
3.1.3 The Molecular Biology of Heteromorphic SI 84
3.1.3.1 Identification of S-Recognition Factors 84
3.1.3.2 Is There a Fundamental Difference Between SI in Heteromorphic Species and SI in Sporophytic-Homomorphic Systems? 85
3.2 Homomorphic Sporophytic Stigmatic SI: the Brassica Type 87
3.2.1 Morphology and Structure of Stigma and Pollen Surfaces 87
3.2.1.1 The Stigma Surface 87
3.2.1.2 The Pollen Exine and the Pollen Coating 88
3.2.1.2.1 Differences in the Pollen Exine Sculpturing Between SSI and GSI 89
3.2.2 The Route of the Compatible Pollen Tube Through the Stigma 89
3.2.2.1 Self-Incompatible Brassica oleracea 89
3.2.2.2 Self-Compatible Arabidopsis thaliana 90
3.2.3 Stigmatic Proteins Involvedin the Recognition of Incompatible Pollen 91
3.2.3.1 Immunological Detection and Purification of SLG 91
3.2.3.1.1 Purification of SLG 92
3.2.3.2 Essential Features of SLG 92
3.2.3.2.1 Cloning of the Gene Encoding SLG 92
3.2.3.2.2 The SLG Sequence 93
3.2.3.2.3 Structure of SLG and Homologies Between Alleles 94
3.2.3.2.4 Nature, Origin and Frequency of Sequence Variations Between Different Alleles 94
3.2.3.2.5 Co-Evolution of SLG and SRK 94
3.2.3.2.6 Structural and Functional Distinctness of SLG in Class-II Haplotypes 95
3.2.3.3 The S-Receptor Kinase Gene, SRK 95
3.2.3.3.1 Essential Features of SRK 96
3.2.3.4 A Direct Method for the Cloning of S Haplotypes 98
3.2.3.5 SLG and SRK Are Present, Often as Traces, in Other Parts of the Brassica and Transgenic Nicotiana Flowers 99
3.2.3.5.1 In the Pollen 99
3.2.3.5.2 In Anther Walls 99
3.2.3.5.3 In the Transmitting Tissue of the Stigma, Style and Ovary 99
3.2.3.5.4 In Transgenic Tobacco 99
3.2.3.6 A Putative Receptor Kinase Gene in Ipomoea trifida 99
3.2.3.7 SLG and SRK Have Many Relatives 100
3.2.3.7.1 Members of the S Multi-Gene Family That Are Linked to the S Locus 101
3.2.3.7.2 S-Locus-RelatedSequences in Arabidopsis 102
3.2.3.7.3 Relationship of SRK/SLG to the Putative Kinase Receptor (ZmPK1) from Maize 102
3.2.3.7.4 ARC1, a Putative Downstream Effector for SRK 102
3.2.4 The S-Specific Pollen Determinant 102
3.2.4.1 ExpectedFeatures of the S Determinants 102
3.2.4.1.1 Allelism to the SRK or SLG Genes? 102
3.2.4.1.2 Likelihoodof a Dimer Mechanism in SI Systems of the Brassica Type 103
3.2.4.1.3 Linkage of Pollen and Stigma Determinants to the S Haplotype 103
3.2.4.1.4 Sporophytic Expression 104
3.2.4.2 Contribution of the Tapetum to the Pollen Coat and to SI 104
3.2.4.2.1 Contribution to Pollen Coating 104
3.2.4.2.2 Evidence That the Pollen Coating Carries the Pollen S Determinant 104
3.2.4.2.3 Tapetal Origin of Pollen S Determinants? 105
3.2.4.3 The Search for the Pollen S Determinant: Recent History 105
3.2.4.3.1 The S-Glycoprotein-Like Anther Protein 106
3.2.4.3.2 The S-Locus Anther 106
3.2.4.3.3 Pollen-Coat Protein Class A 106
3.2.4.3.4 Pollen-Coat Protein A2 107
3.2.4.3.5 SLL2-S9 and S-Locus Anther-Expressed S9 Gene 107
3.2.4.3.6 The Systematic Analysis of S and S-Related Regions 107
3.2.4.4 Finding the Pollen Determinant 108
3.2.4.4.1 The Gene Fulfils the Requirements for the Hypothesized Pollen Determinant 108
3.2.4.4.2 SCR Is a Relative of PCPs 108
3.2.4.4.3 Origin (Sporophytic and Tapetal) of SCR 108
3.2.5 What Happens After an Incompatible Pollination? 109
3.2.5.1 Pollen Capture by the Stigma 109
3.2.5.2 Relationships Between Pollen Hydration and SI 110
3.2.5.3 Stigmatic S Glycoproteins Are Glycosylated. 110
3.2.5.4 The Recognition of Incompatible Pollen 110
3.2.5.5 Rejection of Incompatible Pollen 112
3.2.5.6 The Role of Callose 112
3.3 Stigmatic Monofactorial Multiallelic GSI in Papaver rhoeas 113
3.3.1 Compatible and Incompatible Pollinations 113
3.3.1.1 Morphology and Growth of Compatible Pollen Tubes 113
3.3.1.2 Incompatible Pollen Grains and Pollen Tubes 113
3.3.2 An In Vitro Bioassay for the Study of Stigmatic S Proteins  Pollen Metabolism and Pollen-Stigma Interactions after Self-Pollination 114
3.3.3 Characterization of Stigmatic S Proteins and Cloning of the Stigmatic S Gene 114
3.3.3.1 Isolation and Characterization of the Stigmatic S Proteins 114
3.3.3.1.1 Isolation and Testing of Function 114
3.3.3.1.2 Co-Segregation with S Alleles 114
3.3.3.1.3 Characteristics of the Protein 115
3.3.3.1.4 S Activity, S Specificity and the Role of Glycosylation 115
3.3.3.1.5 Polymorphism of S Sequences 115
3.3.3.1.6 The S Proteins Are Not Major Proteins of the Stigma 115
3.3.3.1.7 The S Protein Is Not a Ribonuclease 116
3.3.3.2 Cloning and Nucleotide Sequencing of the Stigmatic S Gene 116
3.3.3.3 Biological Activity of Mutant Derivatives of the S Protein 116
3.3.3.4 Large Numbers of ORFs with Homology to the Stigmatic S Gene of Papaver Are Present in the Arabidopsis Genome 117
3.3.4 Pollen Genes That Participate in the SI Response 117
3.3.4.1 Inhibition of Incompatible Pollen Tubes Depends on Pollen-Gene Expression 117
3.3.4.2 Involvement of a Signal-Transduction Mechanism in the SI Response 118
3.3.4.3 A Membrane Glycoprotein That Binds Stigmatic S Proteins in Pollen 119
3.3.4.4 ProgrammedCell Death Is the End Point of the SI Response in Papaver rhoeas 121
3.4 Stigmatic Bi-Factorial GSI in the Grasses 121
3.4.1 Flowers and Pollination 122
3.4.1.1 Stigma and Pollen 122
3.4.1.2 Compatible Pollination 122
3.4.1.3 Self-Pollination 122
3.4.2 SI in Phalaris coerulescens 123
3.4.2.1 Identification of Restriction Fragments
Linked to the Pollen S Gene 123
3.4.2.2 Bm2 is not the S Gene 123
3.4.2.3 Involvement of Thioredoxins in the SI Mechanism? 124
3.4.3 SI in Rye 125
3.4.3.1 Evidence that the SI Mechanism Involves Phosphorylation and Is Ca^{2+} Dependent 125
3.4.3.1.1 In Situ Pollen Phosphorylation 125
3.4.3.1.2 Gel Electrophoresis of Pollen Phosphoproteins 125
3.4.3.1.3 Effects of Inhibitors 126
3.4.3.2 A Model for the SI Mechanism in Rye 126 
3.4.4 Applicability of the Model to All SI Species of Grasses 127
3.4.4.1 The S and Z Loci Are Not Interchangeable 127
3.4.4.2 ConservedS Sequences of Brassica Amplify S-Linked Fragments in Rye 127
3.5 Monofactorial Stylar GSI with Multiple Alleles: the Nicotiana Type 128
3.5.1 Pollen-tube Morphology and Growth in Compatible Styles 128
3.5.1.1 Observation under the Light Microscope 128
3.5.1.1.1 Role and Specificity of the Stigmatic Exudate 129
3.5.1.1.2 Mitosis in the Generative Nucleus of Petunia hybrida 129
3.5.1.2 Electron Microscopy 129
3.5.2 Morphology and Growth of Incompatible Tubes 130
3.5.2.1 Incompatible Tubes of N. alata under Epifluorescence Illumination 130
3.5.2.2 Electron Microscopy 131
3.5.2.3 The Role of Callose 132
3.5.2.4 Mitosis in the Generative Nucleus of P. hybrida 132
3.5.3 Early Research on the Nature of the SI Reaction 133
3.5.3.1 SI as a Process of Growth Inhibition 133
3.5.3.2 Is the S Phenotype of Mature Styles Determined before Pollination? 133
3.5.3.2.1 Evidence from In Vitro Tests 133
3.5.3.2.2 Diverging Results 133
3.5.3.3 First Models of the Gametophytic Stylar SI Mechanism 134
3.5.3.4 Towards the Detection of Stylar S Proteins 135
3.5.4 Isolation, Cloning and Sequencing of a Stylar Protein Segregating with the S2 Allele of N. alata 136
3.5.5 The S-AssociatedGlycoproteins Are Ribonucleases, and SI Involves the Degradation of Pollen RNA 137
3.5.6 Evidence that the S Proteins of Petunia and Nicotiana Are Responsible for the S-Allele- Specific Recognition and Rejection of Self Pollen 138
3.5.6.1 Induction of Loss and Gain of Functions at the S Locus of P. inflata 138
3.5.6.2 S-Allele-Specific Pollen-Tube Rejection in Transgenic Nicotiana 139
3.5.6.3 Proof that Ribonuclease Is Involved in the Rejection of Self Pollen 139
3.5.7 Main Features of the S-Ribonuclease Gene and of Ribonucleases 139
3.5.7.1 Distribution and Structural Features of the Gene 139
3.5.7.1.1 Solanaceae 140
3.5.7.1.2 Rosaceae 141
3.5.7.1.3 Scrophulariaceae 141
3.5.7.2 What Are the Effects of S Ribonucleases on rRNA and mRNA? 141
3.5.7.3 Are the Effects of Ribonucleases Irreversible? 142
3.5.7.4 Why Pollen Tubes Are Not Inhibited in the Stigma 143
3.5.7.5 What Determines the S Specificity of Stylar Ribonucleases? 143
3.5.7.5.1 The Role of the Carbohydrate Moiety 143
3.5.7.5.2 The Role of HV Regions 144
3.5.8 S-Gene Products in Pollen Grains and Pollen-Pistil Recognition 145
3.5.8.1 The S-Ribonuclease Gene Is Expressed in Developing Pollen Grains 145
3.5.8.1.1 N. alata 145
3.5.8.1.2 P. hybrida 145
3.5.8.1.3 L. peruvianum 145
3.5.8.2 ...but Pollen S Ribonucleases Do Not Determine the Pollen S Phenotype 145
3.5.8.3 Involvement of Protein Kinase? 146
3.5.8.3.1 A Pollen Receptor-Like Kinase 1 in P. inflata 146
3.5.8.3.2 In Vitro Phosphorylation of the S Ribonucleases from N. alata 147
3.5.8.4 The Role of Pollen Determinants 147
3.5.8.5 Current Research Regarding the Identification of Pollen S Determinants 149
3.5.8.5.1 A Functional Genome Approach to Search for the Pollen S Gene of P. inflata 149
3.5.8.5.2 Towards the Fine-Scale Mapping of the S Locus in Petunia hybrida 149
3.5.8.5.3 Use of a Two-HybridSystem to Identify the Pollen S Component in S. chacoense 149
4 Breakdown of the Self-Incompatibility Character, S Mutations and the Evolution of Self-Incompatible Systems 151
4.1 The Physiological Breakdown of SI 152
4.1.1 Age Factors 152
4.1.1.1 Bud Pollination 152
4.1.1.2 Delayed Pollination, Use of Stored Pollen and End-of-Season Effects 153
4.1.2 Irradiation 153
4.1.2.1 Chronic Exposure to Low Dose Rates of Radiation 154
4.1.2.2 Acute Irradiation of Styles 154
4.1.2.3 High Temperatures 155
4.1.3 Application of CO2 156
4.1.4 Hormones and Inhibitors 156
4.1.4.1 alpha-Naphthalene Acetic Acid and Indole Acetic Acid 156
4.1.4.2 Effects of Transcription and Translation Inhibitors 157
4.1.4.3 Effects of Proteinase and Tunicamycin 158
4.1.4.4 Effects of Inhibitors of Protein Phosphatase 158
4.1.5 Pistil Grafting 159
4.1.6 Mutilations, Injections and the Effects of Castration on Pollen-Tube Growth 159
4.1.7 Mentor Effects 160
4.1.7.1 Mentor Pollen Is More Efficient When Inactivatedor Killed 160
4.1.7.2 Nature of the Mentor Effects 161
4.2 Genetic Breakdown of SI and S-Gene Mutations 161
4.2.1 Loss of S Function in Pollen Grains of Species with SSI 161
4.2.2 Loss of S Function in the Pollen of Species with GSI 163
4.2.2.1 Function Loss of the Pollen Determinant Associatedwith the Presence of a Free Centric Fragment 163
4.2.2.1.1 Competitive Interaction 163
4.2.2.1.2 Complementation 165
4.2.2.1.3 Restitution 165
4.2.2.1.4 Likelihoodof the Three Hypotheses 166
4.2.2.1.5 Origin of the Centric Fragment in "Pollen-Part" SC Mutants of N. alata 166
4.2.2.1.6 Current Approaches to the Biomolecular Study of PPMs Associated with Additional Chromosomal Material 166
4.2.2.2 Function Loss of the Pollen Determinant Not Associatedwith the Presence of a Centric Fragment 168
4.2.2.3 The Frequency of S Mutations Leading to the Loss of SI Function in Pollen Grains 169
4.2.2.4 Production of Cultivars with Modified Breeding Regimes: Examples of Traditional and Molecular Approaches 170
4.2.2.4.1 Cherry Stella 170
4.2.2.4.2 Elstar 170
4.2.2.5 The Use of "Pollen-Part" Mutations for the Prod uction of F1 Hybrid Seed 171
4.2.3 Loss of S Function in the Stigmas of Species with SSI 172
4.2.3.1 Utility of SC Stylar Mutations and of Silencing Studies for the Understanding and Exploitation of SI 172
4.2.3.1.1 Breakdown of SI Through Silencing Effects 172
4.2.3.1.2 Why Gene Silencing Occurs 173
4.2.3.1.3 Scientific Interest of S-Gene Silencing 173
4.2.3.1.4 The Importance of Specific S-Function Losses for Basic and AppliedResearch 174
4.2.4 Loss and Gain of S-Function Approaches in the Stigma or Style of Species with GSI 174
4.2.4.1 SC Mutants Arising Spontaneously or from Conventional Mutagenic Treatment 174
4.2.4.2 Genetic Constructs and Ablations of S-Gene Products Leading to SC and their Importance for SI Research 175
4.2.4.2.1 How to Induce Function Loss Through the Use of Anti-Sense DNA 175
4.2.4.2.2 Loss of Function and Gain of Function Approaches Are Complementary 176
4.2.4.2.3 Competition Effects Occurring in the Styles of Petunia Plants with a Tri-Allelic S2S3S3Genotype 177
4.2.4.3 Presence and Expression of S Ribonucleases in Self-Compatible Lines 177
4.2.4.4 Loss and Gain of Function in the Pollen of Plants with Mono-Factorial Stylar GSI 178
4.2.5 SC Through Genetic Changes Occurring Outside the S Locus 178
4.2.5.1 In Sporophytic Systems 179
4.2.5.2 In Gametophytic Systems 180
4.2.5.2.1 Mutations of Major Genes 180
4.2.5.2.2 Action of Polygenes 180
4.2.5.2.3 S Alleles Trappedin Translocation Rings 181
4.2.6 SC in Polyploids 182
4.2.6.1 TetraploidForms and TetraploidSpecies Are Often Self-Compatible 182
4.2.6.2 Competitive Interaction in Diploid Hetero-Allelic Pollen 182
4.2.6.3 Effects of Polyploidy on SI in Monocots and Certain Primitive Dicots 183
4.2.7 The Generation of New SI Alleles 184
4.2.7.1 Conflicting Evidence Regarding the Role of HV Regions in the Solanaceae? 184
4.2.7.1.1 Only Four AAs Are Responsible for the Difference in Specificity Between the S11 and S13 Alleles of Solanum chacoense 184
4.2.7.1.2 In Petunia and Nicotiana, the Ribonuclease Sequences Responsible for Pollen Recognition Appear to be Scattered Throughout the Molecule 185
4.2.7.2 New S Alleles Appear in Inbred Populations 187
4.2.7.3 Origin of New Specifities 188
4.2.7.4 The Dual Specificity of New S Alleles May Play a Key Role in the Generation of New S Alleles 188
4.2.7.5 The Role of the Genetic Background 189
4.2.7.6 Methods for a Rapid and Reliable Identification of S Alleles in Plant Breeding 189
4.3 Evolution of SI 190
4.3.1 Allelic Diversity 190
4.3.1.1 Origin, Distribution and Extent of Divergences among Functional S Alleles in the GSI System of the Solanaceae 191
4.3.1.1.1 Intragenic Crossing-Over or Accumulation of Single BP Changes? 191
4.3.1.1.2 Distribution and Variability of S Alleles 192
4.3.1.1.3 Inter-Species Variation in S-Allele Age and Number 192
4.3.1.2 S Alleles in Other Families with a Ribonuclease GSI System 192
4.3.1.2.1 Differences Between the Scrophulariaceae and the Solanaceae 192
4.3.1.2.2 Differences Between the Rosaceae and the Solanaceae 193
4.3.1.2.3 S-RNase Polymorphism in the Rosaceae 193
4.3.1.3 Homology or Convergence Among S Ribonucleases? 193
4.3.1.3.1 What Happens in Legumes? 194
4.3.1.4 SLG and SRK Allelic Divergences in the Brassicaceae 194
4.3.1.4.1 Hyper-Mutability of the S Locus 194
4.3.1.4.2 The S Locus is not a Hot Spot of Recombination 195
4.3.1.4.3 Distribution and Extent of Variations Between S Alleles 196
4.3.1.4.4 Extent of the Divergence Between SLG and SRK of a Same S Haplotype 197
4.3.1.4.5 How is Sequence Similarity Usually Maintained Between SRK and SLG in Brassica Haplotypes? 197
4.3.1.5 S Alleles Are Very Old 197
4.3.1.5.1 S-Ribonuclease Polymorphism in the Solanaceae Arose Before the Emergence of Nicotiana, Petunia and Solanum 198
4.3.1.5.2 The Origin of SLG and SRK 199
4.3.1.6 PCR Methods for Assessing Divergence Among S Alleles 201
4.3.1.6.1 In the Crucifers 201
4.3.1.6.2 In Solanaceous Species 201
4.3.2 The Multiple Origins of SI Systems 202
4.3.2.1 Early Views 202
4.3.2.1.1 SI is a Primitive Outbreeding Mechanism That Promoted the Expansion of Angiosperms 202
4.3.2.1.2 Gametophytic Poly-Allelic Incompatibility Is the Ancestral System and Occurred Only Once 203
4.3.2.2 Current Thoughts 203
4.3.2.2.1 Towards a General Agreement Regarding the Multiple Origins of SI 203
4.3.2.2.2 Multiple Gene Systems as an Origin of Mono-Factorial GSI? 204
4.3.2.2.3 S Ribonucleases CouldBe Operating in a Very Vast Majority of Species from the Dicot Families 205
4.3.3 Origin of the Different Homomorphic SI Systems and Their Relationships 206
4.3.3.1 Origin of Stylar Mono-Factorial GSI and Properties of Allelic Genealogies at the GSI Locus 206
4.3.3.2 The Origin of SSI 207
4.3.3.3 Evolution of Inbreeding Depression and Its Importance for S-Allele Invasion 207
4.3.3.4 Transitions Between GSI and SSI 207
4.3.3.5 Co-Existence of SI and SC Alleles or Breakdown of the System? 208
4.3.4 The Origin of Heteromorphic Incompatibility 208
4.3.4.1 Arguments against Evolutionary Relationships with Homomorphic SI 209
4.3.4.1.1 Homomorphic SI Systems Probably Have Multiple Origins 209
4.3.4.1.2 Heteromorphic Incompatibility is ScatteredAmong the Angiosperms and Has Poly-Phyletic Origins 209
4.3.4.1.3 There Are Basic Differences Between Heteromorphic and Homomorphic SI 209
4.3.4.2 Which Came First, Heteromorphy or Incompatibility? 210
4.3.4.3 Evolution of Tristyly 211
4.3.4.4 The Evolutionary Breakdown or Transformation of Heteromorphy 211
4.3.5 SC as the "Paradox of Evolution" 212
4.3.5.1 The DerivedCondition of SC 212
4.3.5.1.1 More Recent Arguments 213
4.3.5.2 Reasons for the Expansion of Self-Fertilizers 213
4.3.5.2.1 Outbreeding is not Always Essential Once the Environment has been Captured. 214
4.3.5.2.2 Inbreeding-Outbreeding Alternations Provide Fertility Insurance 214
4.3.5.2.3 SC Facilitates the Establishment of Colonies after the Long-Distance Dispersal of Single Seeds 214
4.3.5.2.4 Self-Fertilizers Are QualifiedColonizers 214
4.3.5.2.5 Inbred Populations Display High Levels of Genetic Diversity 215
4.3.6 The Origin of Inter-Species Incompatibility 215
5 Incompatibility and Incongruity Barriers Between Different Species 217
5.1 Inter-Species Incompatibility Under the Control of the S Locus 217
5.1.1 The SISC Rule 217
5.1.1.1 Distribution of the Barrier 218
5.1.1.1.1 In the Solanaceae 218
5.1.1.1.2 In Sporophytic Systems 218
5.1.1.1.3 The SISC Rule in the Grasses 219
5.1.2 Many Exceptions to the SISC Rule 219
5.1.2.1 They Occur Essentially in the Case of SISI Pollination 219
5.1.2.2 SI"Sc" Crosses 220
5.1.3 Differences Between the SI Reaction and Inter-Species Rejection Processes 221
5.1.3.1 Situation in the Solanaceae 221
5.1.3.1.1 Observations with the Light Microscope 221
5.1.3.1.2 Electron Microscopy 222
5.1.3.2 In the Brassicaceae 222
5.1.4 The Involvement of the S Locus 224
5.1.4.1 Unilateral Pre-Zygotic Isolation Is an Active Process in Brassica 224
5.1.4.2 SF, a Class of S Alleles That Clearly Display a Dual Function 224
5.1.4.3 Unilateral Pre-Zygotic Isolation Requires the Action of S-Ribonucleases in Nicotiana 225
5.1.5 S-Recognition Structures Participating in Inter-Species UI 227
5.1.5.1 The Antigen-Antibody Model 228
5.1.5.1.1 SISI Crosses 228
5.1.5.1.2 SISc Crosses and ScSC Crosses 228
5.1.5.1.3 Actuality of the Model 229
5.1.5.2 The "Area Hypothesis" 229
5.1.5.3 The S Locus as a Cluster of Primary and Secondary Specificities 230
5.1.5.4 Why SISI Crosses Often Fail to Follow the SISC Rule 231
5.1.6 Other Genetic Loci Also Participate in Inter-Species Incompatibility 232
5.1.6.1 The R Locus of Solanum 232
5.1.6.2 A Switch Gene in Lycopersicum 232
5.1.6.3 The Two-Power Competition Hypothesis 234
5.1.6.4 Non-Functional and "Conditionally" Functional S Alleles in a SC Cultivar of Petunia 234
5.1.6.5 An Interaction Between the S Locus and Major Genes in Lycopersicum pennellii? 235
5.2 Incongruity Between the Pollen and Pistil 236
5.2.1 What is Incongruity? 236
5.2.1.1 When Does it Start? 236
5.2.1.2 When Does it End? 237
5.2.2 Genetic Basis of Incongruity 238
5.2.3 Origin of Tissues and Genomes Involved in Incongruity 239
5.2.4 Justification of the Hypothesis 240
5.2.4.1 Arguments in Support of the Hypothesis 240
5.2.4.1.1 PollenPistil Barriers Between SC Species 241
5.2.4.1.2 The Conditions that Overcome SI Often Have No Effect on Incongruity 241
5.2.4.1.3 The Genetics of Acceptance and Non-Acceptance 241
5.2.4.2 Questions Remain 242
5.3 The Removal of PollenPistil Barriers Between Species 243
5.3.1 Intra-Species Inbreeding 244
5.3.2 Induced Mutations 245
5.3.3 Effects of Mentor Pollen 246
5.3.3.1 Can Mentor Effects on Self Pollen Consolidate Reproductive Barriers Between Species? 246
5.3.3.2 Nature of the Mentor Effects 246
5.3.4 BudPollination and the Action of Protein Inhibitors 247
5.4 Transfer of the S Gene to Autogamous Species 247
5.4.1 Introduction of the Brassica SLG and SRK Genes in SC Species 248
5.4.1.1 Transfer of SLG to B. napus 248
5.4.1.2 Transfer of SLG and SRK to A. thaliana and N. tabacum 248
5.4.2 Transfer and Expression of the S-Ribonuclease Gene in SC Species and SC Inter-Species Hybrids of Nicotiana 249
5.4.3 Other Genes ShouldBe Transferred with the S Gene 250
5.5 Reconstruction of Multigenic SI in SC Species 250
5.6 Crop Improvement Through the Transfer of Individual Genes 251
6 Conclusions 253
6.1 High-Quality Research and Abundance of Achievements 253
6.1.1 High-Quality Research 253
6.1.2 An Abundance of Achievements: Classification, Distribution and Inheritance of Self-Incompatible Systems 253
6.1.3 Fine-Structure Studies of Pollen and Pollen Tubes in Compatible and Incompatible Surroundings 254
6.1.4 Identification of S Genes Active in the Pistil 254
6.1.5 Discovery of a Putative Pollen Determinant in the Cabbage Family 254
6.1.6 Progress Towards the Understanding of S Specificity 254
6.1.7 Advances in Cellular and Molecular Surgery 255
6.1.8 New Information Regarding the Evolution of SI Systems 255
6.1.9 Bypassing Pre-Zygotic Inter-Species Barriers 256
6.2 There Are Still Numerous Gaps in Our Knowledge and Skill 256
6.2.1 Unraveling the S-Gene Family 256
6.2.1.1 Genetic Control is More Complex Than Expected 256
6.2.1.2 The S-Gene Family of Brassica is Surprisingly Large 257
6.2.1.3 S-Locus Complexity Has Also Been Found in the Solanaceae 257
6.2.1.4 The S Alleles of Papaver May Also Belong to a Large Family 257
6.2.2 Analysis of Recognition and Rejection 257
6.2.2.1 Identification and Function of S and S-Related Proteins in the Pistil 257
6.2.2.2 The Search for Pollen Determinants 258
6.2.2.3 Identification of the Genes and Processes Affectedby the Rejection Phase of SI 258
6.2.3 The Molecular Biology of SI in Heteromorphic Species 259
6.2.4 Barriers to the Expression of TransferredGenes 259
6.2.5 Evolution of SI 260
6.2.5.1 The Multiple Origin of Homomorphic SI 260
6.2.5.2 A Relationship Between GSI and Sporophytic SI? 260
6.2.5.3 A Multiple Gene System as the Starting Point for GSI 260
6.2.5.4 Is the Emergence of New S Alleles a Gradual Process? 261
6.2.5.5 Nature of the Relationship (Homology or Convergence) Between the S Proteins of the Different Families of Plants That Share a Common SI System 261
6.2.5.6 Evolution of Heteromorphic SI 261
6.2.6 Inter-Species Incompatibility and Incongruity 262
6.2.6.1 The Complexity of PollenPistil Barriers Between Species 262
6.2.6.2 The Need for Further Research on the Molecular Biology of Pre-Zygotic Barriers Between Species 262
6.2.6.3 Selection of Bridging Lines 263
References 265
Subject Index 309
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