Aspects Of Self-incompatibility Research Articles

Population genetics of self-incompatibility and developing self-compatible genotypes in niger (Guizotia abyssinica)

Niger (Guizotia abyssinica (L. f.) Cass. (Asteraceae) is a strictly self-incompatible crop species with a sporophytic self-incompatibility mechanism. This characteristic presents a number of difficulties in plant improvement programs. The objective of this study was to determine the number and distribution of S-alleles in Ethiopian niger populations and to identify and develop self-compatible genotypes with various associated advantages. Several aspects of self-incompatibility in niger were compared in self- and cross-pollination experiments in which seed-set was considered to be a measure of compatibility. Our results indicate the presence of a minimum of ten self-incompatibility alleles and one self-compatibility allele at the S-locus in niger. Most of these alleles behave differently in the pollen and pistil. About two-thirds of the allelic interactions in both the pollen and pistil were dominant/recessive, and one-third were codominant. The reciprocal cross-pollinations (RCPs) resulted in progeny with similar levels of compatibility within and among populations because of a wide distribution of S-alleles in the populations and, consequently, low population differentiation at the S-locus. An analysis of molecular variance (AMOVA) revealed that only 2% of the total genetic variation at the S-locus differentiates the populations. In conclusion, self-compatible genotypes from the Ethiopian niger gene pool have been identified and developed for the first time.

Self-incompatibility in flowering plants. Evolution, diversity, and mechanisms

A book about progress in understanding self-incompatibility is a good idea. This topic is a classic, with importance for several different areas within biology, ranging from population and evolutionary genetics to cell biology, and there has been an impressive history of breakthroughs that have, in turn, led to new questions, in a kind of ‘arms race’ where the plants have so far managed to guard the most fascinating secrets. The last time self-incompatibility was reviewed at length and in detail was in de Nettancourt's book, last revised in 2001, and even then it was clear that a single biologist could not review this whole field. This book, sensibly, contains chapters from experts in different aspects of self-incompatibility. Progress in the past 20 years, and the major current puzzles, are therefore well covered, but at a cost of a lack of integration. The editor has provided cross-references, but the disadvantage of a multi-author book is the lack of a clear overview. The final chapter on heteromorphic incompatibility in Primula, for instance, leaves it unclear how (or whether) each system can help us understand the other. The book is therefore most suitable for researchers. Each chapter reviews the authors' area of expertise, and each provides a good account of the current information (often in great detail). Many chapters outline the questions that remain unanswered, but some do not explain the concepts discussed, or sometimes even the evidence for the conclusions stated, and so parts of many chapters will be understandable mainly by people already working on self-incompatibility, or who have already read de Nettancourt's book. These people will read review papers in specialized journals, and, for some topics, the authoritative reviews in the book may quickly be superseded. These problems are perhaps inevitable. Progress in the past 25 years has been enormous – from being able to test different incompatibility types of individual plants, and determine the inheritance and roughly estimate the numbers of different alleles in populations with homomorphic systems, to knowing details of the molecular mechanism of self-incompatibility in different species. This knowledge should lead to new progress, and one value of gathering it into a book is to take stock of current understanding. We still do not know the type of incompatibility inheritance in many taxa, and the genes responsible have been identified only in very few taxa (the sporophytic system of Brassica family members, and the very different gametophytic systems in Papaver rhoeas, and in some Solanaceae, Rosaceae and Antirrhinum). In some RNase-based systems, as clearly reviewed by J. Kohn, the pollen recognition gene remains puzzling, because the best candidates in most species do not seem to have the predicted high sequence diversity (which is found in the Solanaceae, P. rhoeas and the Brassica family members) and different mechanisms could be involved in different RNase-based systems. Genetic studies are still very laborious, even in short-lived plants, and most self-incompatible taxa remain unstudied. This book contains useful chapters on two groups whose incompatibility systems remain unknown at the molecular level, the two-locus gametophytic system in grasses (whose S and Z loci may soon be discovered using comparative mapping and genome sequencing) and sweet potato (where finding the loci seems tantalisingly close), and two chapters review heterostyled systems. The heterostyly genes seem likely to be discovered before long, now that closely linked regions have been identified. In heterostyly it is, however, possible that a physically large genome non-recombining region, similar to a sex chromosome, is involved, and testing this evolutionary hypothesis is one of the main reasons for studying these systems. A major evolutionary puzzle is how new specificities arise in homomorphic multi-allele systems with linked pistil and pollen genes. This remains as mysterious as ever, as J. Kohn's chapter explains. It should be helpful to be able to identify alleles with different incompatibility types in natural samples, and it is now clear that alleles with different incompatibility types differ greatly in sequence (such polymorphism is now a criterion used along with functional tests to show that a candidate is indeed an incompatibility gene). If alleles of the same incompatibility type are generally very similar (as has also been shown), then sequences can be used to identify alleles. A book with a range as broad as this should show how the achievements so far can help answer the unresolved questions; however, by the end, it is hard to have a clear feeling for what questions should be asked next to further understanding of self-incompatibility.

Structural and molecular analysis of self-incompatibility in almond ( Prunus dulcis )

A multi-approach was used to study different aspects of self-incompatibility (SI) in almond (Prunus dulcis). First, a population of almond cultivars was characterised as to their individual S-allele combination using separation of stylar protein extracts (non-equilibrium pH gradient electrofocusing) followed by staining for RNase activity, which led to the identification of one putative new allele and several new S-allele combinations. Second, a field pollination scheme was designed to study pollen tube progression and to obtain a spatial and temporal characterisation of this reproductive stage in both incompatible and compatible crosses. In addition, an anti-serum was raised against a synthetic peptide designed from an almond S-protein (S8) and used for immunological in situ detection in pistil cryosections. S-RNases were found to accumulate intercellularly in the stylar transmitting tissue as previously reported for other rosaceous species. The results are discussed in view of the evolution of the gametophytic SI system and the models proposed for its mechanism. Gametophyte selection is also proposed as an important intraspecific barrier to fertilisation in this species.

Construction of a binary bacterial artificial chromosome library ofPetunia inflataand the isolation of large genomic fragments linked to the self-incompatibility (S-) locus

The Solanaceae family of flowering plants possesses a type of self-incompatibility mechanism that enables the pistil to reject self pollen but accept non-self pollen for fertilization. The pistil function in this system has been shown to be controlled by a polymorphic gene at the S-locus, termed the S-RNase gene. The pollen function is believed to be controlled by another as yet unidentified polymorphic gene at the S-locus, termed the pollen S-gene. As a first step in using a functional genomic approach to identify the pollen S-gene, a genomic BAC (bacterial artificial chromosome) library of the S2S2genotype of Petunia inflata, a self-incompatible solanaceous species, was constructed using a Ti-plasmid based BAC vector, BIBAC2. The average insert size was 136.4 kb and the entire library represented a 7.5-fold genome coverage. Screening of the library using cDNAs for the S2-RNase gene and 13 pollen-expressed genes that are linked to the S-locus yielded 51 positive clones, with at least one positive clone for each gene. Collectively, at least 2 Mb of the chromosomal region was spanned by these clones. Together, three clones that contained the S2-RNase gene spanned ~263 kb. How this BAC library and the clones identified could be used to identify the pollen S-gene and to study other aspects of self-incompatibility is discussed.Key words: bacterial artificial chromosome, Petunia inflata, pollen-pistil interactions, self-incompatibility, S-locus.

Construction of a binary bacterial artificial chromosome library of <i>Petunia inflata</i> and the isolation of large genomic fragments linked to the self-incompatibility (<i>S-</i>) locus

The Solanaceae family of flowering plants possesses a type of self-incompatibility mechanism that enables the pistil to reject self pollen but accept non-self pollen for fertilization. The pistil function in this system has been shown to be controlled by a polymorphic gene at the S-locus, termed the S-RNase gene. The pollen function is believed to be controlled by another as yet unidentified polymorphic gene at the S-locus, termed the pollen S-gene. As a first step in using a functional genomic approach to identify the pollen S-gene, a genomic BAC (bacterial artificial chromosome) library of the S2S2 genotype of Petunia inflata, a self-incompatible solanaceous species, was constructed using a Ti-plasmid based BAC vector, BIBAC2. The average insert size was 136.4 kb and the entire library represented a 7.5-fold genome coverage. Screening of the library using cDNAs for the S2-RNase gene and 13 pollen-expressed genes that are linked to the S-locus yielded 51 positive clones, with at least one positive clone for each gene. Collectively, at least 2 Mb of the chromosomal region was spanned by these clones. Together, three clones that contained the S2-RNase gene spanned approximately 263 kb. How this BAC library and the clones identified could be used to identify the pollen S-gene and to study other aspects of self-incompatibility is discussed.

Molecular Aspects of Self-Incompatibility in Flowering Plants

Molecular Aspects of Self-Incompatibility in Flowering Plants

Recent developments in the molecular genetics and biology of self-incompatibility

A summary of recent work on molecular aspects of self-incompatibility in Nicotiana alata is presented. The amino acid sequences of style proteins corresponding to different S-alleles of N. alata have a high level of homology in some regions and are variable in other regions. The regions of homology include N-terminal sequences as well as most of the glycosylation sites and cysteine residues. The glycosyl substituents may consist of a number of 'glycoforms'. The isolated style S-glycoproteins inhibit in vitro growth of pollen tubes. The S-glycoproteins tested inhibited the growth of pollen of several S-genotypes, and there was some specificity in the interaction. Heat treatment of the isolated S-glycoproteins dramatically increased their activity as inhibitors of pollen tube growth, although the specificity in the interaction was lost. The nature of the S-allele products in pollen is not yet established.