Genetic Control Of Self-incompatibility Research Articles

Genetic Mapping of the Incompatibility Locus in Olive and Development of a Linked Sequence-Tagged Site Marker.

The genetic control of self-incompatibility (SI) has been recently disclosed in olive. Inter-varietal crossing confirmed the presence of only two incompatibility groups (G1 and G2), suggesting a simple Mendelian inheritance of the trait. A double digest restriction associated DNA (ddRAD) sequencing of a biparental population segregating for incompatibility groups has been performed and high-density linkage maps were constructed in order to map the SI locus and identify gene candidates and linked markers. The progeny consisted of a full-sib family of 229 individuals derived from the cross ‘Leccino’ (G1) × ‘Dolce Agogia’ (G2) varieties, segregating 1:1 (G1:G2), in accordance with a diallelic self-incompatibility (DSI) model. A total of 16,743 single nucleotide polymorphisms was identified, 7,006 in the female parent ‘Leccino’ and 9,737 in the male parent ‘Dolce Agogia.’ Each parental map consisted of 23 linkage groups and showed an unusual large size (5,680 cM in ‘Leccino’ and 3,538 cM in ‘Dolce Agogia’). Recombination was decreased across all linkage groups in pollen mother cells of ‘Dolce Agogia,’ the parent with higher heterozygosity, compared to megaspore mother cells of ‘Leccino,’ in a context of a species that showed exceptionally high recombination rates. A subset of 109 adult plants was assigned to either incompatibility group by a stigma test and the diallelic self-incompatibility (DSI) locus was mapped to an interval of 5.4 cM on linkage group 18. This region spanned a size of approximately 300 Kb in the olive genome assembly. We developed a sequence-tagged site marker in the DSI locus and identified five haplotypes in 57 cultivars with known incompatibility group assignment. A combination of two single-nucleotide polymorphisms (SNPs) was sufficient to predict G1 or G2 phenotypes in olive cultivars, enabling early marker-assisted selection of compatible genotypes and allowing for a rapid screening of inter-compatibility among cultivars in order to guarantee effective fertilization and increase olive production. The construction of high-density linkage maps has led to the development of the first functional marker in olive and provided positional candidate genes in the SI locus.

Biplot approach with self-incompatibility analyses of sib diallel cross data for Lysimachia monelli (Primulaceae)

The biplot is a diagnostic tool used to make a visual appraisal of large data matrices with double entries. It has been most commonly used in crop breeding to evaluate genotype × environment interactions. We have employed the biplot method to study the self- and cross-compatibility reactions as evinced by diallel crosses for full-sib progeny arrays in Lysimachia (Anagallis) monelli, a species that has been shown to have single locus, multiallelic self-incompatibility, homomorphic gametophytic type (GSI). The resultant plots show two and three major groups (inter-compatible, intra-incompatible). In all diallel biplots, the high proportion of the total variation explained by two principal components (PC1 and PC2) indicates one-locus SI. Two to four compatible/incompatible clusters found in the analyzed diallels is in accord with a GSI type. More interestingly, the biplots also showed varying degrees of interaction between plants as females (pollen receiving) and plants as males (pollen donors) in the data from two diallels. The biplot method offers an alternative approach to study the genetic control of self-incompatibility via diallel crosses, and we propose that it might be particularly useful to study complex self-incompatibility systems in which conventional methods for the analysis of sib diallel results have proven difficult.

The pollen S-determinant in Papaver: comparisons with known plant receptors and protein ligand partners

Cell-cell communication is vital to multicellular organisms and much of it is controlled by the interactions of secreted protein ligands (or other molecules) with cell surface receptors. In plants, receptor-ligand interactions are known to control phenomena as diverse as floral abscission, shoot apical meristem maintenance, wound response, and self-incompatibility (SI). SI, in which 'self' (incompatible) pollen is rejected, is a classic cell-cell recognition system. Genetic control of SI is maintained by an S-locus, in which male (pollen) and female (pistil) S-determinants are encoded. In Papaver rhoeas, PrsS proteins encoded by the pistil S-determinant interact with incompatible pollen to effect inhibition of pollen growth via a Ca(2+)-dependent signalling network, resulting in programmed cell death of 'self' pollen. Recent studies are described here that identified and characterized the pollen S-determinant of SI in P. rhoeas. Cloning of three alleles of a highly polymorphic pollen-expressed gene, PrpS, which is linked to pistil-expressed PrsS revealed that PrpS encodes a novel approximately 20 kDa transmembrane protein. Use of antisense oligodeoxynucleotides provided data showing that PrpS functions in SI and is the pollen S-determinant. Identification of PrpS represents a milestone in the SI field. The nature of PrpS suggests that it belongs to a novel class of 'receptor' proteins. This opens up new questions about plant 'receptor'-ligand pairs, and PrpS-PrsS have been examined in the light of what is known about other receptors and their protein-ligand pairs in plants.

LatentSalleles are widespread in cultivated self-compatibleBrassica napus

The genetic control of self-incompatibility in Brassica napus was investigated using crosses between resynthesized lines of B. napus and cultivars of oilseed rape. These crosses introduced eight C-genome S alleles from Brassica oleracea (S16, S22, S23, S25, S29, S35, S60, and S63) and one A-genome S allele from Brassica rapa (SRM29) into winter oilseed rape. The inheritance of S alleles was monitored using genetic markers and S phenotypes were determined in the F1, F2, first backcross (B1), and testcross (T1) generations. Two different F1 hybrids were used to develop populations of doubled haploid lines that were subjected to genetic mapping and scored for S phenotype. These investigations identified a latent S allele in at least two oilseed rape cultivars and indicated that the S phenotype of these latent alleles was masked by a suppressor system common to oilseed rape. These latent S alleles may be widespread in oilseed rape varieties and are possibly associated with the highly conserved C-genome S locus of these crop types. Segregation for S phenotype in subpopulations uniform for S genotype suggests the existence of suppressor loci that influenced the expression of the S phenotype. These suppressor loci were not linked to the S loci and possessed suppressing alleles in oilseed rape and non-suppressing alleles in the diploid parents of resynthesized B. napus lines.

Genetic control of self-incompatibility in Anagallis monelli (Primulaceae: Myrsinaceae).

The genetic control of self-incompatibility (SI) was studied in the Mediterranean short-lived perennial species Anagallis monelli (Primulaceae: Myrsinaceae). Arrays of siblings, including families derived from reciprocal crosses, were cross-pollinated in full diallels, and compatibility groups were assesssed from a census of fruit-set. Two, three and four intercompatible and intraincompatible groups were found. These crossing relationships fit the model for gametophytic SI controlled by a single polymorphic gene locus in families derived from parents with one or no S alleles in common (two vs. four compatibility groups), whilst one genotype was presumed to be missing in the small families that showed only three compatibility groups.

Auxin modification of the incompatibility response in Theobroma cacao.

The time course and control of floral abscission and fruit set in Theobroma cacao were studied after spray application of growth regulators. 1-Naphthaleneacetic acid (NAA) prevented flower abscission in a concentration dependent manner and induced the early stages of fruit development. The cytokinin benzylaminopurine (BAP) counteracted NAA but resulted in longer fruit retention. Measurements of endogenous levels of indole-3-acetic acid showed an inverse correlation between the number of flowers per plant and auxin content. The results suggest that the genetic control of self-incompatibility in T. cacao may be modulated by the hormonal content of the flower.

Genetic control of self-incompatibility in Senecio squalidus L. (Asteraceae): a successful colonizing species.

Senecio squalidus (Oxford ragwort) is a well-known introduction to the British flora that has proved to be an extremely successful colonist over the last 150 years. Unusually for a colonizing species, S. squalidus is self-incompatible (SI). Being a member of the Asteraceae, SI in S. squalidus is expected to be sporophytic. This paper presents genetic data showing that the SI system of S. squalidus is indeed sporophytic and is controlled by a single multiallelic S locus, alleles of which show the dominance/recessive relationships characteristic of sporophytic SI (SSI). Early indications are that the number of S alleles in populations is low because only four different S alleles were identified in a sample of four plants from two distinct populations; one S allele, S1, a pollen/stigma recessive allele, was present in all four plants. Forced inbreeding, using salt-treatment to overcome SI, was shown to generate 'pseudo-self-compatible' individuals with weakened SI and a loss/reduction in stigmatic S-specific discrimination. Relatively high frequencies of unpredictable compatible crossing 'anomalies' suggest that a 'gametophytic element' may influence the outcome of crosses in certain genetic backgrounds so as to increase levels of compatibility when S alleles are shared. Together, these findings indicate a genetic 'flexibility' in the SSI system of S. squalidus that could be crucial to its success as a colonizer.

The genetic control of self-incompatibility in Linanthus parviflorus (Polemoniaceae)

The genetic control of self-incompatibility (SI) was studied in the spring-flowering annual, Linanthus parviflorus (Polemoniceae). Arrays of full-siblings were cross-pollinated in a full-diallel design and compatibility relationships were assessed by examining for pollen tube growth in styles. Two to four incompatibility types were observed in each sibship, some types were interincompatible, and reciprocal differences in incompatibility between types were found. The results demonstrated close agreement with expected patterns of incompatibility among full-siblings for sporophytic control of SI with linear dominance. Taken together, these results provide support for sporophytic SI in L. parviflorus. The crossing data presented here are contrasted with results of a previous study indicating gametophytic control of SI in Phlox drummondii, another polemoniaceous species.

The genetic control of self-incompatibility in Linanthus parviflorus (Polemoniaceae)

The genetic control of self-incompatibility (SI) was studied in the spring-flowering annual, Linanthus parviflorus (Polemoniceae). Arrays of full-siblings were cross-pollinated in a full-diallel design and compatibility relationships were assessed by examining for pollen tube growth in styles. Two to four incompatibility types were observed in each sibship, some types were interincompatible, and reciprocal differences in incompatibility between types were found. The results demonstrated close agreement with expected patterns of incompatibility among full-siblings for sporophytic control of SI with linear dominance. Taken together, these results provide support for sporophytic SI in L. parviflorus. The crossing data presented here are contrasted with results of a previous study indicating gametophytic control of SI in Phlox drummondii, another polemoniaceous species.

S-gene polymorphism in Phlox drummondii

The genetic control of self-incompatibility and the number of S-alleles were studied in a population of Phlox drummondii from Lytle, Texas. Thirty-four seedlings were transplanted to the greenhouse. Each was self-fertilized (using bud pollination) to generate self families of 9–11 plants. Complete diallels were performed within each family. Twenty-four families contained three cross-compatibility phenotypes whose crossing relationships indicated that self-incompatibility was under gametophytic control and governed by one gene. Homozygotes from twenty-four families were crossed in a half-diallel for S-genotype assignment. Thirty S-alleles were detected. Allele frequencies did not deviate significantly from equality.

Tests of the heterosis model

An alternative to the classical model of self-incompatibility indicates that genetic control of self-incompatibility could involve more than one locus and function through passive failure of incompatible pollen tubes rather than through their active inhibition. Both aspects of the alternative model have been tested and, in each case, the data support the classical single-locus oppositional interpretation rather than the alternative. On the basis of these data, and others now available, we conclude that, in the Solanaceae, and presumably also in some others, self-incompatibility is better explained by the classical interpretation. Several points, however, remain to be resolved.

Genetic control of self-incompatibility in red-osier dogwood

Growth of pollen tubes in the style of redosier dogwood (Cornus sericea) plants was observed after self- and outcross pollinations and seed sets on nine F1 plants crossed in diallel were recorded. Incompatlble pollen tubes were inhibited in the style and the F1 progeny fit into four intraincompatible inter-compatible classes. Self-Incompatibility in C. sericea is controlled by a one-locus, multiallelic gametophytic system.