Nonself-recognition-based self-incompatibility can alternatively promote or prevent introgression

1SummaryTraditionally, we expect that self-incompatibility alleles (S-alleles), which prevent self-fertilization, should benefit from negative-frequency dependent selection and rise to high frequency when introduced to a new population through gene flow. However, the most taxonomically widespread form of self-incompatibility, the ribonuclease-based system ancestral to the core eudicots, functions through nonself-recognition, which drastically alters the process of S-allele diversification.We analyze a model of S-allele evolution in two populations connected by migration, focusing on comparisons among the fates of S-alleles originally unique to each population and those shared among populations.We find that both shared and unique S-alleles originating from the population with more unique S-alleles were usually fitter than S-alleles from the population with fewer. Resident S-alleles were often driven extinct and replaced by migrant S-alleles, though this outcome could be averted by pollen limitation or biased migration.Nonself-recognition-based self-incompatibility will usually either disfavor introgression of S-alleles or result in the whole-sale replacement of S-alleles from one population with those from another.

Assessment of Mating System in Helianthus annuus and H. petiolaris (Asteraceae) Populations

Helianthus annuus subsp. annuus and H. petiolaris are wild North American species that have been naturalized in central Argentina. They have a sporophytic self-incompatibility genetic system that prevent self-fertilization but the occurrence of self-compatible plants in Argentina was observed in both species and could in part explain their highly invasive ability. Their geographical distribution coincides with the major crop area. The domestic sunflower is self-compatible, can hybridize with both species and presents a considerable amount of gene flow. The aim of this study is to understand the self-incompatibility mechanism in both wild Helianthus species. Reciprocal crossing and seed production were used to identify self-compatible genotypes, the number and distribution of self-incompatibility alleles within populations and the type and extent of allelic interactions in the pollen and pistil. The behaviour of S alleles within each population was explained by five functional S alleles and one non-functional allele in each species, differing in their presence and frequency within accessions. In both species, the allelic interactions were of dominance/recessiveness and codominance in pollen, whereas it was only codominance in the pistil. Inbreeding effects in wild materials appeared in the third generation of self-pollination, with lethal effects in most plants. The number of S alleles is low and they behave in a similar way of other Asteraceae species. The self-compatibility was addressed to non-functional S alleles introgressed in wild Helianthus plants through gene flow from self-compatible sunflower.

Base-Pairing Requirements for Small RNA-Mediated Gene Silencing of Recessive Self-Incompatibility Alleles in Arabidopsis halleri

Small noncoding RNAs are central regulators of genome activity and stability. Their regulatory function typically involves sequence similarity with their target sites, but understanding the criteria by which they specifically recognize and regulate their targets across the genome remains a major challenge in the field, especially in the face of the diversity of silencing pathways involved. The dominance hierarchy among self-incompatibility alleles in Brassicaceae is controlled by interactions between a highly diversified set of small noncoding RNAs produced by dominant S-alleles and their corresponding target sites on recessive S-alleles. By controlled crosses, we created numerous heterozygous combinations of S-alleles in Arabidopsis halleri and developed an real-time quantitative PCR assay to compare allele-specific transcript levels for the pollen determinant of self-incompatibility (SCR). This provides the unique opportunity to evaluate the precise base-pairing requirements for effective transcriptional regulation of this target gene. We found strong transcriptional silencing of recessive SCR alleles in all heterozygote combinations examined. A simple threshold model of base pairing for the small RNA–target interaction captures most of the variation in SCR transcript levels. For a subset of S-alleles, we also measured allele-specific transcript levels of the determinant of pistil specificity (SRK), and found sharply distinct expression dynamics throughout flower development between SCR and SRK. In contrast to SCR, both SRK alleles were expressed at similar levels in the heterozygote genotypes examined, suggesting no transcriptional control of dominance for this gene. We discuss the implications for the evolutionary processes associated with the origin and maintenance of the dominance hierarchy among self-incompatibility alleles.

Detecting and determining self-incompatibility alleles in almond genotypes using molecular method.

One of the problems in almond production is self-incompatibility in this plant, which is considered as an important improvement point for this tree. Self-incompatibility causes non-uniformity and garden management problems. Most cultivars of almonds have gametophytic self-incompatibility that is controlled by a multi-allelic gene site. The inoculation inhibitor factor in this inhibitory system is the stop of pollen tube growth in the style. This study aims to detect and determine the self-compatible genotype from among the studied samples and determine the self-incompatibility alleles in the studied masses. For the experiment, the leaf samples were collected from 100 almond genotypes that had good products in recent years. The DNA of young leaf samples in these genotypes was extracted using Gept and Celeg (1989) method with a few changes. Today, various methods have been invented for detecting the genotypes and self-compatible cultivars from selfincompatible cultivars as well as S alleles in almonds, including the PCR method. Therefore, in order to detect S alleles in different almond and some hybrid genotypes, the exclusive primer pairs, including AS1II-AmyC5R, ConF-ConR and Cebador2-Cebador8, were used in the polymerase chain reaction. All of the primers have been used by other researchers to detect almond alleles and the effectiveness of these pairs of primers was confirmed in this experiment. Using the AS1IIAmyC5R and Cebador2-Cebador8 primers, the Sf allele with the size of 1200 base pairs was detected. Using the ConF-ConR pair of primer, the S1, S2, S3, S10, S11, S23, and S31 alleles were detected in the self-incompatible samples. Using AS1II-AmyC5R pair of primer, the known alleles of S3, Sf, S2, S1, S5, S10, S11, S23, and S13 were detected. The other bands obtained from the PCR were related to the known self-incompatibility alleles that might be considered as new alleles. In the study population in this research, S1, S2, S3, and S11 alleles had higher frequency.

Self-Incompatibility Alleles in Iranian Pear Cultivars

In the present study, the S-alleles of eighteen pear cultivars, (including fourteen cultivars planted commercially in Iran and four controls) are determined. 34 out of 36 S-alleles are detected using nine allele-specific primers, which are designed for amplification of S101/S102, S105, S106, S107, S108, S109, S111, S112 and S114, as well as consensus primers, PycomC1F and PycomC5R. S104, S101 and S105 were the most common S-alleles observed, respectively, in eight, seven and six cultivars. In 16 cultivars, (‘Bartlett’ (S101S102), ‘Beurre Giffard’ (S101S106), ‘Comice’ (S104S105), ‘Doshes’ (S104S107), ‘Koshia’ (S104S108), ‘Paskolmar’ (S101S105), ‘Felestini’ (S101S107), ‘Domkaj’ (S104S120), ‘Ghousi’ (S104S107), ‘Kaftar Bache’ (S104S120), ‘Konjoni’ (S104S108), ‘Laleh’ (S105S108), ‘Natanzi’ (S104S105), ‘Sebri’ (S101S104), ‘Se Fasleh’ (S101S105) and ‘Louise Bonne’ (S101S108)) both alleles are identified but in two cultivars, (‘Pighambari’ (S105) and ‘Shah Miveh Esfahan’ (S107)) only one allele is recognized. It is concluded that allele-specific PCR amplification can be considered as an efficient and rapid method to identify S-genotype of Iranian pear cultivars.