Efficient molecular sexing in dioecious Silene latifolia and S. dioica and paternity analysis in F(1) hybrids

Two novel PCR-based assays for sexing of Silene latifolia and Silene dioica plants

Silene latifolia and S. dioica are model systems in studies of plant reproduction, chromosome evolution and sexual dimorphism, but sexing of plants based on morphology is only possible from flowering stage onwards. Both species show homogametic females (XX) and heterogametic males (XY).•Here we developed two assays (primer pairs ss816 and ss441) for molecular sexing of S. latifolia and S. dioica, targeting length polymorphisms between the X and Y-linked copies of the spermidine synthase gene.The two assays were successful in identifying known (flowering-stage) males and females from UK and Spanish populations, with an error rate of 3.1% (ss816; successful for both species) and 0% (ss441, only successful for S. latifolia). Our assays therefore represent novel tools for rapid, robust and simple determination of the genotypic sex of S. latifolia and S. dioica.

Seed shape and size of Silene latifolia, differences between sexes, and influence of the parental genome in hybrids with Silene dioica

Introduction

Plants undergo various natural changes that dramatically modify their genomes. One is polyploidization and the second is hybridization. Both are regarded as key factors in plant evolution and result in phenotypic differences in different plant organs. In Silene, we can find both examples in nature, and this genus has a seed shape diversity that has long been recognized as a valuable source of information for infrageneric classification.

Methods

Morphometric analysis is a statistical study of shape and size and their covariations with other variables. Traditionally, seed shape description was limited to an approximate comparison with geometric figures (rounded, globular, reniform, or heart-shaped). Seed shape quantification has been based on direct measurements, such as area, perimeter, length, and width, narrowing statistical analysis. We used seed images and processed them to obtain silhouettes. We performed geometric morphometric analyses, such as similarity to geometric models and elliptic Fourier analysis, to study the hybrid offspring of S. latifolia and S. dioica.

Results

We generated synthetic tetraploids of Silene latifolia and performed controlled crosses between diploid S. latifolia and Silene dioica to analyze seed morphology. After imaging capture and post-processing, statistical analysis revealed differences in seed size, but not in shape, between S. latifolia diploids and tetraploids, as well as some differences in shape among the parentals and hybrids. A detailed inspection using fluorescence microscopy allowed for the identification of shape differences in the cells of the seed coat. In the case of hybrids, differences were found in circularity and solidity. Overal seed shape is maternally regulated for both species, whereas cell shape cannot be associated with any of the sexes.

Discussion

Our results provide additional tools useful for the combination of morphology with genetics, ecology or taxonomy. Seed shape is a robust indicator that can be used as a complementary tool for the genetic and phylogenetic analyses of Silene hybrid populations.

The X chromosome is necessary for ovule production in Silene latifolia

Sex chromosomes stop recombining and accumulate differences over time. In particular, genes on the chromosome restricted to the heterogametic sex degenerate and become non-functional. Here, we investigated whether or not the degeneration of a plant Y chromosome was sufficient to cause ovules containing a Y to fail to develop, thereby eliminating the possibility of YY individuals. We used two genotypic assays to determine the genotype-XX, XY, or YY-of offspring from a single fruit of an otherwise normal male XY plant of Silene latifolia. The fruit contained fewer ovules than normal pistillate flowers, produced an equal offspring sex ratio, and generated no YY offspring. The results indicate that ovaries must contain an X chromosome to develop properly. While haploid selection has slowed down Y-chromosome degeneration in S. latifolia, we find that it has progressed sufficiently to prevent the proper development of ovules, and hence prevent the presence of YY individuals.

De novo transcriptome assembly of loggerhead sea turtle nesting of the Colombian Caribbean

Loggerhead sea turtle Caretta caretta is widely distributed in the oceans of tropical and subtropical latitude. This turtle is an endangered species due to anthropic and natural factors that have decreased their population levels. In this study, RNA sequencing and de-novo assembly of genes expressed in blood were performed. The raw FASTQ files have been deposited on NCBI's SRA database with accession number SRX2629512. A total of 5.4 Gb raw sequence data were obtained, corresponding to 48,257,019 raw reads. Trinity pipeline was used to perform a de-novo assembly, we were able to identify 64,930 transcripts for female loggerhead turtle transcriptome with an N50 of 1131 bp. The obtained transcriptome data will be useful for further studies of the physiology, biochemistry and evolution in this species.

De novo transcriptome assembly of heavy metal tolerant Silene dioica

Silene dioica is a dioecious plant of the family Caryophyllaceae. In the present study, we used Illumina sequencing technology (MiSeq) to sequence, de novo assembly and annotate the transcriptomes of male and female copper tolerant S. dioica individuals. We sequenced the normalized mRNA of roots, shoots, flower buds and flowers for each sex. Raw reads of the transcriptome assembly project for S. dioica male and female individual have been deposited in NCBI's Sequence Read Archive (SRA) database with the accession number SRP094611. The Trinity and Detonate program was used to de novo assembly 92,347 transcripts for male and 94,757 transcripts for female transcriptome. The assembled transcriptome sequences for S. dioica male and female individuals can be accessed at NCBI with the following accession numbers: GFCG00000000 (male); GFCH00000000 (female). The obtained transcriptomic data will be useful for further studies focusing on copper tolerance, comparative transcriptome analysis with other Silene species and sex chromosomes evolution.

Differential adaptation drives ecological speciation in campions (Silene): evidence from a multi-site transplant experiment

In order to investigate the role of differential adaptation for the evolution of reproductive barriers, we conducted a multi-site transplant experiment with the dioecious sister species Silene dioica and S. latifolia and their hybrids. Crosses within species as well as reciprocal first-generation (F₁ ) and second-generation (F₂ ) interspecific hybrids were transplanted into six sites, three within each species' habitat. Survival and flowering were recorded over 4 yr. At all transplant sites, the local species outperformed the foreign species, reciprocal F₁ hybrids performed intermediately and F₂ hybrids underperformed in comparison to F₁ hybrids (hybrid breakdown). Females generally had slightly higher cumulative fitness than males in both within- and between-species crosses and we thus found little evidence for Haldane's rule acting on field performance. The strength of selection against F₁ and F₂ hybrids as well as hybrid breakdown increased with increasing strength of habitat adaptation (i.e. the relative fitness difference between the local and the foreign species) across sites. Our results suggest that differential habitat adaptation led to ecologically dependent post-zygotic reproductive barriers and drives divergence and speciation in this Silene system.

The X chromosome is necessary for somatic development in the dioecious Silene latifolia: cytogenetic and molecular evidence and sequencing of a haploid genome

Silene latifolia (or white campion) possesses a well-established sex determination system with a dominant Y chromosome in males (the mammalian type). The heteromorphic sex chromosomes X and Y in S. latifolia largely stopped recombination; thus, we can expect a gradual genetic degeneration of the Y chromosome. It is well proven that neither diploid nor polyploid S. latifolia sporophytes can survive without at least one X, so the only life stage possessing the Y as the sole sex chromosome is the male gametophyte (pollen tube), while the female gametophyte seems to be X-dependent. Previous studies on anther-derived plants of this species showed that the obtained plants (largely haploid or dihaploid) were phenotypically and cytologically female. In this paper, we provide molecular evidence for the inviability of plants lacking the X chromosome. Using sex-specific PCR primers, we show that all plantlets and plants derived from anther cultures are female. In studying anther-derived diploid females by sequencing of X-linked markers, we demonstrate that these plants are really homozygous dihaploids. A haploid regenerant plant was sequenced (8× genome coverage) using Illumina technology. Genome data are disposable in the EMBL database as a standard for full genome and X chromosome assembly in this model species. Homozygous dihaploids were back-crossed with males to yield a progeny useful for the study of the evolution of the Y chromosome.