Polyploid formation is a major mode of sympatric speciation in flowering plants. Unlike other speciation processes, polyploidization is often assumed to confer instant reproductive isolation. Shared polymorphism across ploidy levels has therefore often been attributed to multiple polyploid origins, whereas the alternative hypothesis of introgressive hybridization has rarely been rigorously tested. Here, we sequence 12 nuclear loci representing 6 genes duplicated by polyploidy in 92 accessions of the tetraploid Capsella bursa-pastoris together with the corresponding loci in 21 accessions of its close diploid relative Capsella rubella. In C. bursa-pastoris accessions from western Eurasia, where the 2 species occur in partial sympatry, we find higher levels of nucleotide diversity than in accessions from eastern Eurasia, where C. rubella does not grow. Furthermore, haplotypes are shared across ploidy levels at 4 loci in western but not in eastern Eurasia. We test whether haplotype sharing is due to retention of ancestral polymorphism or due to hybridization and introgression using a coalescent-based isolation-with-migration model. In western but not in eastern Eurasia, there is evidence for unidirectional gene flow from C. rubella to C. bursa-pastoris. An independent estimate of the timing of dispersal of C. bursa-pastoris to eastern Eurasia indicates that it probably predated introgression. Our results show that polyploid speciation need not result in immediate and complete reproductive isolation, that postpolyploidization hybridization and introgression can contribute significantly to genetic variation in a newly formed polyploid, and that divergence population genetic analysis constitutes a powerful way of testing hypotheses on polyploid speciation.

The long-term fates of duplicate genes are well studied both empirically and theoretically, but how the short-term evolution of duplicate genes contributes to phenotypic variation is less well known. Here, we have studied the genetic basis of flowering time variation in the disomic tetraploid Capsella bursa-pastoris. We sequenced four duplicate candidate genes for flowering time and 10 background loci in samples from western Eurasia and China. Using a mixed-model approach that accounts for population structure, we found that polymorphisms at one homeolog of two candidate genes, FLOWERING LOCUS C (FLC) and CRYPTOCHROME1 (CRY1), were associated with natural flowering time variation. No potentially causative polymorphisms were found in the coding region of CRY1; however, at FLC two splice site polymorphisms were associated with early flowering. Accessions harboring nonconsensus splice sites expressed an alternatively spliced transcript or did not express this FLC homeolog. Our results are consistent with the function of FLC as a major repressor of flowering in Arabidopsis thaliana and imply that nonfunctionalization of duplicate genes could provide an important source of phenotypic variation.

The lack of a genomewide effect of allopolyploidy on TE abundance, combined with the increases TE abundance in gene-rich regions, suggests that relaxed selection rather than hybrid breakdown of host silencing explains the TE accumulation in C. bursa-pastoris.

Patchouli plant (Pogostemon cablin (Blanco) Benth.) is of important economic value, and it has been grown for medicinal use for more than 1000 years in China and Southeast Asia. There are limited data to underpin the genetic and genomic resource management for Patchouli. Herein, we used specific-locus amplified fragment sequencing to generate a genetic delineation of P. cablin collected from Vietnam, South China, and Indonesia (Sumatra). In total, 15 457 835 reads, 61 334 specific-locus amplified fragments, and 511 reliable single nucleotide polymorphisms were obtained. On the basis of model-based grouping and neighbor-joining trees, we divided the studied accessions into six distinct groups: one Vietnamese group, two Chinese groups, and three Indonesian groups. We also measured the contents of patchouli alcohol and pogostone; all accessions belonged to patchouloltype except for three accessions from the species' northernmost distribution in China, which have a high content of pogostone. The results from both genetic structure and chemotypes were highly consistent with the possible migration history of Patchouli. Accordingly, ex situ conservation should be immediately established for Patchouli, particularly for the pogostone-type and the germplasm in Vietnam.

Summary• Flowering is a major developmental transition and its timing in relation to environmental conditions is of crucial importance to plant fitness. Understanding the genetic basis of flowering time variation is important to determining how plants adapt locally.• Here, we investigated flowering time variation of Capsella bursa-pastoris collected from different latitudes in China. We also used a digital gene expression (DGE) system to generate partial gene expression profiles for 12 selected samples.• We found that flowering time was highly variable and most strongly correlated with day length and winter temperature. Significant differences in gene expression between early-and late-flowering samples were detected for 72 candidate genes for flowering time. Genes related to circadian rhythms were significantly overrepresented among the differentially expressed genes.• Our data suggest that circadian rhythms and circadian clock genes play an important role in the evolution of flowering time, and C. bursa-pastoris plants exhibit expression differences for candidate genes likely to affect flowering time across the broad range of environments they face in China.

Background and aims The colonization success of a species depends on the interplay between its phenotypic plasticity, adaptive potential and demographic history. Assessing their relative contributions during the different phases of a species range expansion is challenging, and requires large-scale experiments. Here, we investigated the relative contributions of plasticity, performance and demographic history to the worldwide expansion of the shepherd’s purse, Capsella bursa-pastoris. Methods We installed two large common gardens of the shepherd’s purse, a young, self-fertilizing, allopolyploid weed with a worldwide distribution. One common garden was located in Europe, the other in Asia. We used accessions from three distinct genetic clusters (Middle East, Europe, and Asia) that reflect the demographic history of the species. Several life-history traits were measured. To explain the phenotypic variation between and within genetic clusters, we analysed the effects of (i) the genetic clusters, (ii) the phenotypic plasticity and its association to fitness, and (iii) the distance in terms of bioclimatic variables between the sampling site of an accession and the common garden, i.e., the environmental distance. Key results Our experiment showed that (i) the performance of C. bursa-pastoris is closely related to its high phenotypic plasticity; (ii) within a common garden, genetic cluster was a main determinant of phenotypic differences; and (iii) at the scale of the experiment, the effect of environmental distance to the common garden could not be distinguished from that of genetic clusters. Conclusion Phenotypic plasticity and demographic history both play important role at different stages of range expansion. The success of the worldwide expansion of C. bursa-pastoris was undoubtedly influenced by its strong phenotypic plasticity.

Pogostemon cablin (Blanco) Benth. (Patchouli) is not only an important essential oil plant, but also a valuable medicinal plant in China. P . cablin in China can be divided into three cultivars (Shipai, Gaoyao, and Hainan) and two chemotypes (pogostone-type and patchoulol-type). The pogostone-type and patchoulol-type are, respectively, used for medicinals and perfumes. In this study, we sequenced and characterized the plastid genomes for all three Chinese cultivars and aimed to develop a chemotype-specific barcode for future quality control. The plastid genomes of P . cablin cultivars ranged from 152,461 to 152,462 bp in length and comprise 114 genes including 80 protein coding genes, 30 tRNA genes, and four rRNA genes. Phylogenetic analyses suggested that P . cablin cultivars clustered with the other two Pogostemon species with strong support. Although extremely conserved in P . cablin plastid genomes, 58 cpSSRs were filtered out among the three cultivars. One single variable locus, cpSSR, was discovered. The cpSSR genotypes successfully matched the chemotypes of Chinese patchouli, which was further supported by PCR-based Sanger sequences in more Chinese patchouli samples. The barcode developed in this study is thought to be a simple and reliable quality control method for Chinese P . cablin on the market.

Rhizophora stylosa is a true mangrove distributed in the Indo-Pacific region. In this study, the whole chloroplast genome of R. stylosa was assembled and annotated. The chloroplast genome was 164,475 bp in length, consisting of a large single copy (LSC) region of 92,582 bp, a small single copy (SSC) region of 19,243 bp, and two inverted repeat (IR) regions of 26,325 bp. It contained 131 genes, including 85 protein-coding genes, 38 tRNA genes, and eight rRNA genes. The overall GC content was 34.9%. Phylogenetic analysis showed that R. stylosa was sister to Erythroxylum novogranatense.