Mangroves invade some very marginal habitats for woody plants—at the interface between land and sea. Since mangroves anchor tropical coastal communities globally, their origin, diversification and adaptation are of scientific significance, particularly at a time of global climate change. In this study, a combination of single-molecule long reads and the more conventional short reads are generated from Rhizophora apiculata for the de novo assembly of its genome to a near chromosome level. The longest scaffold, N50 and N90 for the R. apiculata genome, are 13.3 Mb, 5.4 Mb and 1.0 Mb, respectively. Short reads for the genomes and transcriptomes of eight related species are also generated. We find that the ancestor of Rhizophoreae experienced a whole-genome duplication ~70 Myrs ago, which is followed rather quickly by colonization and species diversification. Mangroves exhibit pan-exome modifications of amino acid (AA) usage as well as unusual AA substitutions among closely related species. The usage and substitution of AAs, unique among plants surveyed, is correlated with the rapid evolution of proteins in mangroves. A small subset of these substitutions is associated with mangroves’ highly specialized traits (vivipary and red bark) thought to be adaptive in the intertidal habitats. Despite the many adaptive features, mangroves are among the least genetically diverse plants, likely the result of continual habitat turnovers caused by repeated rises and falls of sea level in the geologically recent past. Mangrove genomes thus inform about their past evolutionary success as well as portend a possibly difficult future.

Polyploidy has been a common process during the evolution of eukaryotes, especially plants, leading to speciation and the evolution of new gene functions. Gene expression levels and patterns can change, and gene silencing can occur in allopolyploids-phenomena sometimes referred to as "transcriptome shock." Alternative splicing (AS) creates multiple mature mRNAs from a single type of precursor mRNA. Here we examined the evolution of AS patterns after polyploidy, with natural and two resynthesized allotetraploid Brassica napus lines, using RT-PCR and sequencing assays of 82 AS events in duplicated gene pairs (homeologs). Comparing the AS patterns between the two homeologs in natural B. napus revealed that many of the gene pairs show different AS patterns, with a few showing variation that was organ specific or induced by abiotic stress treatments. In the resynthesized allotetraploids, 26-30% of the duplicated genes showed changes in AS compared with the parents, including many cases of AS event loss after polyploidy. Parallel losses of many AS events after allopolyploidy were detected in the two independently resynthesized lines. More changes occurred in parallel between the two lines than changes specific to each line. The PASTICCINO gene showed partitioning of two AS events between the two homeologs in the resynthesized allopolyploids. AS changes after allopolyploidy were much more common than homeolog silencing. Our findings indicate that AS patterns can change rapidly after polyploidy, that many genes are affected, and that AS changes are an important component of the transcriptome shock experienced by new allopolyploids.gene duplication | whole genome duplication | molecular evolution P olyploidy is ubiquitous in plants, with many plants being evolutionarily recent polyploids, and all angiosperms having one or more ancient polyploidy events in their lineage (1-3). Polyploids can display novel phenotypes that may contribute to their evolutionary success (4). Gene expression levels and patterns in natural and synthetic polyploids have been widely studied to investigate the immediate and long-term effects of polyploidy. Some of the phenomena revealed include nonadditive patterns of gene expression in polyploids compared with their progenitors, divergence in expression levels and patterns between the homeologs, and gene silencing, with the effects being variable in different organ types, in different developmental stages, and in response to abiotic stresses (reviewed in refs. 5-8).Alternative splicing (AS) is a posttranscriptional mechanism that can regulate gene expression. AS also allows multiple proteins to be produced from the same gene. In addition, AS can cause transcript degradation by including premature stop codons within the coding region that target the transcripts for nonsensemediated decay, and potentially lower levels of gene expression (9, 10). Premature stop codons introduced by AS can sometimes result in truncated proteins that are functional (11). AS can result in phenotypic changes and impact m...

Sonerileae/Dissochaeteae (Melastomataceae) comprises ca. 50 genera, two thirds of which occur in Southeast Asia. Phylogenetic relationships within this clade remain largely unclear, which hampers our understanding of its origin, evolution, and biogeography. Here, we explored the use of chloroplast genomes in phylogenetic reconstruction of Sonerileae/Dissochaeteae, by sampling 138 species and 23 genera in this clade. A total of 151 complete plastid genomes were assembled for this study. Plastid genomic data provided better support for the backbone of the Sonerileae/Dissochaeteae phylogeny, and also for relationships among most closely related species, but failed to resolve the short internodes likely resulted from rapid radiation. Trees inferred from plastid genome and nrITS sequences were largely congruent regarding the major lineages of Sonerileae/Dissochaeteae. The present analyses recovered 15 major lineages well recognized in both nrITS and plastid phylogeny. Molecular dating and biogeographical analyses indicated a South American origin for Sonerileae/Dissochaeteae during late Eocene (stem age: 34.78 Mya). Two dispersal events from South America to the Old World were detected in late Eocene (33.96 Mya) and Mid Oligocene (28.33 Mya) respectively. The core Asian clade began to diversify around early Miocene in Indo-Burma and dispersed subsequently to Malesia and Sino-Japanese regions, possibly promoted by global temperature changes and East Asian monsoon activity. Our analyses supported previous hypothesis that Medinilla reached Madagascar by transoceanic dispersal in Miocene. In addition, generic limits of some genera concerned were discussed.

BackgroundA large-scale systematical investigation of the influence of Pleistocene climate oscillation on mangrove population dynamics could enrich our knowledge about the evolutionary history during times of historical climate change, which in turn may provide important information for their conservation.ResultsIn this study, phylogeography of a mangrove tree Sonneratia alba was studied by sequencing three chloroplast fragments and seven nuclear genes. A low level of genetic diversity at the population level was detected across its range, especially at the range margins, which was mainly attributed to the steep sea-level drop and associated climate fluctuations during the Pleistocene glacial periods. Extremely small effective population size (Ne) was inferred in populations from both eastern and western Malay Peninsula (44 and 396, respectively), mirroring the fragility of mangrove plants and their paucity of robustness against future climate perturbations and human activity. Two major genetic lineages of high divergence were identified in the two mangrove biodiversity centres: the Indo-Malesia and Australasia regions. The estimated splitting time between these two lineages was 3.153 million year ago (MYA), suggesting a role for pre-Pleistocene events in shaping the major diversity patterns of mangrove species. Within the Indo-Malesia region, a subdivision was implicated between the South China Sea (SCS) and the remaining area with a divergence time of 1.874 MYA, corresponding to glacial vicariance when the emerged Sunda Shelf halted genetic exchange between the western and eastern coasts of the Malay Peninsula during Pleistocene sea-level drops. Notably, genetic admixture was observed in populations at the boundary regions, especially in the two populations near the Malacca Strait, indicating secondary contact between divergent lineages during interglacial periods. These interregional genetic exchanges provided ample opportunity for the re-use of standing genetic variation, which could facilitate mangrove establishment and adaptation in new habitats, especially in the context of global climate changes.ConclusionPhylogeogrpahic analysis in this study reveal that Pleistocene sea-level fluctuations had profound influence on population differentiation of the mangrove tree S. alba. Our study highlights the fragility of mangrove plants and offers a guide for the conservation of coastal mangrove communities experiencing ongoing changes in sea-level.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0849-z) contains supplementary material, which is available to authorized users.

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