Natural hybridization plays important roles in plant evolution and speciation. In this study, we sequenced ribosomal internal transcribed spacer (nrITS), four low-copy nuclear genes (Dbr1, SOS4a, SOS4b and PCRF1) and the chloroplast intergenic spacer trnV-trnM to test the hypothesis of hybridization between two species of Phyllagathis and Sporoxeia (Sonerileae/Dissochaeteae, Melastomataceae). Our results provided compelling evidence for the hybridization hypothesis. All hybrid individuals sampled were first-generation hybrids. The failure of flower production in the F1 hybrid individuals may work as the barrier preventing later-generation hybridization or backcross. Analysis of the chloroplast trnV-trnM sequences showed that the hybridization is bidirectional with S. petelotii as the major maternal parent. Several factors, such as sympatry, similar habitat preference, overlapping flowering season and shared pollinators, might have contributed to this hybridization event. The "intergeneric" hybridization reported in this study suggests close relationship between P. longicalcarata and S. petelotii.
Background Mitogenome sizes of seed plants vary substantially even among closely related species, which are often related to horizontal or intracellular DNA transfer (HDT or IDT) events. However, the mechanisms of this size variation have not been well characterized. Results Here we assembled and characterized the mitogenomes of three species of Melastoma, a tropical shrub genus experiencing rapid speciation. The mitogenomes of M. candidum (Mc), M. sanguineum (Ms) and M. dodecandrum (Md) were assembled to a circular mapping chromosome of 391,595 bp, 395,542 bp and 412,026 bp, respectively. While the mitogenomes of Mc and Ms showed good collinearity except for a large inversion of ~ 150 kb, there were many rearrangements in the mitogenomes between Md and either Mc or Ms. Most non-alignable sequences (> 80%) between Mc and Ms are from gain or loss of mitochondrial sequences. Whereas, between Md and either Mc or Ms, non-alignable sequences in Md are mainly chloroplast derived sequences (> 30%) and from putative horizontal DNA transfers (> 30%), and those in both Mc and Ms are from gain or loss of mitochondrial sequences (> 80%). We also identified a recurrent IDT event in another congeneric species, M. penicillatum, which has not been fixed as it is only found in one of the three examined populations. Conclusions By characterizing mitochondrial genome sequences of Melastoma, our study not only helps understand mitogenome size evolution in closely related species, but also cautions different evolutionary histories of mitochondrial regions due to potential recurrent IDT events in some populations or species.
Macrothelypteris torresiana is a reputed medicinal fern. Its complete chloroplast genome was determined by Illumina paired-end sequencing. The genome is 151,150 bp in length with 43.1% overall Guanine+Cytosine (GC) content, which is divided into four distinct parts such as a small single copy (SSC, 21,772 bp), a large single copy (LSC, 82,422 bp), and two inverted repeats (IRs, 23,478 bp each). It contains 132 genes, including 86 protein-coding genes, eight ribosomal RNA genes, 35 tRNA genes, and three pseudogenes. Maximum likelihood (ML) tree revealed that M. torresiana was closely grouped with Christella appendiculata with 100% bootstrap value.
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