Reassessment of Annamocarya sinesis (Carya sinensis) Taxonomy through Concatenation and Coalescence Phylogenetic Analysis

Due to its peculiar morphological characteristics, there is dispute as to whether the genus of Annamocarya sinensis, a species of Juglandaceae, is Annamocarya or Carya. Most morphologists believe it should be distinguished from the Carya genus while genomicists suggest that A. sinensis belongs to the Carya genus. To explore the taxonomic status of A. sinensis using chloroplast genes, we collected chloroplast genomes of 16 plant species and assembled chloroplast genomes of 10 unpublished Carya species. We analyzed all 26 species’ chloroplast genomes through two analytical approaches (concatenation and coalescence), using the entire and unique chloroplast coding sequence (CDS) and entire and protein sequences. Our results indicate that the analysis of the CDS and protein sequences or unique CDS and unique protein sequence of chloroplast genomes shows that A. sinensis indeed belongs to the Carya genus. In addition, our analysis shows that, compared to single chloroplast genes, the phylogeny trees constructed using numerous genes showed higher consistency. Moreover, the phylogenetic analysis calculated with the coalescence method and unique gene sequences was more robust than that done with the concatenation method, particularly for analyzing phylogenetically controversial species. Through the analysis, our results concluded that A. sinensis should be called C. sinensis.

Context-Dependent Mutation Dynamics, Not Selection, Explains the Codon Usage Bias of Most Angiosperm Chloroplast Genes

Two competing proposals about the degree to which selection affects codon usage of angiosperm chloroplast genes are examined. The first, based on observations that codon usage does not match expectations under the naïve assumption that base composition will be identical at all neutral sites, is that selection plays a significant role. The second is that codon usage is determined almost solely by mutation bias and drift, with selection influencing only one or two highly expressed genes, in particular psbA. First it is shown that, as a result of an influence of neighboring base composition on mutation dynamics, compositional biases are expected to be widely divergent at different sites in the absence of selection. The observed mutation properties are then used to predict expected neutral codon usage biases and to show that observed deviations from the naïve expectations are in fact expected given the context-dependent mutational dynamics. It is also shown that there is a match between the observed and expected codon usage when context effects are taken into consideration, with psbA being a notable exception. Overall, the data support the model that selection is not a widespread factor affecting the codon usage of angiosperm chloroplast genes and highlight the need to have an accurate model of mutational dynamics.

A Novel Chloroplast Protein RNA Processing 8 Is Required for the Expression of Chloroplast Genes and Chloroplast Development in Arabidopsis thaliana

Chloroplast development involves the coordinated expression of both plastids- and nuclear-encoded genes in higher plants. However, the underlying mechanism still remains largely unknown. In this study, we isolated and characterized an Arabidopsis mutant with an albino lethality phenotype named RNA processing 8 (rp8). Genetic complementation analysis demonstrated that the gene AT4G37920 (RP8) was responsible for the mutated phenotype. The RP8 gene was strongly expressed in photosynthetic tissues at both transcription and translation protein levels. The RP8 protein is localized in the chloroplast and associated with the thylakoid. Disruption of the RP8 gene led to a defect in the accumulation of the rpoA mature transcript, which reduced the level of the RpoA protein, and affected the transcription of PEP-dependent genes. The abundance of the chloroplast rRNA, including 23S, 16S, 4.5S, and 5S rRNA, were reduced in the rp8 mutant, respectively, and the amounts of chloroplast ribosome proteins, such as, PRPS1(uS1c), PRPS5(uS5c), PRPL2 (uL2c), and PRPL4 (uL4c), were substantially decreased in the rp8 mutant, which indicated that knockout of RP8 seriously affected chloroplast translational machinery. Accordingly, the accumulation of photosynthetic proteins was seriously reduced. Taken together, these results indicate that the RP8 protein plays an important regulatory role in the rpoA transcript processing, which is required for the expression of chloroplast genes and chloroplast development in Arabidopsis.

Six Newly Sequenced Chloroplast Genomes From Trentepohliales: The Inflated Genomes, Alternative Genetic Code and Dynamic Evolution

Cephaleuros is often known as an algal pathogen with 19 taxonomically valid species, some of which are responsible for red rust and algal spot diseases in vascular plants. No chloroplast genomes have yet been reported in this genus, and the limited genetic information is an obstacle to understanding the evolution of this genus. In this study, we sequenced six new Trentepohliales chloroplast genomes, including four Cephaleuros and two Trentepohlia. The chloroplast genomes of Trentepohliales are large compared to most green algae, ranging from 216 to 408 kbp. They encode between 93 and 98 genes and have a GC content of 26–36%. All new chloroplast genomes were circular-mapping and lacked a quadripartite structure, in contrast to the previously sequenced Trentepohlia odorata, which does have an inverted repeat. The duplicated trnD-GTC, petD, and atpA genes in C. karstenii may be remnants of the IR region and shed light on its reduction. Chloroplast genes of Trentepohliales show elevated rates of evolution, strong rearrangement dynamics and several genes display an alternative genetic code with reassignment of the UGA/UAG codon presumably coding for arginine. Our results present the first whole chloroplast genome of the genus Cephaleuros and enrich the chloroplast genome resources of Trentepohliales.

Phylogeny of Pyrus and their relationships inferred from sequences of nuclear NIA-i3 intron and chloroplast ndhC-trnV and trnR-atpA

Background: Pear (Pyrus L.) belongs to subtribe Malinae, tribe Maleae, family Rosaceae. According to the geography distribution, it could be divided into Oriental pear and Occidental pear. Though the phylogeny of Pyrus was complicate, previous study referring to morphology, nuclear genes and chloroplast genes made the relationships clear gradually. However, they had lower sequence divergence and less information, therefore it hardly solved the phylogeny of Pyrus. Results: A total of 100 accessions from Oriental and Occidental pears were used to elucidate the phylogeny of Pyrus by one nuclear NIA-i3 intron and two chloroplast regions (ndhC-trnV and trnR-atpA) with higher polymorphism. The Neighbor-Net phylogenetic network indicated that the phylogenetic relationships were complicate based on ndhC-trnV and trnR-atpA. Oriental pear and Occidental pear were separated in the tree of NIA-i3, P. betulaforlia, P. pashia (except P. pashia ‘P10-3’_1 and P. pashia ‘P23-4’_1) were monophyly; several P. ussuriensis were closely related with P. xerophila. However, the phylogenetic relationships of Chinese White Pear, P. pyrifolia and some P. ussuriensis still could not be well solved; West Asian species and European species were mingled together. Occidental pear P. caucasica 684，P. pyraster 989，P. elaeagrifolia 2817 might be hybrids between Oriental pear and Occidental pear.Conclusions: The phylogenetic relationships of Pyrus were still complicate because interspecies and intraspecies of Oriental pear and Occidental pear respectively were intercrossed. More genes and more accessions were needed to solve the phylogenetic relationships in Pyrus and to explore the possible parents.

Amplification rate of matK and rbcL genes in three types of durian

Durian is a tropic fruit having numerous variations on its fruits. Its variations are not only in its shape but also in its aril fruit, aril color, flavor, and aril thickness. In addition to its fruit variations, the genus Durio also has many species which quite hard to distinguish morphologically, except during flowering and fruiting times. This study aimed to determine the genetic relationship among Durian, Pelangi Atuturi Variety Durian, Durio graveolent, and Durio zibetinus based on chloroplast genes (RbcL and matK genes). The primers were previously designed for amplifying matK and rbcL genes based on the Durio zibethinus sequence. Both genes were used because of having great competence to describe genetic relationships between plant species. The rbcL primer could amplify all evaluated samples. Meanwhile, matK primer generated a smeared band in Durian Pelangi; thus, we did not obtain any sequence of this plant. Sequence analysis showed no variation of rbcL sequence in these evaluated species. A similar result was also observed on D. zibethinus and D. graveolent. Overall, both genes could not describe the genetic relationship among the evaluated durians, and they were grouped in the same cluster in phylogenetic.

Evidence from simulation studies for selective constraints on the codon usage of the Angiosperm psbA gene

The codon usage of the Angiosperm psbA gene is atypical for flowering plant chloroplast genes but similar to the codon usage observed in highly expressed plastid genes from some other Plantae, particularly Chlorobionta, lineages. The pattern of codon bias in these genes is suggestive of selection for a set of translationally optimal codons but the degree of bias towards these optimal codons is much weaker in the flowering plant psbA gene than in high expression plastid genes from lineages such as certain green algal groups. Two scenarios have been proposed to explain these observations. One is that the flowering plant psbA gene is currently under weak selective constraints for translation efficiency, the other is that there are no current selective constraints and we are observing the remnants of an ancestral codon adaptation that is decaying under mutational pressure. We test these two models using simulations studies that incorporate the context-dependent mutational properties of plant chloroplast DNA. We first reconstruct ancestral sequences and then simulate their evolution in the absence of selection on codon usage by using mutation dynamics estimated from intergenic regions. The results show that psbA has a significantly higher level of codon adaptation than expected while other chloroplast genes are within the range predicted by the simulations. These results suggest that there have been selective constraints on the codon usage of the flowering plant psbA gene during Angiosperm evolution.

PPR647 Protein Is Required for Chloroplast RNA Editing, Splicing and Chloroplast Development in Maize

Chloroplasts play an essential role in plant growth and development. Any factors affecting chloroplast development will lead to abnormal plant growth. Here, we characterized a new maize mutant, albino seedling mutant 81647 (as-81647), which exhibits an entirely albino phenotype in leaves and eventually died before the three-leaf stage. Transmission electron microscopy (TEM) demonstrated that the chloroplast thylakoid membrane was impaired and the granum lamellae significantly decreased in as-81647. Map-based cloning and transgenic analysis confirmed that PPR647 encodes a new chloroplast protein consisting of 11 pentratricopeptide repeat domains. Quantitative real-time PCR (qRT-PCR) assays and transcriptome analysis (RNA-seq) showed that the PPR647 mutation significantly disrupted the expression of PEP-dependent plastid genes. In addition, RNA splicing and RNA editing of multiple chloroplast genes showed severe defects in as-81647. These results indicated that PPR647 is crucial for RNA editing, RNA splicing of chloroplast genes, and plays an essential role in chloroplast development.

DNA Barcoding of Two Thymelaeaceae Species: Daphne mucronata Royle and Thymelaea hirsuta (L.) Endl

Daphne mucronata Royle and Thymelaea hirsuta (L.) Endl both belong to the Thymelaeaceae family. Both species are used traditionally to treat several diseases along with various daily applications by Jordanian Bedouins. Traditionally, those species are identified through personal proficiency, which could be misleading due to human errors or lack of expertise. This study aims to investigate an effective DNA barcoding method to identify and characterize Daphne mucronata Royle and Thymelaea hirsuta plant species at the molecular level. Daphne mucronata Royle and Thymelaea hirsuta were collected from the ancient city of Petra in the Southern part of Jordan. Sequences of candidate DNA barcodes were amplified (rbcL, matK, and rpoC1), sequenced, and aligned to the blastn database. Moreover, the obtained sequences were compared with available sequences of related species at the GenBank database. Our results showed that DNA barcoding successfully identifies the two plant species using any of chloroplast genes (rbcL, matK, or rpoC1). The results emphasize the ability of DNA barcoding for identifying and characterizing different plant species through the recruitment of different barcode loci in molecular identification.