The Complete Chloroplast Genome Sequencing and Comparative Analysis of Reed Canary Grass (Phalaris arundinacea) and Hardinggrass (P. aquatica)

Complete chloroplast genomes of three wild perennial Hordeum species from Central Asia: genome structure, mutation hotspot, phylogenetic relationships, and comparative analysis

Hordeum L. is widely distributed in mountain or plateau of subtropical and warm temperate regions around the world. Three wild perennial Hordeum species, including H. bogdanii, H. brevisubulatum, and H. violaceum, have been used as forage and for grassland ecological restoration in high-altitude areas in recent years. To date, the degree of interspecies sequence variation in the three Hordeum species within existing gene pools is still not well-defined. Herein, we sequenced and assembled chloroplast (cp) genomes of the three species. The results revealed that the cp genome of H. bogdanii showed certain sequence variations compared with the cp genomes of the other two species (H. brevisubulatum and H. violaceum), and the latter two were characterized by a higher relative affinity. Parity rule 2 plot (PR2) analysis illuminated that most genes of all ten Hordeum species were concentrated in nucleotide T and G. Numerous single nucleotide polymorphism (SNP) and insertion/deletion (In/Del) events were detected in the three Hordeum species. A series of hotspots regions (tRNA-GGU ~ tRNA-GCA, tRNA-UGU ~ ndhJ, psbE ~ rps18, ndhF ~ tRNA-UAG, etc.) were identified by mVISTA procedures, and the five highly polymorphic genes (tRNA-UGC, tRNA-UAA, tRNA-UUU, tRNA-UAC, and ndhA) were proved by the nucleotide diversity (Pi). Although the distribution and existence of cp simple sequence repeats (cpSSRs) were predicted in the three Hordeum cp genomes, no rearrangement was found between them. A similar phenomenon has been found in the cp genome of the other seven Hordeum species, which has been published so far. In addition, evolutionary relationships were reappraised based on the currently reported cp genome of Hordeum L. This study offers a framework for gaining a better understanding of the evolutionary history of Hordeum species through the re-examination of their cp genomes, and by identifying highly polymorphic genes and hotspot regions that could provide important insights into the genetic diversity and differentiation of these species.

Complete Chloroplast Genomes of 14 Subspecies of D. glomerata: Phylogenetic and Comparative Genomic Analyses

Orchardgrass (Dactylis glomerata L.) is a species in the Gramineae family that is highly important economically and valued for its role in ecology. However, the phylogeny and taxonomy of D. glomerata are still controversial based on current morphological and molecular evidence. The study of chloroplast (cp) genomes has developed into a powerful tool to develop molecular markers for related species and reveal the relationships between plant evolution and phylogenetics. In this study, we conducted comparative genomic analyses and phylogenetic inferences on 14 cp genomes of D. glomerata originating from the Mediterranean and Eurasia. The genome size ranged from 134,375 bp to 134,993 bp and exhibited synteny of gene organization and order. A total of 129–131 genes were identified, including 85–87 protein coding genes, 38 tRNA genes and 8 rRNA genes. The cp sequences were highly conserved, and key sequence variations were detected at the junctions of inverted repeats (IRs)/small single–copy (SSC) regions. Moreover, nine highly variable regions were identified among the subspecies based on a sequence divergence analysis. A total of 285 RNA editing sites were detected that were relevant to 52 genes, where rpoB exhibited the most abundant RNA editing sites. The phylogenetic analysis revealed that all Dactylis subspecies clustered into a monophyletic group and most branches provided a high support bootstrap. The main divergence time of D. glomerata was dated to the Miocene era, and this could have been due to changes in the climate. These findings will provide useful insights for further studies on phylogeny, the identification of subspecies and the development of hypotheses for the evolutionary history of the genus Dactylis and of the Gramineae family.

Herbicide Resistance in Phalaris Species: A Review

Weeds, such as Phalaris spp., can drastically reduce the yield of crops, and the evolution of resistance to herbicides has further exacerbated this issue. Thus far, 23 cases of herbicide resistance in 11 countries have been reported in Phalaris spp., including Phalaris minor Retz., Phalaris paradoxa L., and Phalaris brachystachys L., for photosystem II (PS-II), acetyl-CoA carboxylase (ACCase), and acetolactate synthase (ALS)-inhibiting herbicides. This paper will first review the cases of herbicide resistance reported in P. minor, P. paradoxa, and P. brachystachys. Then, the mechanisms of resistance in Phalaris spp. are discussed in detail. Finally, the fitness cost of herbicide resistance and the literature on the management of herbicide-resistant weeds from these species are reviewed.

Complete plastomes of six species of Wikstroemia (Thymelaeaceae) reveal paraphyly with the monotypic genus Stellera

Wikstroemia (Thymelaeaceae) is a diverse genus that extends from Asia to Australia and has been recorded on the Hawaiian Islands. Despite its medicinal properties and resource utilization in pulp production, genetic studies of the species in this important genus have been neglected. In this study, the plastome sequences of six species of Wikstroemia were sequenced and analysed. The plastomes ranged in size between 172,610 bp (W. micrantha) and 173,697 bp (W. alternifolia) and exhibited a typical genome structure consisting of a pair of inverted repeat (IR) regions separated by a large single-copy (LSC) region and a small single-copy (SSC) region. The six plastomes were similar in the 138 or 139 genes predicted, which consisted of 92 or 93 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. The overall GC contents were identical (36.7%). Comparative genomic analyses were conducted with the inclusion of two additional published species of Wikstroemia in which the sequence divergence and expansion of IRs in the plastomes were determined. When compared to the coding sequences (CDSs) of Aquilaria sinensis, five genes, namely, rpl2, rps7, rps18, ycf1 and ycf2, indicated positive selection in W. capitata. The plastome-based phylogenetic analysis inferred that Wikstroemia in its current state is paraphyletic to Stellera chamaejasme, while the ITS-based tree analyses could not properly resolve the phylogenetic relationship between Stellera and Wikstroemia. This finding rekindled interest in the proposal to synonymize Stellera with Wikstroemia, which was previously proposed but rejected due to taxonomic conflicts. Nevertheless, this study provides valuable genomic information to aid in the taxonomic implications and phylogenomic reconstruction of Thymelaeaceae.