Genomic evolution and diversity in Botryosphaeriales: insights from pan-genomic and population genetic analyses of representative species

On the Expansion of “Dangerous” Gene Repertoires by Whole-Genome Duplications in Early Vertebrates

It has become a fundamental need to have genome sequence data due to the fact that the basic process of evolution is the change in DNA sequence and genome size. Recent advances in DNA sequencing technology have facilitated the availability of quite a large number of complete genome sequences from simplest prokaryotes to higher eukaryotes. The availability of whole genome sequence data at our fingertips can provide critical insight into how various genomic compositions have contributed to a contemporary understanding of molecular evolution. For this reason, comparative evolutionary genomics has become one of the most rapidly advancing disciplines in the biological sciences. The new generation of comparative genomics offers a powerful aid to studying evolutionary changes among organisms and identifying the genes that are conserved among species, and also the genes that give each organism its own specific characteristics. Informatics related to structural and functional genomics is potentially important in understanding the emergence of new phenotypic characters necessary for the adaptation of organisms. In addition, the evolutionary perspective of genes and genomes is also helpful in understanding disease susceptibility. A large number of scientists from all over the world are involved in determining the genomic underpinnings of morphological, physiological, and behavioral changes. A lot of research has been done to find selection signals on a genome-wide scale, and also focusing on specific gene families to learn more about evolutionary mechanisms. Therefore, it is necessary to compile various current aspects of genomic and evolutionary research at some point. This prompts us to devote a special issue we have named “Comparative Genomics and Genome Evolution”. The series of review articles in this issue of Current Genomics present current advances in multiple areas of comparative genomics and molecular evolutionary studies. This special issue is comprised of eight high quality articles which have been selected through a rigorous reviewing process. Several years ago, with the ground-breaking work of Max D. Cooper and colleagues, an adaptive immune system was discovered in a representative jawless vertebrate (lamprey). The first review article describes concordance and divergence in the immunogenetic architecture between two alternative adaptive immune systems of jawed and jawless vertebrates, and discusses in detail the evolution of the jawless vertebrate immune system on the basis of currently available lamprey genomic resources. In the second review paper, Nikolas Nikolaidis and colleagues discuss the current knowledge on the genomics and evolution of the immunoglobulin mulitigene family in vertebrates. To provide further coverage and discussion of the evolutionary dynamics of multigene families, we commissioned Yoshihito Niimura to review the evolutionary genomics of the olfactory receptor multigene family on a genome-wide scale. The fourth review article presents the interesting scenario of the evolution of mammalian sex chromosomes. Yoko Satta and colleagues reviewed evolutionary aspects related to genomic rearrangements and structures of the sex chromosomes. The next review article, by Arnab Gupta and Svetlana Lutsenko, focuses on the origin and evolution of copper transporting ATPases in eukaryotic organisms. In the sixth article, Mariko Kondo and Koji Akasaka highlight the phylogenetic relationships among echinoderms and the current status of echinoderm genome analysis. The seventh article is related to the evolution of microRNAs. In this article, Zhumur Ghosh and Bibekanand Mallick describe advances of genomics, evolution, and biogenesis of microRNAs. Finally, we conclude with an interesting review article by Chitra Dutta and Sandip Paul on microbial genome signature related to different lifestyles. The authors describe how closely related microbial species are diverged on the basis of the genomic signature of ecological kinship throughout microbial evolution. Recognizing the growing interest in evolutionary genomics, we are happy to present this collection of high quality review articles for this special issue. We would like to thank all of the reviewers for their valuable comments meant to improve the quality of articles. In addition, we offer special thanks to the Editor-in-Chief, and the Current Genomics editorial/production staff, who have contributed invaluably to this project. We hope you find the issue timely, scholarly, and interesting.

An integrated framework for evolution of ciliated protists (Protista, Ciliophora) from the perspective of comparative genomics.

Vibrionaceae is a large marine bacterial family, which can constitute up to 50% of the prokaryotic population in marine waters. Photobacterium is the second largest genus in the family and we used comparative genomics on 35 strains representing 16 of the 28 species described so far, to understand the genomic diversity present in the Photobacterium genus. Such understanding is important for ecophysiology studies of the genus. We used whole genome sequences to evaluate phylogenetic relationships using several analyses (16S rRNA, MLSA, fur, amino-acid usage, ANI), which allowed us to identify two misidentified strains. Genome analyses also revealed occurrence of higher and lower GC content clades, correlating with phylogenetic clusters. Pan- and core-genome analysis revealed the conservation of 25% of the genome throughout the genus, with a large and open pan-genome. The major source of genomic diversity could be traced to the smaller chromosome and plasmids. Several of the physiological traits studied in the genus did not correlate with phylogenetic data. Since horizontal gene transfer (HGT) is often suggested as a source of genetic diversity and a potential driver of genomic evolution in bacterial species, we looked into evidence of such in Photobacterium genomes. Genomic islands were the source of genomic differences between strains of the same species. Also, we found transposase genes and CRISPR arrays that suggest multiple encounters with foreign DNA. Presence of genomic exchange traits was widespread and abundant in the genus, suggesting a role in genomic evolution. The high genetic variability and indications of genetic exchange make it difficult to elucidate genome evolutionary paths and raise the awareness of the roles of foreign DNA in the genomic evolution of environmental organisms.

A comparative study on the genomic and functional diversity of 187 strains of Lactobacillus helveticus

Comparative genomics of the fungal genus Verticillium

Pantoea ananatis is a member of the Enterobacteriaceae family known for its broad host adaptability. This study isolated 10 P. ananatis strains from white spot (MWS)-diseased leaves of maize (Zea mays) grown in Yunnan Province, China, and analyzed their putative functions, genomic diversity, and variation. The inoculation tests revealed that none of the 10 isolates caused MWS symptoms in maize. Nine maize isolates, except for S47, induced a hypersensitive response (HR) in tobacco and caused rot symptoms in onion. Most isolates exhibited plant growth-promoting characteristics, with strains JCC14, JCY1, and S47 significantly enhancing maize seedling growth parameters. Genomic sequencing of 10 maize isolates and two rice isolates revealed that 12 isolates clustered into three groups, with an open pan-genome identified. Ancestral reconstruction indicated that the genome size increased in Group A and then decreased in Group B, with significant gains in orthologous groups at Node 14, the most recent common ancestor (MRCA) of Group A and Group B, and at Node 19, the MRCA of seven maize-isolated strains and other Group B strains. Additionally, 11 single-copy orthologous groups were under positive selection. Furthermore, the HIVir (high virulence, also known as PASVIL, P. ananatis-specific virulence locus) cluster and type VI secretion system-related genes were conserved in certain P. ananatis strains but were not related to their group divergences. This study not only reveals the diverse functions of MWS-diseased maize P. ananatis isolates, but also enhances our understanding of divergent genome evolution and environmental adaptation across P. ananatis species.IMPORTANCEPantoea ananatis is a bacterium commonly found in various agronomic crops. Maize white spot (MWS) has been one of the most destructive diseases affecting maize, leading to significant economic losses. This study clarified that P. ananatis strains colonized maize leaves but were not the causal agents of MWS in Yunnan Province, China. Moreover, most of these P. ananatis strains exhibited plant growth-promoting (PGP) activities, induced hypersensitive response (HR) activity on tobacco, and caused rot symptoms in onion. Notably, the analysis of divergence throughout the evolutionary process revealed significant genomic evolution and environmental adaptation in these P. ananatis strains. This highlights the genetic exchange that has shaped the genome of P. ananatis. These findings improve our understanding of the functional diversity of P. ananatis strains across different hosts and their positions within the evolutionary lineages of P. ananatis species.

Bacterial soft rot of banana, caused by Dickeya zeae, is spreading rapidly in important banana growing areas in China and seriously threatens banana production. In this study, we sequenced the high-quality complete genomes of three typical banana strains, MS1 (size: 4,831,702-bp; genome coverages: 538x), MS_2014 (size: 4,740,000-bp; genome coverages: 586x) and MS_2018 (size: 4,787,201-bp; genome coverages: 583x), isolated in 2009, 2014, and 2018, respectively. To determine their genomic and phenotypic diversity with respect to their hosts of origin, they were compared with other D. zeae strains, including another representative banana strain MS2 from China. The sequenced strains were similar in utilization of carbon source and chemical substrates, and general genomic features of GC content, and tRNA and rRNA regions. They were also conserved in most virulence determinants, including gene-encoding secretion systems, plant cell wall degrading enzymes, and exopolysaccharides. We further explored their genomic diversity in the predicted genomic islands (GIs). These GIs were rich in integrases and transposases, where some genomic dissimilarity was observed in the flagellar gene cluster and several secondary metabolite gene clusters. Different constituents of core biosynthetic modules were found within the bacteriocin and aryl polyene (APE) pigment gene clusters, and the strains from banana showed different phenotypes with respect to antibiosis effects and colony pigmentation. Additionally, clustered regularly interspaced short palindromic repeat (CRISPR) and prophage elements, such as type I-F and III-A CRISPR arrays and an intact prophage of MS1-P5, contributed to bacterial diversity. Phylogenetic tree analysis and genome-genome nucleotide comparison confirmed the genomic divergence among the strains isolated from banana. Considering these characteristics, MS2 and MS_2014 probably diverged later than MS1, while MS_2018 was different and more similar to foreign strains isolated from other hosts in several characteristics. Strain MS_2018 caused severe symptoms on banana varieties previously considered moderately resistant or moderately susceptible, including varieties of Cavendish (Musa AAA) and Plantain (Musa ABB). Our study of genomic and phenotypic diversity raises public attention to the risk of spreading new pathogenic variants within banana growing regions and supports development of predictive strategies for disease control.

Chapter 3 - Genomic Diversity and Evolution of Rhizobia

Genomic diversity and evolution of antibiotic resistance in Yersinia enterocolitica across multiple hosts in eastern China: A 19-year surveillance study.

Rhodococcus equi, a member of the Rhodococcus genus, is a gram-positive pathogenic bacterium. Rhodococcus possesses an open pan-genome that constitutes the basis of its high genomic diversity and allows for adaptation to specific niche conditions and the changing host environments. Our analysis further showed that the core genome of R. equi contributes to the pathogenicity and niche adaptation of R. equi. Comparative genomic analysis revealed that the genomes of R. equi shared identical collinearity relationship, and heterogeneity was mainly acquired by means of genomic islands and prophages. Moreover, genomic islands in R. equi were always involved in virulence, resistance, or niche adaptation and possibly working with prophages to cause the majority of genome expansion. These findings provide an insight into the genomic diversity, evolution, and structural variation of R. equi and a valuable resource for functional genomic studies.

The free-living nematode Caenorhabditis elegans is akey laboratory model for metazoan biology. C.elegans has also become a model for parasitic nematodes despite being only distantly related to most parasitic species. All of the ∼65 Caenorhabditis species currently in culture are free-living, with most having been isolated from decaying plant or fungal matter. Caenorhabditis bovis is a particularly unusual species that has been isolated several times from the inflamed ears of Zebu cattle in Eastern Africa, where it is associated with thedisease bovine parasitic otitis. C.bovis is therefore of particular interest to researchers interested in the evolution of nematode parasitism. However, as C.bovis is not in laboratory culture, it remains little studied. Here, by sampling livestock markets and slaughterhouses in Western Kenya, we successfully reisolated C.bovis from the ear of adult female Zebu. We sequenced the genome of C.bovis using the Oxford Nanopore MinION platform in a nearby field laboratory and used the data to generate a chromosome-scaledraft genome sequence. We exploited this draft genome sequence to reconstruct the phylogenetic relationships of C.bovis to other Caenorhabditis species and reveal the changes in genome size and content that have occurred during its evolution. We also identified expansions in several gene families that have been implicated in parasitism in other nematode species. The high-quality draft genome and our analyses thereof represent a significant advancement in our understanding of this unusual Caenorhabditis species.

Reptiles are notable for the extensive genomic diversity and species richness among amniote classes, but there is nevertheless a need for detailed genome-scale studies. Although the monophyletic amniotes have recently been a focus of attention through an increasing number of genome sequencing projects, the abundant repetitive portion of the genome, termed the “repeatome”, remains poorly understood across different lineages. Consisting predominantly of transposable elements or mobile and satellite sequences, these repeat elements are considered crucial in causing chromosomal rearrangements that lead to genomic diversity and evolution. Here, we propose major repeat landscapes in representative reptilian species, highlighting their evolutionary dynamics and role in mediating chromosomal rearrangements. Distinct karyotype variability, which is typically a conspicuous feature of reptile genomes, is discussed, with a particular focus on rearrangements correlated with evolutionary reorganization of micro- and macrochromosomes and sex chromosomes. The exceptional karyotype variation and extreme genomic diversity of reptiles are used to test several hypotheses concerning genomic structure, function, and evolution.

Gene family expansion analysis and identification of the histone family in Spodoptera frugiperda

Comparative genomics and systems biology offer unprecedented opportunities for testing central tenets of evolutionary biology formulated by Darwin in the Origin of Species in 1859 and expanded in the Modern Synthesis 100 years later. Evolutionary-genomic studies show that natural selection is only one of the forces that shape genome evolution and is not quantitatively dominant, whereas non-adaptive processes are much more prominent than previously suspected. Major contributions of horizontal gene transfer and diverse selfish genetic elements to genome evolution undermine the Tree of Life concept. An adequate depiction of evolution requires the more complex concept of a network or ‘forest’ of life. There is no consistent tendency of evolution towards increased genomic complexity, and when complexity increases, this appears to be a non-adaptive consequence of evolution under weak purifying selection rather than an adaptation. Several universals of genome evolution were discovered including the invariant distributions of evolutionary rates among orthologous genes from diverse genomes and of paralogous gene family sizes, and the negative correlation between gene expression level and sequence evolution rate. Simple, non-adaptive models of evolution explain some of these universals, suggesting that a new synthesis of evolutionary biology might become feasible in a not so remote future.