A Chromosome-Level Genome Assembly and Annotation for the Clouded Apollo Butterfly (Parnassius mnemosyne): A Species of Global Conservation Concern

The clouded apollo (Parnassius mnemosyne) is a palearctic butterfly distributed over a large part of western Eurasia, but population declines and fragmentation have been observed in many parts of the range. The development of genomic tools can help to shed light on the genetic consequences of the decline and to make informed decisions about direct conservation actions. Here, we present a high-contiguity, chromosome-level genome assembly of a female clouded apollo butterfly and provide detailed annotations of genes and transposable elements. We find that the large genome (1.5 Gb) of the clouded apollo is extraordinarily repeat rich (73%). Despite that, the combination of sequencing techniques allowed us to assemble all chromosomes (nc = 29) to a high degree of completeness. The annotation resulted in a relatively high number of protein-coding genes (22,854) compared with other Lepidoptera, of which a large proportion (21,635) could be assigned functions based on homology with other species. A comparative analysis indicates that overall genome structure has been largely conserved, both within the genus and compared with the ancestral lepidopteran karyotype. The high-quality genome assembly and detailed annotation presented here will constitute an important tool for forthcoming efforts aimed at understanding the genetic consequences of fragmentation and decline, as well as for assessments of genetic diversity, population structure, inbreeding, and genetic load in the clouded apollo butterfly.

Seq'ing identity and function in a repeat-derived noncoding RNA world

Innovations in high-throughout sequencing approaches are being marshaled to both reveal the composition of the abundant and heterogeneous noncoding RNAs that populate cell nuclei and lend insight to the mechanisms by which noncoding RNAs influence chromosome biology and gene expression. This review focuses on some of the recent technological developments that have enabled the isolation of nascent transcripts and chromatin-associated and DNA-interacting RNAs. Coupled with emerging genome assembly and analytical approaches, the field is poised to achieve a comprehensive catalog of nuclear noncoding RNAs, including those derived from repetitive regions within eukaryotic genomes. Herein, particular attention is paid to the challenges and advances in the sequence analyses of repeat and transposable element-derived noncoding RNAs and in ascribing specific function(s) to such RNAs.

A chromosome-level genome assembly of Pyropia haitanensis (Bangiales, Rhodophyta)

Pyropia haitanensis (Bangiales, Rhodophyta), a major economically important marine crop, is also considered as an ideal research model of Rhodophyta to address several major biological questions such as sexual reproduction and adaptation to intertidal abiotic stresses. However, comparative genomic analysis to decipher the underlying molecular mechanisms is hindered by the lack of high-quality genome information. Therefore, we integrated sequencing data from Illumina short-read sequencing, PacBio single-molecule sequencing and BioNano optical genome mapping. The assembled genome was approximately 53.3 Mb with an average GC% of 67.9%. The contig N50 and scaffold N50 were 510.3 kb and 5.8 Mb, respectively. Additionally, 10 superscaffolds representing 80.9% of the total assembly (42.7 Mb) were anchored and orientated to the 5 linkage groups based on markers and genetic distance; this outcome is consistent with the karyotype of five chromosomes (n = 5) based on cytological observation in P. haitanensis. Approximately 9.6% and 14.6% of the genomic region were interspersed repeat and tandem repeat elements, respectively. Based on full-length transcriptome data generated by PacBio, 10,903 protein-coding genes were identified. The construction of a genome-wide phylogenetic tree demonstrated that the divergence time of P. haitanensis and Porphyra umbilicalis was ~204.4 Ma. Interspecies comparison revealed that 493 gene families were expanded and that 449 were contracted in the P. haitanensis genome compared with those in the Po. umbilicalis genome. The genome identified is of great value for further research on the genome evolution of red algae and genetic adaptation to intertidal stresses.

Transposable Element Genomic Fissuring in Pyrenophora teres Is Associated With Genome Expansion and Dynamics of Host-Pathogen Genetic Interactions

Pyrenophora teres, P. teres f. teres (PTT) and P. teres f. maculata (PTM) cause significant diseases in barley, but little is known about the large-scale genomic differences that may distinguish the two forms. Comprehensive genome assemblies were constructed from long DNA reads, optical and genetic maps. As repeat masking in fungal genomes influences the final gene annotations, an accurate and reproducible pipeline was developed to ensure comparability between isolates. The genomes of the two forms are highly collinear, each composed of 12 chromosomes. Genome evolution in P. teres is characterized by genome fissuring through the insertion and expansion of transposable elements (TEs), a process that isolates blocks of genic sequence. The phenomenon is particularly pronounced in PTT, which has a larger, more repetitive genome than PTM and more recent transposon activity measured by the frequency and size of genome fissures. PTT has a longer cultivated host association and, notably, a greater range of host-pathogen genetic interactions compared to other Pyrenophora spp., a property which associates better with genome size than pathogen lifestyle. The two forms possess similar complements of TE families with Tc1/Mariner and LINE-like Tad-1 elements more abundant in PTT. Tad-1 was only detectable as vestigial fragments in PTM and, within the forms, differences in genome sizes and the presence and absence of several TE families indicated recent lineage invasions. Gene differences between P. teres forms are mainly associated with gene-sparse regions near or within TE-rich regions, with many genes possessing characteristics of fungal effectors. Instances of gene interruption by transposons resulting in pseudogenization were detected in PTT. In addition, both forms have a large complement of secondary metabolite gene clusters indicating significant capacity to produce an array of different molecules. This study provides genomic resources for functional genetics to help dissect factors underlying the host-pathogen interactions.