Biology subjects

Eves-van den Akker, S.

Publications and source records attributed to Eves-van den Akker, S..

3 recordsLinked to original sources

bioRxiv2018

The genome of the soybean cyst nematode (Heterodera glycines) reveals complex patterns of duplications involved in the evolution of parasitism genes

Heterodera glycines, commonly referred to as the soybean cyst nematode (SCN), is an obligatory and sedentary plant parasite that causes over a billion-dollar yield loss to soybean production annually. Although there are genetic determinants that render soybean plants resistant to certain nematode genotypes, resistant soybean cultivars are increasingly ineffective because their multi-year usage has selected for virulent H. glycines populations. The parasitic success of H. glycines relies on the comprehensive re-engineering of an infection site into a syncytium, as well as the long-term suppression of host defense to ensure syncytial viability. At the forefront of these complex molecular interactions are effectors, the proteins secreted by H. glycines into host root tissues. The mechanisms of effector acquisition, diversification, and selection need to be understood before effective control strategies can be developed, but the lack of an annotated genome has been a major roadblock. Here, we use PacBio long-read technology to assemble a H. glycines genome of 738 contigs into 123Mb with annotations for 29,769 genes. The genome contains significant numbers of repeats (34%), tandem duplicates (18.7Mb), and horizontal gene transfer events (151 genes). Using previously published effector sequences, the newly generated H. glycines genome, and comparisons to other nematode genomes, we investigate the evolutionary mechanisms responsible for the emergence and diversification of effector genes.

genomics↗

bioRxiv2018

Extensive Myzus cerasi transcriptional changes associated with detoxification genes upon primary to secondary host alternation

Aphids are phloem-feeding insects that cause yield losses to crops globally. These insects feature complex life cycles, which in the case of many agriculturally important species involves the use of primary and secondary host plant species. Whilst host alternation between primary and secondary host can occur in the field depending on host availability and the environment, aphid populations maintained as laboratory stocks generally are kept under conditions that allow asexual reproduction by parthenogenesis on secondary hosts. Here, we used Myzus cerasi (black cherry aphid) to assess aphid transcriptional differences between populations collected from primary hosts in the field and those adapted to secondary hosts under controlled environment conditions. Adaptation experiments of M. cerasi collected from local cherry tress to reported secondary host species resulted in low survival rates. Moreover, aphids were unable to survive on secondary host Land cress, unless first adapted to another secondary host, cleavers. Transcriptome analyses of populations collected from primary host cherry in the field and the two secondary host plant species in a controlled environment showed extensive transcriptional plasticity to a change in host environment, with predominantly genes involved in redox reactions differentially regulated. Most of the differentially expressed genes across the M. cerasi populations from the different host environments were duplicated and we found evidence for differential exon usage. In contrast, we observed only limited transcriptional to a change in secondary host plant species.

genomics↗

bioRxiv2018

Shared transcriptional control and disparate gain and loss of aphid parasitism genes and loci acquired via horizontal gene transfer

BackgroundAphids are a diverse group of taxa that contain hundreds of agronomically important species, which vary in their host range and pathogenicity. However, the genome evolution underlying agriculturally important aphid traits is not well understood.\n\nResultsWe generated highly-contiguous draft genome assemblies for two aphid species: the narrow host range Myzus cerasi, and the cereal specialist Rhopalosiphum padi. Using a de novo gene prediction pipeline on both these genome assemblies, and those of three related species (Acyrthosiphon pisum, D. noxia and M. persicae), we show that aphid genomes consistently encode similar gene numbers, and in the case of A. pisum, fewer and larger genes than previously reported. We compare gene content, gene duplication, synteny, horizontal gene transfer events, and putative effector repertoires between these five species to understand the genome evolution of globally important plant parasites.\n\nAphid genomes show signs of relatively distant gene duplication, and substantial, relatively recent, gene birth, and are characterized by disparate gain and loss of genes acquired by horizontal gene transfer (HGT). Such HGT events account for approximately 1% of loci, and contribute to the protein-coding content of aphid species analysed. Putative effector repertoires, originating from duplicated loci, putative HGT events and other loci, have an unusual genomic organisation and evolutionary history. We identify a highly conserved effector-pair that is tightly genetically-linked in all aphid species. In R. padi, this effector pair is tightly transcriptionally-linked, and shares a transcriptional control mechanism with a subset of approximately 50 other putative effectors distributed across the genome.\n\nConclusionsThis study extends our current knowledge on the evolution of aphid genomes and reveals evidence for a shared control mechanism, which underlies effector expression, and ultimately plant parasitism.

genomics↗