Genomic analysis of the morphologically simplified endoparasitic crustacean Sacculina carcini
Final Report Abstract
The marine crustacean taxon Rhizocephala (Arthropoda: Multicrustacea: Cirripedia) provide striking examples of extremely modified body structure due to a parasitic life. The adults have lost all the features that are usually associated with arthropods: they grow inside their hosts body as small branching vessels (rootlets), exploiting the host without killing him, but suppressing ecdysis and gonadogenesis, therefore can be defined as parasitic castrators. From time to time an external organ, the breeding sac is formed, bearing the gonads of the parasite. Focussing on Sacculina carcini we provide the first genome assembly of a member of Rhizocephala. The genome is rich in complex and simple repeats (60% of the assembly), making genome assembly a challenge that could only be overcome using long-read sequencing technology. Gene content was compared to the sessile cirriped Amphibalanus amphitrite and other arthropods. While the absolute gene number is well in the range of other crustaceans, the gene turnover between the two cirripedes is higher than between other crustaceans, with many gene family expansions detected also in S. carcini. Gene families were analysed in more detail for transcription factors and peptidases. E.g. the hox gene cluster of S. carcini could be reconstructed almost completely in the genome assembly. Differential gene expression between rootlets and breeding sac show upregulation of e.g. transporters for lipid uptake and two crustacean neurohormones, that are candidates for being agents of host manipulation (orthologs in other species play a role in suppression of ecdysis and gonad development). Surprisingly there is a strongly differential transcriptomic profile between different parts of the rootlet system, hinting to different roles and different types of interaction with host tissue in different sites.
Publications
- (2014) On the origin of adult rootlet organ in parasitic Rhizocephala. Int. Congress of Invertebrate Morphology (ICIM) 3, Berlin, 3.-7.8.2014
Podsiadlowski L
- (2017) Repeat landscapes in the genomes of Cirripedia (Crustacea), DZG-Meeting, Bielefeld 12.-15.9.2017
Martin S, Podsiadlowski L
- (2020) The genome of an endoparasitic crustacean with strongly derived adult morphology: Sacculina carcini. Virt. Symp. Arthopod Genomics 2020; online 21.-24.8.2020
Podsiadlowski L
