Pinna nobilis RNA-Seq and Transcriptome

With the intensification of maritime traffic, recently emerged infectious
diseases have become major drivers in the decline and extinction of
species. Since 2016, mass mortality events have decimated the endemic
Mediterranean Sea bivalve Pinna nobilis, affecting ca.
100% of individuals. These events have largely been driven
by Haplosporidium pinnae’s infection, an invasive species which
was likely introduced by shipping. While monitoring wild populations
of P. nobilis, we observed individuals that survived such a mass
mortality event during the summer of 2018 (France). We considered these
individuals resistant, as they did not show any symptoms of the disease,
while the rest of the population in the area was devastated. Furthermore,
the parasite was not detected when we conducted a PCR amplification of a
species-specific fragment of the small subunit ribosomal DNA. In parallel,
the transcriptomic analysis showed evidence of some parasite RNA
indicating that the resistant individuals had been exposed to the parasite
without proliferating. To understand the underlying mechanisms of
resistance in these individuals, we compared their gene expression with
that of susceptible individuals. We performed de novo transcriptome
assembly and annotated the expressed genes. A comparison of the
transcriptomes in resistant and susceptible individuals highlighted a gene
expression signature of the resistant phenotype. We found significant
differential expressions of genes involved in immunity and cell
architecture. This data provides the first insights into how individuals
escape the pathogenicity associated with infection.