Genome assembly of a giant isopod Bathynomus jamesi provides insights
into the body size evolution and adaptation to deep-sea environment
Abstract
Giant isopods are the most representative group of crustaceans living in
the deep sea environment with a huge body size. In order to understand
the genetic basis of these large animals to adapt the harsh oligotrophic
environment of the deep-sea, the genome of a deep-sea (-898 m) giant
isopod Bathynomus jamesi was sequenced and its genome characteristics
were analyzed. The genome assembly of B. jamesi has a total length of
5.89 Gb with a contig N50 of 587.28 Kb, which is among the largest one
with high continuity of the sequenced crustacean genomes. The large
genome size of B. jamesi is mainly attributable to the proliferation of
transposable elements, especially for DNA transposons and CR1-type
LINEs, which account for more than 84% of the genome. A number of
expanded gene families in the genome were enriched in thyroid and
insulin hormone signaling pathways, which might have driven the
evolution of its huge body size. Transcriptomic analysis showed that
several expanded gene families related to glycolysis and vesicular
transport were specifically expressed in its digestive organs, revealing
the molecular mechanism of nutrient absorption and utilization in
oligotrophic environment adaptation. Taken together, the giant isopod
genome provides a valuable resource for understanding the body size
evolution and adaptation mechanisms of macrobenthos to the deep-sea
environment.