Genomes of two millipede species shed light on their evolution,
development and physiology

Date:
September 29, 2020
Source:
PLOS
Summary:
Researchers have sequenced and analyzed complete genomes from two
very different millipede species. The study provides important
insights into arthropod evolution, and highlights the genetic
underpinnings of unique features of millipede physiology.



FULL STORY ========================================================================== Millipedes, those many-legged denizens of the soil surface throughout the world, don't always get the recognition they deserve. But a new study by
Jerome Hui of Chinese University of Hong Kong and colleagues puts them in
the spotlight, sequencing and analyzing complete genomes from two very different millipede species. The study, publishing on September 29th in
the open-access journal PLOS Biology, provides important insights into arthropod evolution, and highlights the genetic underpinnings of unique features of millipede physiology.


========================================================================== Millipedes and centipedes together comprise the Myriapoda -- arthropods
with multi-segmented trunks and many legs. Centipedes sport one pair
of legs per segment, while millipedes bear two. Despite the apparent
numeric implications of their names, different centipede species bear
between 30 and 354 legs, and millipedes between 22 and 750. There are
about 16,000 species of myriapods, including over 12,000 species of
millipedes, but only two myriapod genomes have so far been characterized;
a complete genome for the centipede Strigamia maritima, and a rough
"draft" sequence of a millipede genome.

The authors of the new study fully sequenced the genomes of two millipede species, the orange rosary millipede Helicorthomorpha holstii, and
the rusty millipede Trigoniulus corallinus, from two different orders,
each distributed widely throughout the world. They also analyzed the
gene transcripts (transcriptomes) at different stages of development,
and the proteins (proteomes) of the toxin-producing "ozadene" glands.

The researchers found that two species have genomes of vastly different
sizes - - the orange rosary's genome is 182 million base pairs (Mb), while
the rusty's is 449 Mb -- which the authors showed was due mainly to the
rusty millipede's genome containing larger non-coding regions (introns)
within genes and larger numbers of repetitive "junk" DNA sequences.

Homeobox genes play central roles in body plan formation and segmentation during animal development, and the authors found lineage-specific
duplications of common homeobox genes in their two species, which
differed as well from those found in the previously published millipede
genome. None of the three, however, displayed the massive duplications
seen in the homeobox genes in the centipede genome. They made further discoveries about the organization and regulation of the homeobox genes
as well.

Many millipedes bear characteristic glands on each segment, called
ozadene glands, which synthesize, store, and secrete a variety
of toxic and noxious defensive chemicals. The authors identified
multiple genes involved in production of these chemicals, including
genes for synthesizing cyanide, as well as antibacterial, antifungal,
and antiviral compounds, supporting the hypothesis that ozadene gland secretions protect against microbes as well as predators.

The results of this study provide new insights into evolution of the
myriapods, and arthropods in general. "The genomic resources we have
developed expand the known gene repertoire of myriapods and provide a
genetic toolkit for further understanding of their unique adaptations
and evolutionary pathways," Hui said.


========================================================================== Story Source: Materials provided by PLOS. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Zhe Qu, Wenyan Nong, Wai Lok So, Tom Barton-Owen, Yiqian Li,
Thomas C. N.

Leung, Chade Li, Tobias Baril, Annette Y. P. Wong, Thomas Swale,
Ting- Fung Chan, Alexander Hayward, Sai-Ming Ngai, Jerome
H. L. Hui. Millipede genomes reveal unique adaptations during
myriapod evolution. PLOS Biology, 2020; 18 (9): e3000636 DOI:
10.1371/journal.pbio.3000636 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200929152154.htm

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