families involved in chromatin modification, miRNA synthesis,
and sugar transport.
N Orphan genes comprise 20% of the total number of genes in
the genome. Many are found in EST libraries, suggesting they
are functional.
N As the first genome sequenced for an animal with an ancient
coevolved symbiosis, the pea aphid genome reveals coordination of gene products and metabolism between host and
symbionts. Amino acid and purine metabolism illustrate
apparent cases of biosynthetic pathways for which different
enzymatic steps are encoded in distinct genomes. These
preliminary findings of host-symbiont coordination will be
enhanced by the availability of genomes for three pea aphid
symbionts, including the obligate nutritional symbiont
Buchnera.
N Selenocysteine biosynthesis is not present in the pea aphid, and
selenoproteins are absent.
N Several genes were found to have arisen from bacterial
ancestors. Some of these genes are highly expressed in
bacteriocytes and may function in regulation of the symbiosis
withBuchnera.
N The immune system of pea aphids is reduced and specifically
lacks the IMD pathway; this unusual loss may be linked as a
cause or consequence of the evolution of intimate bacterial
symbioses.
N As a specialized herbivore, the pea aphid must overcome plant
defenses, and the pea aphid genome provides candidates for
genes involved in critical insect-plant interactions.
N The unusual developmental patterns of aphids, involving
extensive polyphenism, may be facilitated by duplications of
many development-related genes.