Posts Tagged ‘insect’

Genome sequence of the insect pathogenic fungus Cordyceps militaris

March 4th, 2012

Species in the ascomycete fungal genus Cordyceps have been proposed to be the teleomorphs of Metarhizium species. The latter have been widely used as insect biocontrol agents. Cordyceps species are highly prized for use in traditional Chinese medicines, but the genes responsible for biosynthesis of bioactive components, insect pathogenicity and the control of sexuality and fruiting have not been determined.

Chengshu Wang’s group from the Shanghai Institutes for Biological Sciences report the genome sequence of the type species Cordyceps militaries in the last issue of Genome Biology. Phylogenomic analysis suggests that different species in the Cordyceps/Metarhizium genera have evolved into insect pathogens independently of each other, and that their similar large secretomes and gene family expansions are due to convergent evolution. However, relative to other fungi, including Metarhizium spp., many protein families are reduced in C. militaris, which suggests a more restricted ecology. Consistent with its long track record of safe usage as a medicine, the Cordyceps genome does not contain genes for known human mycotoxins. This study shows that C. militaris is sexually heterothallic but, very unusually, fruiting can occur without an opposite mating-type partner. Transcriptional profiling indicates that fruiting involves induction of the Zn2Cys6-type transcription factors and MAPK pathway; unlike other fungi, however, the PKA pathway is not activated.

The data offer a better understanding of Cordyceps biology and will facilitate the exploitation of medicinal compounds produced by the fungus.

Zheng et al. (2011) Genome Biology 12: R116

Photo: Chinese Tussah silkmoth pupae colonized by C. militaris (© Zheng et al.)

The Monarch Butterfly Genome

February 21st, 2012

I know … this paper is not describing the genome of a plant or a fungus, but it is unraveling the 273 Mb genome of the superbe monarch butterfly — a migratory Lepideptora traveling long distance to reach its overwintering grounds in central America. Anyway, Danaus plexippus is interacting with plants and is thus welcome to fly over this blog.

The authors summarized their work as follows:

[We present the draft 273 Mb genome of the migratory monarch butterfly (Danaus plexippus) and a set of 16,866 protein-coding genes. Orthology properties suggest that the Lepidoptera are the fastest evolving insect order yet examined. Compared to the silkmoth Bombyx mori, the monarch genome shares prominent similarity in orthology content, microsynteny,and protein family sizes. The monarch genome reveals a vertebrate-like opsin whose existence in insects is widespread; a full repertoire of molecular components for the monarch circadian clockwork; all members of the juvenile hormone biosynthetic pathway whose regulation shows unexpected sexual dimorphism; additional molecular signatures of oriented flight behavior; microRNAs that are differentially expressed between summer and migratory butterflies; monarch-specific expansions of chemoreceptors potentially important for long-distance migration; and a variant of the sodium/potassium pump that underlies a valuable chemical defense mechanism. The monarch genome enhances our ability to better understand the genetic and molecular basis of long-distance migration.]

Read: Shuai Zhan, Christine Merlin, Jeffrey L. Boore and Steven M. Reppert (2011) The Monarch Butterfly Genome Yields Insights into Long-Distance Migration. Cell 147, 5, 1171-1185.

Figure. Life cycle of the monarch butterfly. Complete metamorphosis from egg to larva (five instars) to pupa (chrysalis) to adult. The male butterfly (upper right) has visible black spots on its hind wings that are missing in females (lower left, underwing view). The larvae feed on milkweed (plants of the genus Asclepias). Photograph of engraving from James Edward Smith, Natural History of the Rarer Lepidopterous Insects of Georgia; from the Observations of John Abbot, 1797.

See also: Monarch Butterfly Genome Begins to Open the Black Box



One Bacterial Cell, One Complete Genome

May 1st, 2010

90% of microbial bugs are eluding current culturing attempts. Sequencing of single cells is a novel culture-independent approach, which enables access to the genetic material of an individual cell of unculturable bacteria. In PLoS One this week, Jan-Fang Cheng’s and Nancy Moran’s groups at JGI and the University of Arizona report the completed sequence of Candidatus Sulcia meulleri, obtained from an uncultured single cell. The Bacteroidetes Sulcia is one of two obligate bacterial symbionts inhabiting sharpshooters. A single Sulcia cell was sampled from the host bacteriome using an inverted microscope (Zeiss) and a micromanipulator, its genome amplified via multiple displacement amplification and sequenced using a combination of Sanger sequence and pyrosequencing, generating a total of 57 Mb of sequence. This approach can now be used to generate complete reference genomes urgently needed for metagenomic of bacterial communities.