NEW YORK (GenomeWeb) – A consortium of more than 110 researchers from across the globe has sequenced and analyzed the genome of the tobacco hornworm sphinx moth.
The moth, Manduca sexta, is a model organism for biochemistry and physiology research, as well as an agricultural pest. As the researchers led by Kansas State University's Michael Kanost reported in Insect Biochemistry and Molecular Biology, they uncovered a high level of macrosynteny in the M. sexta genome and, with additional RNA sequencing data, explored the roles of various gene families in the moth, including in immune response.
"In my laboratory we have been studying the immune system for many years," Kanost said in a statement, "and sequencing the genome has now allowed us to identify almost 600 genes that are likely to be involved in defense against various pathogens."
He and his colleagues sequenced DNA they isolated from a single male M. sexta pupa using the 454 sequencing platform to yield a 419.4 megabasepair genome. At the same time, they performed an RNA-seq analysis of some 52 different libraries, representing a range of tissues and developmental stages including eggs, muscle from larvae, and testes and ovaries from pupae and adults. They estimated that the M. sexta genome houses 15,451 genes.
By comparing it with other Insecta genomes, the researchers noted a high level of macrosynteny in the moth. Through a genome-wide synteny analysis of four clades from three insect orders, they found that some 87 percent of M. sexta genes could be mapped to the silkworm Bombyx mori. In addition, the researchers found that moths and butterflies shared similar amounts of contiguous ancestral regions with the body louse as fruit flies, even though lepidopterans diverged earlier from louse than drosophilids. This suggested that gene rearrangements are less common in lepidopterans, Kanost and his colleagues said.
"In many insects we know that genes often jump around from one location to another in their respective genomes, but in moths and butterflies something seems to be reducing their freedom of movement," co-author Robert Waterhouse from the SIB Swiss Institute of Bioinformatics and the University of Geneva said in the statement.
At the same time, however, when the researchers zoomed in, they noted decreased microsynteny in the M. sexta genome.
The researchers also annotated and investigated a number of gene families and their roles in processes like apoptosis, signal transduction, and immunity in the moth. For instance, they identified 156 putative pattern recognition receptors in the M. sexa genome, including 14 peptidoglycan recognition proteins, four fibrinogen-related proteins, and 76 leucine-rich repeat proteins, among others, that they said likely represent an efficient surveillance system.
They further identified 193 serine protease and serine protease homolog genes in M. sexta. These proteases are activated by pathogen recognition to touch off a cascade that leads to enzyme or cytokine activation. Forty-two of these serine protease and serine protease homolog genes contain one or more amino terminal clip domains, though B. mori only has 24, while Drosophila melanogaster has 37.
They also identified 32 serpin genes, 184 genes that encode members of immune signal transduction pathways, and 86 genes that encode putative antimicrobial pathways. This, Kanost and his colleagues said, indicates that M. sexta contains more immune genes than B. mori.
The M. sexta and its complement of genes will be made publicly available through the US National Agricultural Library.