Table of Contents
The Hessian fly (HF, Mayetiola destructor) is a pest of wheat (Triticum spp.), and a member of a large dipteran family (the gall midges, Cecidomyiidae). Its genetics and behavior are representative of several other important plant-galling pests . The HF probably evolved with wheat in the Fertile Crescent. It was perhaps the first invasive insect pest in the United States .
HF adults do not feed and live for less than 3 days. Adult females mate only once and deposit 100 – 300 eggs between the lengths of wheat leaves . The small reddish embryos usually require 4 days to fully develop. Neonate first-instar larvae crawl down the leaf after hatching and settle under the leaves at the joints of the stem or the base of the seedling. There, they attack the epidermal cells of developing leaf tissue. HF larvae are plant-galling parasites. First-instar larvae induce the formation of plant nutritive tissue and alter plant development . The plant then becomes a nutritive sink that feeds the second-instar larvae. This transformation stunts plant development and reduces both grain quantity and grain quality . When larvae feed on wheat seedlings, the shoots they are directly feeding on eventually die and produce no grain. Third-instar larvae do not feed and pass the winter in diapause. HF control typically relies upon the cultivation of resistant wheat varieties, which carry one or more major dominant HF-resistance genes. The HF has a relatively small genome (~158 Mb) composed of two autosomes (A1 and A2) and two X chromosomes (X1 and X2) . Like other gall midges, HF cytogenetics and sex determination is characterized by chromosome imprinting and chromosome elimination events. Females are diploid for all four chromosomes (A1A2X1X2/A1A2X1X2) and males are diploid for the autosomes, but haploid for the X chromosomes (A1A2X1X2/A1A2OO). Polytene chromosomes are present in the larval salivary glands . Genetic recombination occurs only in females, and males transmit only their mother’s chromosomes to their offspring. Chromosome elimination during embryogenesis determines the sex of the embryo. Embryos that eliminate the paternally inherited X chromosomes develop as males. Embryos that retain the paternally inherited X chromosomes develop as females. Embryonic chromosome elimination is usually maternally controlled, and therefore, the offspring of individual females are either all female or all male. Investigations of the HF genome have focused on the HF-wheat interaction [7-9], the genetic response of the HF to HF-resistance genes in wheat [10-12], and the unusual cytogenetics of the insect .
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6. Aggarwal, R., et al., A BAC-based physical map of the Hessian fly genome anchored to polytene chromosomes. BMC Genomics, 2009. 10: p. 293.
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8. Williams, C.E., et al., Induced epidermal permeability modulates resistance and susceptibility of wheat seedlings to herbivory by Hessian fly larvae. Journal of experimental botany, 2011.
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- Analysis Name
- Mayetiola destructor whole genome assembly v1
- Baylor HGSC (NA)
- Date performed
- Materials & Methods
- The Mdes_1.0 release was based on the assembly of whole genome shotgun reads with the 454 Newbler assembler (v2.1-PreRelease-5/13/2009). Reads from each Newbler scaffold were grouped with any missing pairs, and reassembled using Phrap in an attempt to close the gaps within the Newbler scaffold. In a second round of gap filling, Illumina reads were mapped to sequences next to the gaps in the Newbler scaffolds. For each gap, the mapped Illumina reads and corresponding mate-pairs were extracted and reassembled using Phrap. The Phrap contigs were used where possible to close small gaps. Then, Sanger BAC end sequences were used to further build the scaffolds. Finally the scaffolds were mapped using BAC end sequences and placed on chromosomes using the FPC map.
- Contig N50
- Scaffold N50
- GC Content