Sequencing and de novo assembly of the western tarnished plant bug (Lygus hesperus) transcriptome

Authors: Hull, Joe; Geib, Scott; Walk, Thomas; Fabrick, Jeffrey; Brent, Colin

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2012
Publication Date: 1/24/2013
Citation: Hull, J.J., Geib, S.M., Fabrick, J.A., Brent, C.S. 2013. Sequencing and de novo assembly of the western tarnished plant bug (Lygus hesperus) transcriptome. PLoS One. 8:1.

Interpretive Summary: The western tarnished plant bug is an important pest of numerous fruit, vegetable, and field crops in the western United States. Despite its economic importance, little is known about the basic biology and genetics of this insect. As with all living creatures, genes control not only the growth and development of the western tarnished plant bug, but also how it interacts with its surrounding environment. Genes accomplish this by packaging the basic information for how cells operate into discrete packets known as transcripts, which are essentially blue prints for how cellular components are made. By knowing what transcripts are present, it is possible to infer what cellular components are being produced and their overall importance to the organism at that point in time. A snapshot of the transcripts present in an organism at a particular point in time is known as a transcriptome. To begin to develop a better understanding of how adult western tarnished plant bugs adapt and react to their environment, we examined their transcriptome. We identified more than 19,000 transcripts, the vast majority of which had not been described before for this insect. However, based on comparisons with defined transcripts in other organisms, we were able to assign possible physiological functions to about half of the transcripts. A subset of these transcripts were found to be heat shock proteins, gene products that are essential for survival under various stress conditions such as elevated temperatures. Tests to examine their role in the western tarnished plant bug indicated that the number of transcripts for some of the heat shock proteins was increased in bugs exposed to elevated temperatures. Further exploration of this response may provide clues regarding the mechanisms used by this pest insect to survive the high summer temperatures typical of southern agricultural systems. Our findings provide valuable base-line information that will facilitate research to document and understand the underlying genetics of the western tarnished plant bug. This knowledge is essential to fully understanding how this pest insect interacts with its agricultural environment, and will facilitate the development of improved biologically-based management strategies.

Technical Abstract: Mirid plant bugs are economically important insect pests of many crops worldwide. The western tarnished plant bug Lygus hesperus Knight is a pest of cotton, alfalfa, fruit and vegetable crops, and potentially of several emerging biofuel and natural product feedstocks in the western US. However, little is known about the underlying molecular genetics, biochemistry, or physiology of L. hesperus, including their ability to survive extreme environmental conditions. We used 454 pyrosequencing and de novo assembly to obtain an adult L. hesperus transcriptome consisting of 1,429,818 transcriptomic reads representing 36,131 isotigs that correspond to 19,742 potential unique transcripts. We found that 94% of the publically available L. hesperus sequences were represented in the transcriptome. We further found that 53.7% of the transcriptome exhibited similarity (e-value <= 0.00001) with proteins in the non-redundant protein database. To provide further functional information on the transcriptome, we analyzed sequences for gene ontology (GO) terms, Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations, and potential Pfam domains. To further assess the quality of the transcriptome and to begin to elucidate the molecular basis of the L. hesperus thermal stress response, the transcriptome was scanned for potential heat shock protein (Hsp) homologs. We identified 52 putative Hsp transcripts, a subset of which was sequence verified and their transcriptional response to thermal stress monitored by semi-quantitative PCR. We found that transcripts encoding homologs of Hsp70, Hsp40, and 2 small Hsps were upregulated in the heat-challenged adults, suggesting a role in thermotolerance. The L. hesperus transcriptome advances the underlying molecular understanding of this arthropod pest by significantly increasing the number of available transcripts, and provides the basis for further exploration and understanding of the fundamental mechanisms of abiotic stress responses.