Abstract
BackgroundThe migratory locust, Locusta migratoria manilensis, is an immensely destructive agricultural pest that forms a devastating and voracious gregarious phase. The fungal insect pathogen, Metarhizium acridum, is a specialized locust pathogen that has been used as a potent mycoinsecticide for locust control. Little, however, is known about locust immune tissue, i.e. fat body and hemocyte, responses to challenge by this fungus.MethodsRNA-seq (RNA sequencing) technology were applied to comparatively examine the different roles of locust fat body and hemocytes, the two major contributors to the insect immune response, in defense against M. acridum. According to the sequence identity to homologies of other species explored immune response genes, immune related unigenes were screened in all transcriptome wide range from locust and the differential expressed genes were identified in these two tissues, respectively.ResultsAnalysis of differentially expressed locust genes revealed 4660 and 138 up-regulated, and 1647 and 23 down-regulated transcripts in the fat body and hemocytes, respectively after inoculation with M. acridum spores. GO (Gene Ontology) enrichment analysis showed membrane biogenesis related proteins and effector proteins significantly differentially expressed in hemocytes, while the expression of energy metabolism and development related transcripts were enriched in the fat body after fungal infection. A total of 470 immune related unigenes were identified, including members of the three major insect immune pathways, i.e. Toll, Imd (immune deficiency) and JAK/STAT (janus kinase/signal transduction and activator of transcription). Of these, 58 and three were differentially expressed in the insect fat body or hemocytes after infection, respectively. Of differential expressed transcripts post challenge, 43 were found in both the fat body and hemocytes, including the LmLys4 lysozyme, representing a microbial cell wall targeting enzyme.ConclusionsThese data indicate that locust fat body and hemocytes adopt different strategies in response to M. acridum infection. Fat body gene expression after M. acridum challenge appears to function mainly through activation of innate immune related genes, energy metabolism and development related genes. Hemocyte responses attempt to limit fungal infection primarily through regulation of membrane related genes and activation of cellular immune responses and release of humoral immune factors.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2089-9) contains supplementary material, which is available to authorized users.
Highlights
The migratory locust, Locusta migratoria manilensis, is an immensely destructive agricultural pest that forms a devastating and voracious gregarious phase
59 (13 %) and three (6.5 %) showed significant differential expression in the fat body and hemocytes, respectively, after M. acridum infection. These results reveal the transcriptional responses of the fat body and hemocytes in defense against a locust specific entomopathogenic fungus, and detail immune related genes in the transcriptome of the Orthopteran, L. migratoria manilensis
Illumina sequencing and read assembly Locusts infected with spores of M. acridum and uninoculated insects were used to generate cDNA libraries for examining insect responses to the fungal pathogen
Summary
The migratory locust, Locusta migratoria manilensis, is an immensely destructive agricultural pest that forms a devastating and voracious gregarious phase. The migratory locust, Locusta migratoria manilensis, undergoes a striking behavioral phase transition, from a solitary, essentially harmless animal to a seemingly endless cloud of voracious, traveling swarms that devour the vegetation in their path. The fat body produces most of the proteins and metabolites found in the hemolymph, and acts as the central controller of the synthesis and utilization of energy reserves, i.e. glycogen and lipids [4]. This organ functions to sequester, and release upon appropriate (hormonal) signal, proteins or other molecules required for morphogenesis, egg maturation, and lipid/hormone transport, examples of which include growth factors, vitellogenins, and lipophorins, respectively [5]
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