Cowpea bruchid midgut transcriptome response to a soybean cystatin – costs and benefits of counter‐defence

Abstract

The insect digestive system is the first line of defence protecting cells and tissues of the body from a broad spectrum of toxins and antinutritional factors in its food. To gain insight into the nature and breadth of genes involved in adaptation to dietary challenge, a collection of 20 352 cDNAs was prepared from the midgut tissue of cowpea bruchid larvae (Callosobruchus maculatus) fed on regular diet and diets containing antinutritional compounds. Transcript responses of the larvae to dietary soybean cystatin (scN) were analysed using cDNA microarrays, followed by quantitative real-time PCR (RT-PCR) confirmation with selected genes. The midgut transcript profile of insects fed a sustained sublethal scN dose over the larval life was compared with that of insects treated with an acute high dose of scN for 24 h. A total of 1756 scN-responsive cDNAs was sequenced; these clustered into 967 contigs, of which 653 were singletons. Many contigs (451) did not show homology with known genes, or had homology only with genes of unknown function in a Blast search. The identified differentially regulated sequences encoded proteins presumptively involved in metabolism, structure, development, signalling, defence and stress response. Expression patterns of some scN-responsive genes were consistent in each larval stage, whereas others exhibited developmental stage-specificity. Acute (24 h), high level exposure to dietary scN caused altered expression of a set of genes partially overlapping with the transcript profile seen under chronic lower level exposure. Protein and carbohydrate hydrolases were generally up-regulated by scN whereas structural, defence and stress-related genes were largely down-regulated. These results show that insects actively mobilize genomic resources in the alimentary tract to mitigate the impact of a digestive protease inhibitor. The enhanced or restored digestibility that may result is possibly crucial for insect survival, yet may be bought at the cost of weakened response to other stresses.

Transcriptional Analysis of The Adaptive Digestive System of The Migratory Locust in Response to Plant Defensive Protease Inhibitors

“…This is the first time that this type of compensation is observed in L. migratoria . Partial reliance on insensitive proteases as counter defence however has already been observed in different other insects, including: Helicoverpa armigera, Spodoptera exigua , Callosobruchus maculatus, Leptinotarsa decemlineata and Schistocerca gregaria 914162728. Our findings confirm that regulating the expression of proteolytic enzymes is a common strategy applied by insects to evade loss of proteolytic activity caused by the presence of PI in the gut.…”

“…Like in other insects, the underlying regulatory mechanisms of this adaptation are however still unknown. Up to now, only few studies have tried to identify broader transcriptional changes associated with this phenomenon81415161718. However, these studies mostly investigated long-term changes after dietary PI uptake and did not focus on the initial driving forces regulating the response.…”

Plant Defense Inhibitors Affect the Structures of Midgut Cells in Drosophila melanogaster and Callosobruchus maculatus

“…The control pellets were made using a standard protocol 26. The dose was chosen based on preliminary experiments.…”

“…Even though information on larval cross-section through the proventriculus has been recorded earlier as part of the research on the digestive system,25 we found no study on the microstructure of midgut cells in D. melanogaster. C. maculatus is a coleopteran pest of stored cowpea seeds and those of other grain legumes 26. The ultrastructure of midguts of several other insects has been described 27.…”

Digestive proteases in bodies and faeces of the two-spotted spider mite, Tetranychus urticae

“…Polyphagous herbivorous are expected to be exposed to a broad array of defense proteins of plant origin, representing their digestive enzymes the first-line of defenses to deal with these noxious plant proteins. In the case of phytophagous insects, it is established that the success to cope with plant defense proteins depends on the regulation of complex multigene families of digestive enzymes (Bown et al, 1997;Chougule et al, 2005;Chi et al, 2009). Indeed, insect feeding on plants are adapted to circumvent the adverse effects of plant protease inhibitors by the up-regulation of targeted proteases, the induced expression of novel insensitive proteases, and/or the proteolytic degradation of protease inhibitors (Jongsma and Bolter, 1997;Ortego, 2012).…”