Abstract
BackgroundIn insects, hemocyanin superfamily proteins accumulate apparently to serve as sources of amino acids during metamorphosis, reproduction and development. Storage hexamerins are important members of the hemocyanin superfamily. Although insects possess storage hexamerins, very little is known about the character and specific functions of hexamerin 1 and storage protein 1 in insect development.ResultsTo gain insight into the function of storage proteins in insects, cDNAs for two storage proteins were cloned from the fat body of Spodoptera exigua. S. exigua hexamerin 1 (SeHex) cDNA contained an open reading frame of 2124 nucleotides encoding a protein of 707 amino acids with a predicted molecular weight of 82.12 kDa. S. exigua storage protein 1 (SeSP1) cDNA contained an open reading frame of 2256 bp encoding a protein of 751 amino acids with a predicted molecular weight of ~88.84 kDa. Northern blotting analyses revealed that SeHex mRNA is expressed in the fat body, cuticle, midgut and Malpighian tubules and SeSP1 in fat body, Malpighian tubules and tracheae. SeHex and SeSP1 mRNAs were expressed in fat body at different levels from first instar larvae to pupae, with expression was much lower from first instar larvae to first-day fifth instar larvae. SeHex transcript expression was high in fat body of wandering larvae (pre-pupae) and steadily decreased to the seventh pupal day. SeSP1 transcript expression was high in fat body of wandering larvae, 2-day-old fifth instar larvae and 2-, 4- and 7-day-old pupae. SeHex and SeSP1 mRNAs levels were expressed lower than control on the condition of starvation at 12 h. Of insects injected with SeHex and SeSP1 dsRNA, 38.7% and 24.3% survived to 204 h after treatment, respectively. This was significantly lower than in the controls groups.ConclusionsThese findings provide new data on the tissue distribution, expression patterns and the function in starvation of storage proteins. RNA interference results revealed that storage protein genes are key in metamorphosis, reproduction and insect development. The results for SeHex and SeSP1 interference reveal that a potential method to control this pest is to disrupt the regulation of storage proteins.
Highlights
In insects, hemocyanin superfamily proteins accumulate apparently to serve as sources of amino acids during metamorphosis, reproduction and development
It is similar to SP1 genes from T. ni, S. nonagrioides, H. cecropia, Hyphantria cunea, M. sexta, Samia cynthia, Heliconius erato, Bombyx mori, Chilo suppressalis, P. interpunctella, A. aegypti, Culex quinquefasciatus, Anopheles gambiae, Periplaneta americana, Perla marginata, Thermobia domestica, Reticulitermes speratus, A. germari, Sinella curviseta, Tribolium castaneum, Tenebrio molitor and R. flavipes (Figure 2)
Developmental expression of S. exigua hexamerin 1 (SeHex) and S. exigua storage protein 1 (SeSP1) SeHex and SeSP1 mRNAs were expressed in fat body at different levels from fifth instar larvae to pupae
Summary
Hemocyanin superfamily proteins accumulate apparently to serve as sources of amino acids during metamorphosis, reproduction and development. Hemocyanin superfamily proteins accumulate apparently to serve as sources of amino acids during metamorphosis, reproduction and periods when food is. The insect tracheal system has many respiratory proteins that transport oxygen in the hemolymph and, in preparing for metamorphosis, insect larvae store a huge amount of protein in hemolymph [6,7,8,9]. These specialized oxygen-transport proteins evolved from the copper-containing hemocyanins [10]. Storage hexamerins include the hexamerins, juvenile hormone-related protein, riboflavin-binding hexamerin precursor, methionine-rich storage protein (storage protein 1, SP1), very-high-density lipoprotein, tyrosine-rich proteins and hemocyanin-related proteins [4,19]
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