Expression of cs, ast, alt and ldh genes during diapause of the european corn borer Ostrinia nubilalis (Hbn.)

Abstract

Many insect species overcome unfavourable environmental conditions by entering diapause, a type of hypometabolic resting state which features accumulation of energy reserves, lowered oxidative metabolism rates, synthesis of protective metabolites and expression of specific genes. In order to better understand the changes occuring at the transcriptional level during diapause of the economically important European corn borer Ostrinia nubilalis (Hbn.), the expression of genes encoding selected metabolic enzymes was measured in this study. The selected enzymes are markers of aerobic (citrate synthase, aspartate aminotransferase, alanine aminotransferase) and anaerobic metabolism (lactate dehydrogenase). Total RNA was isolated from whole-body non-diapausing (ND) and diapausing (D) 5th instar larvae acclimated to different temperatures (15°C, 5°C, –3°C, – 16°C) due to a close link between diapause and cold hardiness in this species. QPCR was performed and relative gene expression was determined using rps3 as the reference gene and the ND group as control. Relative expression of cs gene did not differ between groups, suggesting that this enzyme is regulated posttranslationally. Relative expressions of ast and alt genes were significantly higher in the ND group compared to diapausing larvae, while the expression of ldh was higher in the diapausing groups. A temperature effect on relative gene expression of cs, ldh and alt was determined. Higher cs expression was recorded in diapausing larvae acclimated to 5°C compared to D(15°C), probably compensating for lowered CS enzyme activity. Cold acclimation leads to higher expression of ldh in diapausing larvae, especially in D(–3°C) group, as expected. Lastly, acclimating diapausing larvae to 5°C and –3°C resulted in higher expression of alt in these groups compared to D(15°C) larvae, leading to an increase of the cryoprotective alanine synthesis.