Involvement of glycerol-3-phosphate dehydrogenase and glycerol 3-phosphatase in rapid cold hardening of the oriental tobacco budworm (Helicoverpa assulta)

A rapid cold hardening (RCH) and supercooling capacity usually play crucial roles in survival during the overwintering period in the oriental tobacco budworm, Helicoverpa assulta, a freeze-susceptible species. This study is performed to identify cryoprotectants as a RCH factor in H. assulta. Pre-exposure of H. assulta larvae to 4°C significantly increased survival at -10°C in all developmental stages from egg to adult. RCH was dependent on the duration of the pre-exposure period. RCH also significantly enhanced the supercooling capacity. Analysis of cryoprotectants from the hemolymph revealed that the pre-exposure treatment allowed the larvae to accumulate glycerol among polyols examined. Glycerol-3-phosphate dehydrogenase (GPDH) and glycerol 3-phosphatase (G3P) that involving in glycerol biosynthesis were identified from the transcriptome of H. assulta 4th instar larvae. Based on the expression level of transcripts, the expressions of GPDH and G3P were relatively increased when compared to that of the control, suggesting that these genes contribute to overwintering and biosynthesis of glycerol.