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Identification of Genes Involved in Rapid Cold Hardening of the Tobacco Budworm, Helicoverpa assulta
The tobacco budworm, Helicoverpa assulta, is a freeze-susceptible species that overwinters in temperate zones with pupa diapause. A rapid cold hardening (RCH) and supercooling capacity usually play crucial roles in survival during the overwintering period. This study is performed to identify a cryoprotectant 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. Cryoprotectant analysis using HPLC showed that the preexposure treatment allowed the larvae to accumulate glycerol in the hemolymph. Two genes, glycerol-3-phosphate dehydrogenase (GPDH) and glycerol 3-phosphatase (G3P), that involing in glycerol biosynthesis were identified from the transcriptome of H. assulta 4th instar larvae. From the result of transcriptome, 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 cryoprotectant.
