Identification of rapid cold hardening-related genes in the tobacco budworm, Helicoverpa assulta

Highlight•Distinguished changes of polyols were found in glycerol and trehalose.•Expression of TPS contributes to the accumulation of trehalose.•Trehalose is responsible for overcoming RCH in Helicoverpa assulta.

A rapid cold hardening (RCH) and supercooling capacity usually play crucial roles in the survival of the tobacco budworm, Helicoverpa assulta, which is a freeze-tolerant species during the overwintering period. Cryoprotectants such as polyols or sugars are known to affect RCH and maintain fluid status of hemolymph improving the survival rate. 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 and also significantly enhanced the supercooling capacity. Analysis of cryoprotectants from the hemolymph revealed that the distinguished changes of polyols were found in the peaks of glycerol and trehalose. As cold treatment was prolonged, the amount of trehalose was continuously increased. In contrast, glycerol showed the highest level at 4 h treatment, and was gradually declined. To understand the pathway of trehalose biosynthesis during the pre-exposure treatment, expression level of genes related to trehalose biosynthesis were analyzed from fat body transcriptome of the 4th instar larvae of H. assulta. Based on the expression level of transcripts, the expression of trehalose phosphate synthase (TPS) harboring TPS and trehalose phosphate phosphatase domain contributes to the accumulation of trehalose in the hemolymph, suggesting that trehalose is responsible for overcoming RCH in H. assulta.

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