Two novel soluble trehalase genes cloned from Harmonia axyridis and regulation of the enzyme in a rapid changing temperature.

In previous studies, we have cloned two soluble trehalase genes (HaTreh1-1 and HaTreh1-2) from the harlequin ladybird Harmonia axyridis. Here, we obtained the other two novel genes (HaTreh1-3 and HaTreh1-4) by transcriptome sequencing and rapid amplification of cDNA ends. Generally, anabolism enhancement and catabolism inhibition together contribute to accumulation of trehalose, and trehalase is the key enzyme to start the catabolism of trehalose. To characterize the metabolism of trehalose in H. axyridis and how these trehalase genes are regulated under cold stress conditions, a comparison of trehalose content and trehalase levels in two different rapidly changing temperature environments was carried out to explore the regulation of these genes. We found that an accumulation of trehalose could be observed at 5°C, 0°C and -5°C and trehalase was suppressed in these temperature points during a gradually cooling environment. Then, in a gradually warming environment, trehalose levels increased slightly from -5°C to 15°C and then decreased at 25°C; however, no significant negative association was observed between trehalase and trehalose. Additionally, we found that glycogen could be converted into trehalose to help the individual resist the low temperature. Analysis of the expression of soluble trehalase showed that HaTreh1-1, HaTreh1-2, HaTreh1-3 and HaTreh1-4 were involved in trehalose metabolism; but the gene HaTreh1-4 plays the most important role in the cooling process, and HaTreh1-2 and HaTreh1-4 play the most important role in the warming process. Finally, we found that 5°C might be a temperature signal for H. axyridis; prior to this temperature, individuals must make enough physical preparations to resist cold stress during the winter.