Three novel trehalase genes from Harmonia axyridis (Coleoptera: Coccinellidae): cloning and regulation in response to rapid cold and re-warming.

Trehalose is the main blood sugar in insects. To study the function of trehalase during exposure to low temperatures, three other novel cDNAs of trehalase were cloned from Harmonia axyridis by transcriptome sequencing and rapid amplification of cDNA ends. One of the cloned cDNAs encoded a soluble trehalase, the second trehalase cDNA encoded a transmembrane-like domain, and the third cDNA encoded a membrane-bound protein. Therefore, these cDNAs were, respectively, named HaTreh1-5, HaTreh2-like, and HaTreh2. HaTreh1-5, HaTreh2-like, and HaTreh2 cDNAs encoded proteins containing 586, 553, and 633 amino acids with predicted masses of approximately 69.47, 63.46, and 73.66 kDa, and pIs of 9.20, 5.52, and 6.31, respectively. All three novel trehalases contained signal motifs "PGGINKESYYLDSY", "QWDYPNAWPP", and a highly conserved glycine-rich (GGGGEY) region. The expression levels of HaTreh1-5 and HaTreh2 mRNAs were high during adult stages, whereas HaTreh2-like was expressed in low amounts in the fourth larval stage. The results showed that the activity of membrane-bound trehalases decreased from 25 to 10 °C and from 5 to - 5 °C during cooling. The results also revealed a decreasing trend in expression of the three HaTreh mRNAs during the cooling treatment, and an initial decrease followed by an increase during the process of re-warming.