Overexpression of Bmhsp19.9 protects BmE cells and transgenic silkworm against extreme temperatures

Temperature stress disrupts protein homeostasis in biological cells. High temperature causes death of the silkworm Bombyx mori, while low temperature leads to slow growth of silkworm in sericulture. Small heat shock proteins (sHsps) play a crucial role in maintaining protein homeostasis and protecting cells against various harmful conditions. In this study, the expression patterns of Bmhsp19.9 were analyzed by reverse transcription (RT)-PCR and quantitative PCR. The promoters hsp19.9P1 and hsp19.9P2 of Bmhsp19.9 were cloned, quantitative PCR and western blotting confirmed that the longer promoter of hsp19.9P1 showed higher activity compared to hsp19.9P2. Overexpression of Bmhsp19.9 increased the viability of BmE cells at high temperatures. The transgenic vector pb-H19.9 was constructed, in which Bmhsp19.9 was overexpressed under the control of hsp19.9P1. Two transgenic lines, H19.9A and H19.9B, were generated via microinjection of P50 silkworm embryos. Quantitative PCR and western blotting revealed that the content of Bmhsp19.9 in transgenic silkworms was higher than that in the control. After exposure to 35 °C for 49 h, the survival rate was increased by approximately 40% in transgenic silkworms compared to non-transgenic P50. When P50 and H19.9A were reared at 13 °C, growth was faster and the survival rate and surviving larval weight were significantly higher in H19.9A compared to P50. These results suggest that overexpression of Bmhsp19.9 increased the resistance of transgenic silkworms to extreme temperatures, which may be useful for sericulture in regions and seasons with no optimal average temperatures for silkworm.