Characteristics of the glucose-regulated protein 78 (grp78) gene from Bemisia tabaci MED cryptic species and its expression under thermal and nutritional stress conditions

Glucose-regulated protein 78 (GRP78) is a member of the heat shock protein 70 family that is present in the lumen of the endoplasmic reticulum (ER). Although GRP78 acts as an ER chaperone against various stresses in vertebrates, little is known about its role in insects. Herein, we determined the complete sequence of grp78 cDNA from the invasive Bemisia tabaci Mediterranean (MED) cryptic species which is a serious pest of numerous crop plants and examined transcriptional responses to thermal stress treatments and various dietary conditions using quantitative real-time RT-PCR. The grp78 level was increased under the 0 °C and 40 °C treatments for 1 h, but not by the 10 °C or 30 °C treatments. In the experiment of sucrose solution ingestion, the grp78 level was increased proportional to the ingested sucrose amount. When whiteflies were reared with five different plant species (eggplant, paprika, pepper, water melon, and tomato) within the cage, the grp78 level varied according to the plant ingested. The grp78 level was the highest in whiteflies fed on eggplant and lowest in those fed on tomatoes. Overall, our results suggest that grp78 is responsive to strong thermal stress and to the change of sucrose in the diet. This study provides important insights for understanding the role of ER-specific GRP78 in thermal and nutritional physiology of insects at the molecular level.