Expression Levels of Heat-Shock Proteins in Apis mellifera jemenetica and Apis mellifera carnica Foragers in the Desert Climate of Saudi Arabia

SIMPLE SUMMARY: A. m. jemenetica occurs naturally on the Arabian Peninsula and in tropical Africa, and this honeybee subspecies has acquired several morphological, behavioral and molecular adaptations to extreme summer temperatures in Saudi Arabia. In this study, expression levels of different heat-shock protein (hsp) genes in forager A. m. jemenetica (a thermotolerant honeybee subspecies) and A. m. carnica (a thermosusceptible subspecies) were explored and compared under desert and semi-arid climates within Saudi Arabia. The results revealed higher expression levels of hsp mRNAs in A. m. jemenetica compared to A. m. carnica. The expression levels of small- as well as large-molecular-weight heat-shock proteins were higher under desert climate conditions in the Riyadh region compared to the semi-arid conditions in Baha. It is clear that the expression of heat-shock proteins is a key molecular mechanism of A. m. jemenetica adaptation to extreme summer conditions. ABSTRACT: A. m. jemenetica is the indigenous honeybee of the Arabian Peninsula. It is highly adapted to extreme temperatures exceeding 40 °C, yet important molecular aspects of its adaptation are not well documented. In this study we quantify relative expression levels of small- and large-molecular-weight heat-shock proteins (hsp10, hsp28, hsp70, hsp83, hsp90 and hsc70 (mRNAs)) in the thermos-tolerant A. m. jemenetica and thermosusceptible A. m. carnica forager honeybee subspecies under desert (Riyadh) and semi-arid (Baha) summer conditions. The results showed significant day-long higher expression levels of hsp mRNAs in A. m. jemenetica compared to A. m. carnica under the same conditions. In Baha, the expression levels were very modest in both subspecies compared those in Riyadh though the expression levels were higher in A. m. jemenetica. The results also revealed a significant interaction between subspecies, which indicated milder stress conditions in Baha. In conclusion, the higher expression levels of hsp10, hsp28, hsp70ab, hsp83 and hsp90 mRNAs in A. m. jemenetica are key elements in the adaptive nature of A. m. jemenetica to local conditions that enhance its survival and fitness in high summer temperatures.