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

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.

Keywords: heat-shock protein; hsc70; hsp10; hsp28; hsp70; hsp90; qPCR; thermo-tolerance.

Figure 1

Fold change in Hsp28, Hsp10, Hsp83, Hsp90, Hsp70 and Hsc70cb (mRNA) relative expression levels in A. m. jemenetica (J) and A. m. carnica (C) at the two thermogeographical regions (Riyadh and Baha) and the three foraging times (7:00 a.m.: after ≈ 1 h of foraging; 12:00 p.m.; and 5:00 p.m. (≈1 h before sunset)). Actine was used as endogenous control to calculate ∆ct, and relative expression in A. m. carnica in Baha was used as a reference to calculate the fold change (fold change = 2 ^{ct (reference-treatment)}). Significant fold change difference was determined based on average gene expression of each group using a three-way ANOVA analysis followed by Multiple Student–Newman–Keuls tests. Differences were considered statistically significant at p < 0.05. (*) = significant variation and (ns) = non-significant variation.