A dual sensing mechanism of eastern honeybee Apis cerana that upregulates the expression level of chemosensory protein CSP1 and enhances the binding affinity to loquat floral volatiles at low temperature

Abstract

As a native bee species, the eastern honeybee (Apis cerana) plays an essential role in pollinating loquat flowers, which bloom in early winter in China. This pollination behavior is closely related to A. cerana's ability to adapt to low temperatures, which depends on the functionality of its chemoreceptive system. Transcriptome analysis revealed a significant upregulation of the A. cerana chemosensory protein 1 (CSP1) gene at low temperatures. Fluorescence competitive binding experiments indicated that nine chemical volatiles from loquat flowers exhibited a stronger binding affinity to CSP1 than to odorant binding protein 2 (OBP2). Thermodynamic analysis revealed that CSP1's binding affinity increases at low temperatures, with a static binding mechanism largely influenced by the specific volatile molecule rather than the type of olfactory soluble protein. Molecular docking and site-directed mutagenesis confirmed that F44 residue may play a key role in CSP1's binding to three primary volatile compounds. In summary, the present study identified a dual sensing mechanism in which low temperatures upregulated the expression of CSP1 and enhanced the binding affinity of CSP1 to loquat flower volatiles. These findings not only clarify A. cerana's chemoreceptive mechanism toward loquat flower volatiles in pollination but also provide a theoretical basis for further exploring ecological adaptations between native bees and early-winter flowering plants.