Abstract:

【Aim】 In the previous studies it was found that the learning ability of Apis mellifera ligustica worker bees treated with imidacloprid is decreased, and transcriptomic analyses showed that the expression of major royal jelly protein 1 gene Mrjp1 is significantly down-regulated in the brains of bees treated with imidacloprid, suggesting that MRJP1 may be involved in olfactory learning in honeybees. This study aims to verify the crucial role of MRJP1 in olfactory learning in A. mellifera ligustica workers through silencing Mrjp1 by RNA interference (RNAi). 【Methods】 The cDNA sequence of Mrjp1 was obtained by cloning technique and validated by sequencing, and then the sequence was used for designing primers for generating dsRNA for knockdown of Mrjp1 by RNAi. The worker bees of A. mellifera ligustica injected with dsMrjp1 were assigned to the treatment group (dsMrjp1-injected group), and those injected with dsEGFP were assigned to the control group (dsEGFP-injected group). Then, the olfactory learning and memory abilities of the two groups were compared based on the proboscis extension response (PER) assay. Finally, the relative expression level of Mrjp1 in the brain of A. mellifera ligustica workers after injection of dsMrjp1 was detected by quantitative realtime PCR (qRT-PCR). 【Results】There was a significant difference in the learning ability of A. mellifera ligustica workers between the dsMrjp1injected group and the dsEGFP-injected group, with the learning ability of the dsMrjp1-injected group significantly decreased. However, there was no significant difference in the faculty of memory of A. mellifera ligustica workers at 2 h after learning between the two groups. The qRT-PCR results showed that the expression level of Mrjp1 in the brain of A. mellifera ligustica workers in the dsMrjp1-injected group was significantly lower than that in the dsEGFP-injected group, indicating that A. mellifera ligustica workers with decreased learning ability correspondingly exhibit lower expression level of Mrjp1. 【Conclusion】 After knockdown of Mrjp1 by RNAi, the olfactory learning performance of A. mellifera ligustica workers is significantly decreased, while their memory performance is not significantly affected, suggesting that Mrjp1 is probably one of the key genes regulating learning in A. mellifera ligustica. The results of this study contribute to further understanding of the molecular mechanism related to olfactory learning in honey bees.

Key words: Apis mellifera ligustica, major royal jelly protein, RNA interference, olfactory learning, memory, proboscis extension response