Pollination, especially insect pollination, plays central roles in maintaining ecological balance. Among those pollinating insects, honey bees are the most valuable species. Worldwide massive death of honey bees in recent years has induced the reduction of agricultural production and loss of biodiversity. The reasons of the death of honey bees mainly includes parasites, viruses and farm chemicals. In Europe and America, the microsporidian parasite Nosema ceranae has been reported as the major death threat of honey bees. Therefore, it is critical to elucidate the pathogenesis of Nosema ceranae infection. 

MicroRNAs (miRNAs) have diverse expression patterns and regulate gene expression in developmental and physiological processes. In 2013, it was reported that miRNAs function as a virulence factor of fungal parasites of plants. To understand the effects of Nosema ceranae infection on honey bee miRNA expression, the research group of Dr. WANG Ruiwu at Kunming Institute of Zoology of Chinese Academy of Sciences conducted a study to deep-sequence honey bee miRNAs and transcriptomes throughout the entire parasite reproduction cycle. 

In this study, the miRNA expressions of the Nosema ceranae spores infected honey bees were monitored at 24 hour intervals for a full 6-day infective cycle. It was found that the expression levels of 17 known miRNAs, which target over 400 predicted genes for degradation, were significantly altered during Nosema ceranae infection. The involved bio-functions include ionic bonding, signal transduction, and regulations of nucleus and trans-membrane transporters.etc.

The results of Enzyme Code analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) database showed that nine bibiological pathways were regulated by these 17 miRNAs. Among them, seven pathways are metabolism related, i.e., the purine metabolism, pyrimidine metabolism and oxidative phosphorylation, amino sugar and nucleotide sugar metabolism.

This study for the first time shows the effects of microsproidian infection on the host miRNA expressions. It elucidates the underlying mechanisms of microsporidian pathogenesis and sheds light on the understanding of host-parasite co-evolution. This study have been published on Scientific Reports.