Organization and potential function of the mrjp3 locus in four honeybee species.

Royal jelly is a nutritious secretion produced by nurse honeybees to provision queens and growing larvae. Major proteins of royal jelly are mutually similar, and they all belong to the MRJP/yellow protein family (pfam03022). The mrjp3 loci in four traditional honeybee species (Apis mellifera, Apis cerana,Apis dorsata, and Apis florea) were sequenced and found to share high sequence and structural similarities. PCR analyses confirmed the presence of an extensive repetitive region, which showed size and sequence polymorphisms in all species. The evolutionary history of mrjp genes and their repetitive regions was reconstructed from their nucleotide sequences. The analyses proved that the repeat region appeared early in the evolution of the mrjp gene family and that the extreme elongation of the repeat is mrjp3 specific. In the MRJPs was documented a correlation between nitrogen content and repeat length. Therefore, it is argued that the repeat occurred due to a selection for an increase in nitrogen storage for a more efficient nutrition of queens and larvae.