By Maryna Mullerman ’20

Doctor Kegan Zhu and researchers from Nanjing University in China investigated the effects of plant microRNAs (miRNAs) on larval development and differentiation in honeybees. The study’s results provide another approach to the understanding of co-evolution of different species and cross-kingdom interactions.

The researchers hypothesized that miRNAs from different sources affected larval development. They recognized that plant miRNAs could be ingested by insects and could accumulate in the body tissues, thus affecting phenotypes. The researchers conducted experiments that involved larval nutrients, such as royal jelly and beebread, pollen, and honey. The researchers characterized the effects of 16 plant RNAs on honeybee development by removing the larvae from a colony and implementing a diet mimicking natural larval food. The scientists analyzed 96 target honeybee genes that could be affected by the plant miRNAs. This gene pool included a stimulatory gene Apis mellifera TOR (amTOR), thought to be responsible for the bee queen’s fate and regulated by a miR162a or plant miRNA that recognized the amTOR gene. The study proceeded to compare the pathways of individual development of the fly Drosophila melanogaster and caste development of Apis mellifera.

The analysis of RNA components of larval food showed that royal jelly and honey contained the most bee miRNAs, while beebread and pollen carried the most plant miRNAs. When the bee larvae were fed with plant miRNAs, their adult versions resembled the morphology of working bees with reduced weights, body sizes, and ovary sizes. Moreover, plant small RNAs and miRNAs prolonged the time of Drosophila melanogaster development and reduced body size, weight, and egg production. The researchers also located a similar miR162a binding site on the Dresophilia melanogaster (dmTOR) gene and suggested that miR162a suppressed dmTOR expression.

The study uncovered that specific plant miRNAs played a big role in working bee development, thereby contributing to the honeybee caste system’s success. The experiment with Drosophila melanogaster provides the basis for an exploration of the shared ancestry of nonsocial and social insects. The study was limited to two well-known species and analyzed a small fraction of existing RNAs, but the results provide new insights into cross-kingdom interactions.

References:

1. K. Zhu, et. al., Plant microRNAs in larval food regulate honeybee caste development. PLOT Genetics 13, (2017). doi: e1006946
2. Image retrieved from: https://www.pexels.com/photo/honeycomb-close-up-detail-honey-bee-56876/