How Plants Control Honeybee Caste Development

Plant miRNAs from pollen can delay caste differentiation and keep ovaries inactive in honeybee larvae, thereby producing sterile worker bees.

AsianScientist (Sep. 12, 2017) – In a study published in PLOS Genetics, researchers have made the surprising finding than plant microRNAs (miRNAs) in pollen can affect whether honeybee larvae develop into workers or queens.

How caste is formed in honeybees is an enduring puzzle. Although queens and workers are genetically identical, queens are reproductive and have a larger body size, develop faster and live longer than workers. The prevailing view is that differential larval feeding determines caste differentiation: royal jelly stimulates the differentiation of larvae into queen, whereas beebread and pollen consumed by the rest of the larvae lead to the worker bee fate. However, it is still not fully understood how alterations in diet modify so thoroughly the developmental trajectory of honeybees.

Previous research by Professor Zhang Chen-Yu’s group at Nanjing University made the striking finding that plant miRNAs ingested from plant-based foods can pass through the gastrointestinal tract to enter the blood, accumulate in tissues and regulate endogenous gene expression in animals.

Interestingly, since the components of beebread/pollen are mainly plant materials and royal jelly is a glandular secretion of nurse bees, the diets for worker- and queen-destined larvae are differentially derived from plant and animal sources. Therefore, Zhang and colleagues decided to investigate if miRNAs from different larval diets may have distinct impacts on honeybee development.

They found that plant miRNAs are more enriched in beebread/pollen than in royal jelly. When plant miRNAs of beebread/pollen are fed to larvae, they caused developmental delay and reductions in body and ovary size in honeybees. In contrast, miRNAs in royal jelly were not sufficient to reach a functional level, allowing queen-destined larvae to evade this negative regulation.

Mechanistic studies revealed that amTOR, a stimulatory gene in caste differentiation, is the direct target of miR162a. Interestingly, ingested plant miRNAs have a similar inhibitory effect on fruit fly development, even though the fruit fly is not a social insect. These findings suggest that theories about honeybee caste formation need to re-examined and that pollen is specifically collected for its plant miRNAs, the authors said.

The article can be found at: Zhu et al. (2017) Plant MicroRNAs in Larval Food Regulate Honeybee Caste Development.


Source: Nanjing University; Photo: Shutterstock.
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