Tiny plant molecules determine if a bee becomes a worker or a queen, and researchers are now wondering how these same molecules impact humans.

Credit: Denis Anderson, CSIRO/Wikimedia Commons

Research during the past five years has shown that plants wield far more power over those who consume them than previously thought. For example, micro RNAs (miRNAs) ingested from plants can pass through an individual’s gastrointestinal tract, enter the blood stream, accumulate in tissues, and regulate gene expression. In short, these tiny molecules can affect the very essence of the consumer.

To better understand the phenomenon, scientists chose to investigate how miRNAs influence the development of the ultimate plant-lovers — honeybees — and were amazed by what they witnessed.
 
Honeybee larvae that consumed miRNA-rich “beebread” — a bee-made food consisting primarily of pollen, honey, and enzymes — experienced delayed development that kept their ovaries inactive. These females became worker bees.
The single reproductive female in hives — aka the queen bee — instead feasted on royal jelly secreted by the glands of nurse bees. With few miRNAs in this food, the queen’s ovaries remained active, allowing her to reproduce big time after mating.
 
The findings, published in the journal PLOS Genetics, provide evidence for the newly identified form of gene control. Senior author Xi Chen of Nanjing University described it as “cross-kingdom regulation of animal genes by dietary plant miRNAs.” This refers to the taxonomic grouping of species, with animals, plants, and fungi being three of the separate kingdoms.
 
 “Transfer of miRNAs from one species to another may be a conventional mechanism to facilitate crosstalk and interspecies communication,” Chen added.
 
“Crosstalk” refers to how molecules can interact and affect each other.

Credit: Emma Mullen

Chen brought honeybees into his lab, where he and his colleagues fed bee larvae simulated beebread supplemented with plant miRNAs. As predicted, they developed more slowly and had smaller bodies and ovaries than larvae fed food without the supplements. They grew up to be workers.
 
Chen and his team then conducted a similar experiment on fruit fly larvae. Plant miRNAs had a similar effect on the flies, even though they are not social insects divided into castes, or group ranks.
 
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MiRNA presence in plants is itself subject to a number of influences. “The abundance of miRNAs will respond to environmental cues,” Chen said. “Moreover, miRNA levels will also change in different developmental stages, such as from vegetative growth to reproduction.”
 
The entire natural system shows how deeply intertwined plants are to their environments and bees are to plants, with each player having a profound impact on the other.

Credit: Xi Chen and Kegan Zhu

In recent years, honeybee populations worldwide have dramatically declined, threatening agriculture. One possible cause could be the foods that beekeepers are giving their charges.
 
“Now artificial pollen substitutes — commonly consisting of protein sources derived from soy, wheat or lentils — are widely used as nutrition supplements in agricultural systems,” Chen said. “Although the supplemental protein diets offset the poor nutritional conditions in honeybee colonies, long-term consumption of protein as the sole nutrient may compromise the ability of plant miRNAs to fine-tune honeybee development.”
 
Prior research has also shown that artificial pollen substitutes were not sufficient to boost a bee’s cellular immunity against parasitic infections. Given these determinations, the researchers now advise beekeepers not to use artificial pollen substitutes as the sole diet for their bees.
 
RELATED: Insecticide Alters Honeybee Genes
 
The impact of plant miRNAs on bees is so powerful that it might have even affected their evolution into social insects. Chen explained that the ancestors of bees were likely burrowing wasps that lived in the middle Cretaceous Period, when non-avian dinosaurs were still in existence. As flowering plants emerged during the Tertiary Period (2.6-66 million years ago) so too did the social behavior among bees.
 
Chen said that microRNAs also can influence human gene expression.

“However,” he added, “it doesn’t necessarily mean that pollen miRNAs will also inhibit ovary development or fertility in humans. For one thing, unlike honeybees, pollen is not the major food source for humans, hence ingested pollen microRNAs would be well below the amount required for any physiological effect.”
 
Studies on hunter-gatherer diets, however, find that our ancestors for tens of thousands of years often included numerous vegetables, fruits, and starches — such as tubers — in their diets. They additionally frequently consumed a lot of honey, as did the ancient Egyptians and other early cultures.

Credit: Keith Schengili-Roberts/Wikimedia Commons

“Compared to beebread, there are fewer miRNAs in honey,” Chen said. “Therefore, it is more likely to be the sugars or other natural ingredients in honey that may be beneficial to human health.”
 
Future research could help to answer that question, along with many others posed by the new research.
 
Chen said that he and his colleagues are not certain what precise underlying mechanism allows for the changes that miRNAs exert over honeybees. The researchers look forward to collaborating with bee experts and ecologists to further explore how honeybees and plants have co-evolved over the millennia.
 
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