Why don’t pandas eat more meat? Molecules found in bamboo may be behind their plant-based diet

Giant pandas have digestive systems that are typical for carnivores. Yet, bamboo is their main source of food. They have evolved several features, for example pseudo thumbs to grasp bamboo and flat teeth that are well suited for crushing it, that make it possible for them to live off plants.

All living organisms have DNA, which stores the genetic information in a cell, and RNA, which carries and transfers this information. MicroRNAs (miRNA) are small non-coding RNAs that play an important role in gene expression, the process of turning the information encoded in a gene into a function. MiRNA from plants can be absorbed through food.

Now, researchers in China have explored if plant-derived miRNA can enter giant pandas’ systems and regulate gene expression and thereby aid adaptation to a bamboo-based diet.  

“We showed that plant-derived miRNAs are present in the blood of giant pandas,” said Dr Feng Li, a researcher at China West Normal University and senior author of the study published in Frontiers in Veterinary Science. “Our study proved that bamboo used as food for giant pandas does affect the change of giant pandas’ feeding habits.”

A matter of taste

The researchers took blood samples from seven giant pandas, including three adult females, three adult males, and one juvenile female. In those samples, they found 57 miRNAs that were likely derived from bamboo.

“MiRNA in bamboo can enter giant pandas’ bodies through diet, be absorbed by the intestine, enter the blood circulation, and then regulate when the giant panda’s RNA transfers information, thus playing a role in regulating the gene expression of giant pandas,” Li explained.

These plant-derived miRNAs can regulate different physiological processes, including growth and development, biological rhythms, behavior, and immune responses.

“MiRNA in bamboo is also involved in the regulation of smell, taste, and dopamine pathways of giant pandas, all of which are related to their feeding habits,” Li said. The researchers believe that as pandas eat more bamboo as they grow, certain miRNAs accumulate, modulate gene expression, and aid in the adaptation to the taste of bamboo. These miRNAs might also influence giant pandas’ sense of smell and enable them to pick out the freshest and most nutritious pieces of bamboo plants. Accordingly, miRNAs from bamboo may facilitate the adaption of giant pandas from a carnivorous to a plant-based diet.

From plant to animals

The researchers also found that pandas with different ages and sexes had different miRNA compositions in their blood. “Only miRNAs that can specifically play a role in regulating gene expression can remain in the body, and those that do not play a role will be expelled,” said Li. For example, some miRNAs regulate reproductive processes and can thus only be found in the blood of pandas of a certain sex or age.

The fact that miRNA could transmit signals from plants to animals, may open doors for studying the treatment and prevention of animal diseases. “Plant miRNAs may also participate in regulating the animal immune system, enhancing animals’ disease resistance,” Li pointed out.

Similarly, studying plant miRNA-induced changes could also help to assess and improve the safety of plant-based foods for animals and humans, the researchers said. However, to draw definitive conclusions about the potential of miRNA in general and the effects it might have on giant pandas, more research is needed.

“The giant panda is a very precious national treasure in our country, and blood samples are not easy to get,” Li concluded. “If possible, we hope to collect blood samples of young pandas who have not yet eaten bamboo for research, and perhaps get more surprising results.”