Endophyte-Mediated Elicitation Enhances Picrosides Production in Suspension Cultures of Picrorhiza kurroa Royle ex Benth

In the high, thin air of the Himalayas, a small, unassuming herb called Picrorhiza kurroa has long been prized for its ability to heal. For centuries, traditional medicine has relied on its roots to treat liver ailments, asthma, and other conditions. The secret to its power lies in a group of complex chemical compounds called picrosides, which the plant produces as a form of natural defense. However, harvesting these plants from the wild has become a serious problem. The demand for the herb has grown so great that the plant is now endangered, and simply growing it in a garden often fails to produce the same high levels of medicine found in the wild. Scientists have turned to laboratory cultures, growing the plant's cells in flasks, but these cells often forget how to make the valuable chemicals they need. To solve this, researchers are exploring a different strategy: looking at the invisible world of fungi that live inside the plant itself. These microscopic partners, known as endophytes, often help their host plants survive stress and produce more of their medicinal compounds. The question is whether we can use these tiny fungi to teach lab-grown cells how to remember their medicinal purpose.

A team of researchers at the Institute of Himalayan Bioresource Technology in India set out to test this idea using cells from the Himalayan herb. They began by collecting wild specimens of the plant from the Rohtang Pass, a high-altitude region in the Himalayas. From the roots of these wild plants, they carefully isolated three distinct types of fungi living inside the tissue. Using genetic sequencing to identify them, they found two types of Fusarium fungi and one type of Trichoderma. These fungi were not harmful invaders but natural residents of the plant. The scientists then prepared extracts from the fungal cells, creating a liquid solution that contained the chemical signals these fungi naturally release. They took two types of plant cell cultures grown in the lab—one derived from the plant's leaves and the other from its roots—and introduced these fungal extracts to them. The goal was to see if the plant cells would react to the fungal presence by ramping up their production of picrosides and related chemicals.

The experiment involved adding different amounts of the fungal liquid to the plant cell cultures and watching what happened over several days. The researchers found that the plant cells did indeed react, but the response depended heavily on which fungus was used, how much of it was added, and whether the cells came from the leaf or the root. One of the fungi, a species of Fusarium acuminatum, proved to be the most powerful trigger. When the leaf-derived cells were treated with a specific concentration of this fungus, they produced a significant surge in medicinal compounds. The levels of picroside I reached 4.71 milligrams per gram of dry plant weight, picroside II reached 3.93 milligrams, and picroside III reached 0.48 milligrams. The treatment also boosted other important chemicals, including aucubin and catalpol, which are precursors or related compounds that help build the final medicine. The root-derived cells responded well as well, though the exact amounts varied slightly, showing that the plant's different parts react in their own unique ways to the same fungal signal.

The other two fungi also worked, but they acted differently. The Trichoderma species increased the production of picrosides, but not as dramatically as the Fusarium acuminatum. It did, however, show a strong ability to boost the levels of catalpol, a key building block for the plant's chemistry. The third fungus, another Fusarium species, had a more modest effect on the main picrosides but seemed to prefer stimulating the production of precursor chemicals like vanillic acid and cinnamic acid. This suggests that different fungi might be "tuning" the plant's internal chemistry in different directions. The researchers also observed that the timing and concentration mattered greatly. Adding too much of the fungal liquid or leaving it in for too long caused the cells to turn brown and stop growing, indicating that the treatment had become toxic. However, at the right dose, the fungal extract acted like a gentle nudge, waking up the plant's dormant chemical factories without harming the cells.

This study provides a clear demonstration that the microscopic fungi living inside wild plants hold the key to unlocking higher medicinal yields in the lab. By using the natural signals from these fungi, scientists can coax lab-grown plant cells to produce the same high levels of valuable compounds found in their wild counterparts. The research highlights that not all fungi are the same; each species interacts with the plant in a unique way, and finding the right partner is essential. While the work is still in the experimental stage, it offers a promising path forward for conserving the endangered Picrorhiza kurroa. Instead of stripping the mountains of their wild plants, we may soon be able to grow the medicine we need in a controlled environment, guided by the very microbes that have lived alongside the plant for thousands of years.