Gap-free near-T2T genome assembly of Digitalis lanata enables complete enzymatic production of digoxigenin

For centuries, doctors have relied on a powerful heart medicine called digoxin to help failing hearts beat stronger. This drug comes from a plant known as the foxglove, which grows tall spikes of purple flowers. While the medicine has saved countless lives, making it is a difficult and slow process. Farmers must grow the plants, wait for them to mature, and then harvest the leaves to extract the tiny amount of drug hidden inside. The plants grow slowly, and the amount of medicine they produce can change with the weather, making the supply unreliable. Scientists have long wanted to understand exactly how the foxglove plant builds this complex molecule from scratch, hoping that if they could map the steps, they could build the drug in a lab without needing vast fields of plants. The challenge has been that the plant's genetic instructions are hidden inside a massive, tangled library of DNA, and the specific steps to create the final drug have remained a mystery for decades.

A team of researchers has finally unlocked this secret by creating a complete, gap-free map of the foxglove plant's genetic code. By reading the entire instruction manual of the plant, they were able to identify the specific genes responsible for building the drug. They found that the plant uses a series of enzymes, which are tiny biological machines, to transform a simple starting material found in all living things into the complex heart medicine. The researchers successfully gathered these genetic instructions and tested them in a laboratory, proving that they could recreate the entire building process from start to finish. This work not only solves a puzzle that has stumped scientists for sixty years but also opens the door to producing this vital medicine in a sustainable way, free from the limitations of farming.

The journey began with the plant itself, Digitalis lanata, a species of foxglove. The researchers first looked at where the drug components were stored inside the plant. They found that while the raw building blocks were present everywhere, the finished drug components were concentrated mostly in the leaves. This clue told them that the genetic machinery needed to build the drug was likely active in the leaves. To find the specific genes, the team assembled the plant's entire genome, which is the complete set of DNA instructions. This was a monumental task because the plant's DNA is large and filled with repeating patterns that make it hard to read. Using advanced sequencing technology, they managed to piece together the entire genome into 28 complete chromosomes, leaving no gaps. This near-perfect map gave them a clear view of the plant's genetic landscape for the first time.

With the map in hand, the team started looking for the specific genes that act as the builders. They knew that the process starts with cholesterol, a common molecule found in animals and plants. The plant must first chop off a long tail of the cholesterol molecule to make a smaller, more manageable piece. The researchers found two genes that act as the scissors for this job. They then traced the path forward, identifying a series of other genes that add or remove specific chemical groups, reshaping the molecule step by step. Some of these genes act like chemical painters, adding oxygen atoms to specific spots on the molecule to change its shape and function. The team discovered that these genes often sit close together on the chromosomes, suggesting they evolved to work as a team.

One of the biggest mysteries was how the plant adds a specific oxygen group to a difficult spot on the molecule. For years, scientists could not find the enzyme responsible for this step. The researchers used the new genome map to find a candidate gene that was active in the leaves and worked closely with the other known genes. They tested this gene in the lab and confirmed it was indeed the missing piece, a specialized machine that adds an oxygen atom to the correct position. However, when they tried to use this machine on the final stage of the process, it refused to work. The machine was designed to work on the earlier, simpler versions of the molecule, but it could not handle the complex final shape.

To solve this, the researchers looked at the physical structure of the machine using a powerful imaging technique that reveals the shape of proteins at the atomic level. They saw that the machine had a tight pocket where the molecule fits, and the final complex shape of the drug was too bulky to fit inside. By looking at the blueprint of the machine, they identified a single part of the structure that was blocking the entrance. They then made a small change to the gene, swapping one building block of the protein for another to widen the pocket. This simple adjustment allowed the machine to accept the final complex molecule. With this engineered version, the team successfully completed the entire chain of reactions, turning the simple starting material all the way into the final drug component in a test tube.

The result is a complete, step-by-step recipe for building the heart medicine precursor from scratch. The researchers showed that by combining the natural enzymes they found with their newly engineered version, they could produce the drug without ever touching a foxglove plant. This achievement confirms the full path the plant takes to make its medicine and provides a new, reliable way to manufacture it. Instead of waiting for plants to grow, scientists can now use these biological machines to produce the drug in a controlled environment. This breakthrough ensures a steady supply of a life-saving medicine and demonstrates how understanding the genetic code of nature can lead to sustainable solutions for human health.