7 怎 樣煉成的 Story By Roshni Printer crashes the caterpillar's blood sugar level. This tricks the insect’s body into a state of severe starvation, causing a surge in an appetite-stimulating neuropeptide called HemaP. Normally, when an animal has a parasitic infection, its natural defense mechanism is to lose appetite. By fasting, the animal can starve the parasite of the nutrients it needs to multiply [1]. However, the fungus-infected caterpillar feels as though it is starving to death, even though it is continuously eating. The zombie-like hungry insect enters a non-stop feeding cycle. The fungus keeps the host alive long enough to spin itself into an unusually large silk cocoon. Once the silkworm pupates and is no longer useful for gathering food, the fungus finally kills the insect, consuming the massive load of nutrients from the pupa. The fungus then uses that stolen energy to burst bright orange, spore-bearing prongs directly out of the shell of the insect, which are exactly the cordyceps “flowers.” These fruiting bodies release spores into the air to infect more caterpillars. To prove that this metabolic manipulation was a crucial mechanism driven by the trehalase gene of C. militaris, scientists engineered a mutant version of the fungus by deleting the gene [2]. When silkworms were infected with this modified fungus, the caterpillars did not overeat. Their blood sugar also remained stable, and their pupae grew to a completely normal size. By comparing the conditions of the host infected by wild fungus and by this mutant, the researchers proved that it wasn't the caterpillar's body acting out on its own, but instead, it was the single gene working to fatten up the host. The fungus acquired this trehalase gene from insects probably through a process called horizontal gene transfer (HGT) [1, 2]. Unlike typical genetic inheritance, in which genetic information flows vertically from parents to offspring, HGT occurs when genetic material jumps between species. In other words, ancestors of C. militaris managed to “steal” the gene from the insect — likely due to their long-term association, C. militaris somehow absorbed relevant DNA fragments and integrated them into its genome. While this life cycle sounds like horror to the silkworms, the C. militaris harvested is popularly used as a wellness supplement in traditional Chinese medicine for its ability to boost energy, support immunity, and nourish the lungs and kidneys [3–5]. So, the next time you sit down for dinner and find those bright orange "flowers" floating in your soup, take a moment to remember the journey they took to
RkJQdWJsaXNoZXIy NDk5Njg=