Viruses have been infecting everything that lives for millions of years: from bacteria to animals and plants. After all, they just need a host to replicate their genetic material. The stem cells in the shoot tips of plants are an exception. For reasons that are still unclear, viruses cannot multiply in these cells.
Marco Incarbone’s team at the Max Planck Institute for Molecular Plant Physiology in Potsdam-Golm and in Austria has now clarified the molecular background of this mystery. The plant therefore recognizes the virus and releases the alarm hormone salicylic acid. Sensitized in this way, a defense mechanism called RNA interference then specifically hunts down the pathogen’s genetic material and thus eliminates it from the cell.
For their study, which appeared in the journal “PNAS”.the researchers analyzed the buds of the cabbage plant Arabidopsis thaliana under the microscope, even at different stages of virus infection. They intentionally infected their plants with the turnip mosaic virus, which causes cabbage black ring spot on brassicas.
They observed how the virus penetrates the stem cells but is then quickly excluded again. “Surprisingly, these cells are really good at driving out the virus,” says Incarbone: In other tissues, the viruses maraud undisturbed. Why do they escape plant defenses there? “That remains the big question.”
Fighting viruses in the stem cells certainly makes sense from an evolutionary point of view. The entire above-ground plant tissue grows from these cells, including flowers, seeds and thus the next generation of plants. (blk)