This article first appeared in Issue 15 of our free digital magazine CURIOUS.
A 5,000-year-old bristlecone pine stands in the White Mountains of California, making it the oldest non-cloned living organism on Earth. We know the extremes of longevity can get messy in the context of animal cancers, but what about botanical species? Do plants get cancer?
Louise Gathercole is the Coordinator for the Centre for Forest Protection (CFP), UK, a new center led by Forest Research and Royal Botanic Gardens Kew, which carries out innovative research into protecting trees and woodlands from future threats. She is also a part-time PhD student researching oak trees. We caught up with her to find out if, and how, plants get sick.
Do plants get sick?
Louise Gathercole (LG): Plants do get sick, and it can have a big impact on things like our food supply. For example, the Irish Potato Famine happened because the plants got sick. With trees, we have had problems with fungi like Dutch elm disease and ash dieback, which have a big impact on our landscape.
What about cancer?
LG: With plants, there are lots of things that cause their cells to grow uncontrollably, and in a way that's not normal for the plant. Usually, these are caused by something else. So, it might be bacteria infecting the cells and subsequently the DNA. You also get viroids, viruses, and fungal infections, and in some cases, we don’t know what’s causing the cell growth.
Then there are also galls caused by gall wasps, a lot of which grow on oak trees. The wasps lay an egg in a leaf or acorn bud and when they hatch, they secrete chemicals that cause the cells of a leaf or an acorn to grow abnormally. That creates this space that's safe for the gall wasps’ larvae to develop in. This doesn’t really harm the tree.
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One of our science leads, Lisa Ward, who is Head of Pathology at Forest Research sent me some examples of plant diseases that cause massive cell proliferation in a cancer-like way. There’s crown gall that transfers bacteria into a plant’s genome, altering levels of plant hormones which leads to irregular cell division, causing tumors to grow. Also, black knot fungus releases chemicals that make the tree grow extra plant cells that are unusually large, resulting in swollen, woody galls. But there are many more.
How do these growths differ from animal cancer?
LG: You don't get secondary cancer because the cells don't move around the body. So, the cancer can't affect the different parts of the plant. But the way these growths can spread is the pathogen itself can move. So, a bacteria might infect cells in one area, but if the bacteria then multiplies and replicates, it can move somewhere else, or get carried somewhere else by another organism.
The other thing is that, for the most part with plants, it’s not spontaneous. It’s often triggered by a bacterium or fungus, while animal cancers are more typically a spontaneous breakdown in DNA replication or a breakdown in the body system that deals with out-of-control cells. Of course, there are exceptions like cervical cancers and human papillomavirus, so there are some similarities there.
Do we have plant medicines?
LG: If you think about agriculture and gardening, there is the use of pesticides and fungicides to protect plants. Then there’s biocontrol, where you might have an invasive insect that could be controlled by introducing more of its natural predators.
That's quite a big area of research now, using biocontrol for potential future threats such as pests and disease, but obviously, you have to do a lot of work to make sure that the predator you’re releasing doesn't affect other species. People are also looking into whether you can put together a cocktail of bacteria that might out-compete a bacterium that's causing problems. Improving the natural environmental conditions, such as soil, can also help as environmental factors can affect a plant’s susceptibility to disease. So, there are lots of things that aren’t quite medicines, but that can actually help to deal with whatever is causing the illness.
What are you looking into at the CFP?
LG: We are researching possible future invasive threats to trees, and also how to make our trees more resilient. We do a lot of genomics research at the CFP at Kew, using methods previously developed for human health or agriculture.
One method is to compare the genomes of sick trees with the trees that seem to be resistant to a pest or disease. If you get more of one version of a gene in the resistant group, that version might be helping the tree to resist the disease. In reality, it is much more complicated than just one gene, but if we can identify the mix of variants, or the genotypes, that lead to a healthier outcome, we can start looking at planting more resistant trees in the future.