How Pine Trees Fight Back

Have you ever wondered how trees defend themselves against disease? Unlike humans, who rely on immune cells to fight infection, plants depend on specialised defence proteins to recognise harmful microbes, or pathogens. A recent study reveals that some of the defence-triggering proteins used by plants to recognise invaders are shared across completely different types of pine pathogens.

Pine trees, such as Pinus radiata, face attacks from many pathogens. This study focused on three major threats:

• Dothistroma septosporum ,  a fungus that causes Dothistroma needle blight
• Cyclaneusma minus ,  another fungus responsible for Cyclaneusma needle cast
• Phytophthora pluvialis ,  an oomycete (a fungus-like organism, but evolutionarily distinct from fungi) that causes red needle cast

These pathogens secrete molecules called effector proteins, which aim to weaken the tree’s defences and help the pathogen colonise the plant. However, pine trees can sometimes detect these effectors and activate an immune response to stop the infection.

Even though these pathogens come from different biological kingdoms, researchers discovered that they share similar effector proteins that can trigger immune responses in pine trees. One key protein caused cell death in pine needles, an extreme defensive response that prevents the pathogen from spreading. Another effector triggered a similar reaction, suggesting that trees may use these proteins to detect and resist attacks.

Interestingly, when researchers tested these effectors on Nicotiana benthamiana (a relative of tobacco and tomatoes, and very different from pine trees), the plants also reacted. This indicates that these effectors can even trigger plant immunity across different species. The study also showed that while some effectors share similar amino acid sequences, others are structurally alike despite having little sequence similarity, highlighting the crucial role of protein folding and shape in their function.

Understanding these shared effectors is exciting because it could lead to stronger, disease-resistant trees. If scientists can breed pines that recognise these common effectors, forests could naturally resist multiple diseases at once, reducing the need for chemical treatments. This study highlights the ongoing “arms race” between plants and pathogens, in which both constantly evolve to outsmart one another. By better understanding these interactions at the molecular level, scientists are helping trees fight back.

Figure: Figure demonstrating defence-triggering effector proteins.

TITLE IMAGE: Pine infected with the Dothistroma needle blight fungus. Image credit to Rosie Bradshaw.