AS WEEDS GO, Arabidopsis thaliana is a rather charming specimen. On a spring day, you might see it sprouting from the cracks of a parking lot, unleashing a small riot of white flowers that give it the common name “mouse ear cress.” But its rotund leaves often bear unwelcome passengers: among them, a bacteria called Pseudomonas syringae. It sits there looking for a way into the plant, usually the stomata through which the leaf takes in water and carbon dioxide, or through a wound. That’s when things get interesting.

Typically, the first warning of the invasion comes from receptors that tell the plant cells to unleash their defenses. Among the most important is a hormone called salicylic acid (SA). It’s used not just by arabidopsis, but by many other plants, including major crops, to stave off infections. But imagine that this spring day is unusually hot. A few days into a passing heat wave, you’ll see that the plant’s leaves are growing yellow and withered. Its immune system seems to be failing.

For much of the past decade, Sheng-Yang He, a plant biologist at Duke University, has been studying why plant immune systems fail in the heat. It’s a molecular mystery that involves unpacking dozens of genes to figure out why plants can no longer produce important chemicals, like SA, when temperatures rise just a few degrees. That’s the kind of dysfunction that is expected to become vastly more common for all sorts of plants as the climate changes and heat waves become more intense and frequent. And now, in a paper published in Nature, He’s team describes how that immunity can be restored.