Their bioluminescent system consists of a protein called luciferase that can break down the fuel to produce light, called luciferin. This process is so efficient that it hardly produces any heat, Amirav-Drory recently told DNews' Anthony Carboni (video).
That luciferase-luciferin system enables fireflies, fungi and some bacteria to glow. Getting that to happen in plants is fairly complicated so the Glowing Plant team used a prototyping method that relies on an agrobacterium. Although this agrobacterium can inject part of its genome into a plant, unfortunately it's also a highly regulated plant pest.
If you're worried about this all going awry and creating glowing weeds everywhere, fear not. The team is only using the agrobacterium to figure out what works best in the lab - they'll use a safer method for the actual production. And Amirav-Drory told DNews that adding bioluminescence removes energy from cells so these plants will be less adaptable than normal ones in the evolutionary sense.