Soybeans and other legumes form symbiotic relationships with nitrogen-fixing bacteria in root nodules, thus ensuring that the plant a ready supply of the necessary nutrient. Wang et al. worked out the signaling pathways that integrate above-ground light with below-ground root nodulation. Two mobile regulators move from shoot to root in response to light, and together they form a signaling module in the root that induces the expression of nodulation factors. Thus, when the shoot sees enough light to support photosynthetic productivity, the root gets the signal to ramp up nitrogen fixation.