All light and no night makes the tomato a dull, sickly fruit. If commercial varieties of tomato plants are exposed to 24-hour-a-day light, as they sometimes are in a greenhouse, their leaves become mottled with yellow spots, as in the photo above, and the plants can die. Now, researchers have discovered that a gene that makes a protein called CAB-13, which plays a role in photosynthesis, also boosts tomatoes’ tolerance for round-the-clock exposure to light. This little-studied gene is prevalent in wild varieties of tomatoes but is mutated in most commercial varieties, rendering them vulnerable to continuous illumination, the team notes. When the researchers bred some domestic tomatoes with their wild kin for several generations and restored the gene’s function, the resulting varieties were tolerant of 24-hour light, they report online today in Nature Communications. Some of the new plants even thrive under it, producing 20% more tomatoes when grown under 24-hour light as opposed to cycles of 16 hours of light and 8 hours of darkness. The finding, besides offering opportunities for researchers to develop novel strains of light-tolerant, more bountiful tomatoes, may help scientists better understand the biochemical processes involved in photosynthesis.