Extreme cooling enables survival in extreme heat

Complex, multicellular extremophiles face intense challenges in coordinating their cells, tissues, and organs to function in harsh environments. Tidestromia oblongifolia is a desert plant that thrives in Death Valley, where air temperatures exceed 49 {degrees}C. Using natural collections of T. oblongifolia seed, we identified individuals that survive in daily air temperature regimens at the eukaryotic upper thermal limit of 60 {degrees}C. Genome-wide association testing detected genetic variation for survival in extreme heat, and transcriptomics implicated pathways regulating leaf cooling. High-throughput infrared imaging revealed that survival was enabled by leaf cooling far below air temperature, identifying a physiological mechanism of thermophily in a multicellular organism. These discoveries provide insights into mechanisms of extreme heat adaptation that could be leveraged to engineer heat-resilient crops.