Meeting Abstract
Photosynthetic organisms are the foundation of ecosystems across the globe, yet the photosynthetic pathway is highly susceptible to stress via water limitation. Plants that live in desert or in other water-limited habitats can close stomata to preserve water, but frequent or prolonged stomatal closure prevents CO2 from entering the cells and will eventually starve plants of carbon. To circumvent this problem, multiple lineages of flowering plants have evolved a modified form of photosynthesis known as Crassulacean acid metabolism (CAM). CAM plants, which comprise 7% of all flowering plants and have evolved at least 35 independent times, open their stomata at night to acquire CO2 when temperatures are lower and less water is lost to the atmosphere. CAM plants store the CO2 acquired at night as malic acid in their cells, then during the day close stomata and decarboxylate the malic acid. The result is high concentrations of CO2 in the cells for efficient photosynthesis, all while minimizing water loss. CAM is remarkable, in that its evolution requires plants to modify a central metabolic pathway without significant losses in fitness. To understand the physiological and genomic landscape that may have preceded the evolution of CAM, we investigated the drought response and ability to upregulate CAM in the C3-CAM hybrid Yucca gloriosa. Using a combination of gas exchange measurements and time course RNAseq, we show variation in how genotypes respond to drought stress, how much they can rely on the CAM phenotype, and significant variation in gene expression, including in circadian clock regulatory pathways. While there is variation among genotypes, the variation is limited in its extremes, suggesting a small phenotypic and genotypic space where the fitness of the hybrid remains sufficiently high for survival.
