Together we “CAM”: 12 open questions in Crassulacean acid metabolism biology

BACKGROUND: Crassulacean acid metabolism (CAM) is a remarkable example of convergent evolution and is a versatile photosynthetic adaptation across the tree of life. It often receives less research attention than C3 or C4 photosynthesis, but as the consequences of climate change become more drastic, research into bioengineering CAM has become increasingly timely for its adaptive advantage during drought. Regardless of a biotechnological application, several aspects of CAM biology are still poorly understood. SCOPE: Here, we highlight 12 questions that have the potential to advance the field of CAM biology, covering a wide range of topics, from mechanistic, physiological, evolutionary to applied themes, including stomatal kinetics, vacuolar malate transport, mitochondrial respiration, the circadian clock, phenotypic definitions, sensing stress to induce CAM, ecophysiological significance of CAM, phytohormone signaling, multi-level molecular regulation, genetic engineering, climate change, and evolution of CAM. Overall, we also highlight the ultimate need for exploring the numerous CAM phenotypes instead of only model species. CONCLUSIONS: This perspective article provides a broad yet detailed overview of CAM biology and aims to inspire more work in the field. We aimed to highlight key knowledge gaps and future research opportunities, thereby underscoring the timely significance and relevance of CAM.