Circadian Regulation of Pineapple CAM Photosynthesis
The altered carbon assimilation pathway of crassulacean acid metabolism (CAM) evolved as an adaptation to arid environments, and it confers 80% greater water use efficiency than the C3 pathway. Pineapple is the most economically valuable crop possessing CAM, and its wealth of genetic and genomic resources make it an excellent model for dissecting the molecular basis of this important pathway. Decades of physiology studies in pineapple identified the underlying biochemistry of CAM, but this work yielded little insight into the regulation and circadian control of CAM. High-resolution transcriptome surveys across the pineapple leaf gradient and throughout a diurnal time course were recently collected. This work uncovered new CAM-associated genes and suggested CAM evolved through neofunctionalization of existing gene copies and not through gene duplication events. CAM pathway genes are enriched with cis-regulatory elements associated with regulation by circadian clock genes. This includes novel clock-associated cis-regulatory elements in several stomatal movement genes, which may be related to nocturnal stomatal conductance in CAM plants. Together, these resources in pineapple provide a foundation for targeted engineering of CAM into C3 crop species.
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