RT Journal Article SR Electronic T1 Underwater CAM photosynthesis elucidated by Isoetes genome JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.06.09.447806 DO 10.1101/2021.06.09.447806 A1 David Wickell A1 Li-Yaung Kuo A1 Hsiao-Pei Yang A1 Amra Dhabalia Ashok A1 Iker Irisarri A1 Armin Dadras A1 Sophie de Vries A1 Jan de Vries A1 Yao-Moan Huang A1 Zheng Li A1 Michael S. Barker A1 Nolan T. Hartwick A1 Todd P. Michael A1 Fay-Wei Li YR 2021 UL http://biorxiv.org/content/early/2021/06/10/2021.06.09.447806.abstract AB To conserve water in arid environments, numerous plant lineages have independently evolved Crassulacean Acid Metabolism (CAM). Interestingly, Isoetes, an aquatic lycophyte, can also perform CAM as an adaptation to low CO2 availability underwater. However, little is known about the evolution of CAM in aquatic plants and the lack of genomic data has hindered comparison between aquatic and terrestrial CAM. Here, we investigated the underwater CAM in Isoetes taiwanensis by generating a high-quality genome assembly and RNA-seq time course. Despite broad similarities between CAM in Isoetes and terrestrial angiosperms, we identified several key differences. Notably, for carboxylation of PEP, Isoetes recruited the lesser-known “bacterial-type” PEPC, along with the “plant-type” exclusively used in other terrestrial CAM and C4 plants. Furthermore, we found that circadian control of key CAM pathway genes has diverged considerably in Isoetes relative to flowering plants. This suggests the existence of more evolutionary paths to CAM than previously recognized.Competing Interest StatementThe authors have declared no competing interest.