Draft Genome Sequence of the Common Ice Plant (Mesembryanthemum crystallinum L.) a Facultative Crassulacean Acid Metabolism (CAM) and Halophytic Plant Model

Crassulacean acid metabolism (CAM) is an elaboration of C₃ photosynthetic that limits atmospheric CO₂ fixation to all or part of the nighttime thereby reducing transpiration during the day and improving water-use efficiency. The common or crystalline ice plant (Mesembryanthemum crystallinum L.) is a facultative CAM and halophytic model species that can switch from C₃ photosynthesis to CAM following high salinity or water-deficit stress treatments. The estimated genome size of ice plant is 390 Mb in 9 chromosomes (2N=18). To reveal the molecular basis of halophytism and CAM, the ice plant genome is being sequenced and analyzed through hybrid assembly approaches. Results from three different sequencing platforms, Illumina Mate Pair (MP), Illumina Paired End (PE) and PacBio (PB) long reads, that are being used to sequence the genome will be discussed. Two strategies will be applied for hybrid assembly of the genome. Strategy 1 will build contigs from PB reads after error-correction by PE data followed by scaffolding using MP reads. Strategy 2 will rely on the assembly of contigs build from PE reads combined with scaffold assembly using MP reads, followed by gap filling with PB reads. The completed ice plant genome sequence will facilitate our understanding of the genomic basis of salt tolerance and the water-use efficiency that permits CAM species to inhabit semi-arid and arid environments.