Molecular genetic mechanisms governing CO2 assimilation in CAM plants

Crassulacean acid metabolism (CAM) is an important adaptation of photosynthetic carbon fixation to transient or limited water availability that improves water use efficiency and is present in more than 7% of vascular plant species. The remarkable biochemical and physiological plasticity of CAM in the context of diverse ecological settings is governed by a combination of genotypic, ontogenetic, and environmental factors. Functional genomics approaches in C3/CAM-intermediate models such as the common ice plant, Mesembryanthemum crystallinum, offer novel insights into the signal transduction pathways, the transcriptional, posttranscriptional and posttranslational regulatory events controlling gene expression, and the molecular genetic basis of the circadian oscillator that governs carbon flux during CAM. Gene discovery efforts using expressed sequence tags (EST), cDNA microarray analysis, coupled with the screening and isolation of mutants defective in CAM and the development of efficient transformation technologies set the stage for systematic functional analysis of the complex regulatory dynamics involved in CAM induction and modulation by environmental and circadian cues. Such information will have broad significance as the ecological and agricultural importance of CAM species is expected to increase in view of global warming trends and associated expansion of semi-arid and arid regions around the world.