ON THE COVER

Crassulacean acid metabolism (CAM) is a highly water-use-efficient metabolic adaptation of photosynthetic CO₂ fixation that is under strict temporal control mediated by the endogenous circadian clock. Boxall et al. (pages 2519–2536) investigated the importance of a key circadian clock-controlled protein kinase, phosphoenolpyruvate carboxylase kinase (PPCK), for optimized primary nocturnal CO₂ fixation during CAM. The CAM-associated PPCK1 gene was silenced using an RNAi approach in the model CAM species Kalancho fedtschenkoi. Two-thirds of nocturnal CO₂ fixation was lost in the absence of PPCK1, and this led to feedback misregulation of key genes within the core circadian oscillator. The cover image shows the succulent, CAM-performing leaves of K. fedtschenkoi plants, a species that is endemic to Madagascar. The leaves in the center display characteristic adventitious leaf margin plantlets, a valuable trait for rapid clonal propagation of stable transgenic lines.