Abstract

In animals, ADP -ribosyl cyclase (ADPR cyclase) is a multifunctional enzyme that catalyses nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) into two important second messengers, cyclic ADP -ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP), respectively. cADPR targets the ryanodine receptor (RyR) present in the sarco/endoplasmic reticulum (SR/ER) and acts as a potent calcium mobiliser in the cell. cADPR elevates cytosolic free Ca2+ [Ca2+]cyt in plants and plays a central role in signal transduction pathways evoked by the drought and stress hormone, abscisic acid (ABA). We found that cADPR-mediated [Ca2+]cyt forms an additional cytosolic loop of the circadian clock in Arabidopsis. CIRCADIAN CLOCK ASSOCIATED1 (CCA1) acts as a repressor of ADPR cyclase activity and in the absence of PSEUDORESPONSE REGULATOR9 (PRR9), and PRR579 the activity of CCA1 is increased, thereby reducing the activity of ADPR cyclase in Arabidopsis, consistent with the circadian regulation of [Ca2+]cyt. I will be talking about how cADPR-mediated [Ca2+]cyt is incorporated into the circadian clock and some aspects of the purification process of ADPR cyclase.