Dual function plant cryptic nucleotide cyclases

Cyclic nucleotides, cAMP and cGMP, are now recognized as well-established signaling molecules in plant developmental and physiological processes, as well as in responses to both biotic and abiotic stresses. Over the past two decades, extensive research efforts have resulted in the identification of cyclic nucleotide-generating enzymes, adenylate cyclase (AC) and guanylate cyclase (GC), in higher plants. Many of these GCs and ACs are hidden in small regions of moonlighting proteins, in which AC and GC cooperate with other functional domains with well-defined primary roles. The relatively low activity of cyclase domains embedded within larger proteins has led to their classification as cryptic nucleotide cyclases. This chapter focuses on plant moonlighting nucleotide cyclases, with an emphasis on the high diversity of domain organizations, including receptor kinases, ion channels, and nitric oxide sensors. Considering the presence of several moonlighting nucleotide cyclases in distinct cell compartments and the cyclase-phosphodiesterase dual architecture, this chapter discusses the production of spatially separated stimulus-specific cellular signaling.