*Review* **Cyclic AMP: A Polyhedral Signalling Molecule in Plants**

#### **Emanuela Blanco 1,\*, Stefania Fortunato 2, Luigi Viggiano 2 and Maria Concetta de Pinto 2,\***


Received: 14 June 2020; Accepted: 7 July 2020; Published: 9 July 2020

**Abstract:** The cyclic nucleotide cAMP (3-,5--cyclic adenosine monophosphate) is nowadays recognised as an important signalling molecule in plants, involved in many molecular processes, including sensing and response to biotic and abiotic environmental stresses. The validation of a functional cAMP-dependent signalling system in higher plants has spurred a grea<sup>t</sup> scientific interest on the polyhedral role of cAMP, as it actively participates in plant adaptation to external stimuli, in addition to the regulation of physiological processes. The complex architecture of cAMP-dependent pathways is far from being fully understood, because the actors of these pathways and their downstream target proteins remain largely unidentified. Recently, a genetic strategy was effectively used to lower cAMP cytosolic levels and hence shed light on the consequences of cAMP deficiency in plant cells. This review aims to provide an integrated overview of the current state of knowledge on cAMP's role in plant growth and response to environmental stress. Current knowledge of the molecular components and the mechanisms of cAMP signalling events is summarised.

**Keywords:** abiotic stress; cAMP; cyclic nucleotides-gated channels; plant innate immunity
